/*
 * Copyright (c) 1999, 2020, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

//todo: one might eliminate uninits.andSets when monotonic

package com.sun.tools.javac.comp;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Set;
import java.util.stream.Collectors;

import com.sun.source.tree.LambdaExpressionTree.BodyKind;
import com.sun.tools.javac.code.*;
import com.sun.tools.javac.code.Scope.WriteableScope;
import com.sun.tools.javac.code.Source.Feature;
import com.sun.tools.javac.resources.CompilerProperties.Errors;
import com.sun.tools.javac.resources.CompilerProperties.Warnings;
import com.sun.tools.javac.tree.*;
import com.sun.tools.javac.util.*;
import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
import com.sun.tools.javac.util.JCDiagnostic.Error;
import com.sun.tools.javac.util.JCDiagnostic.Warning;

import com.sun.tools.javac.code.Symbol.*;
import com.sun.tools.javac.tree.JCTree.*;

import static com.sun.tools.javac.code.Flags.*;
import static com.sun.tools.javac.code.Flags.BLOCK;
import static com.sun.tools.javac.code.Kinds.Kind.*;
import static com.sun.tools.javac.code.TypeTag.BOOLEAN;
import static com.sun.tools.javac.code.TypeTag.VOID;
import static com.sun.tools.javac.tree.JCTree.Tag.*;

This pass implements dataflow analysis for Java programs though
 different AST visitor steps. Liveness analysis (see AliveAnalyzer) checks that
 every statement is reachable. Exception analysis (see FlowAnalyzer) ensures that
 every checked exception that is thrown is declared or caught.  Definite assignment analysis
 (see AssignAnalyzer) ensures that each variable is assigned when used.  Definite
 unassignment analysis (see AssignAnalyzer) in ensures that no final variable
 is assigned more than once. Finally, local variable capture analysis (see CaptureAnalyzer)
 determines that local variables accessed within the scope of an inner class/lambda
 are either final or effectively-final.
 
The JLS has a number of problems in the
 specification of these flow analysis problems. This implementation
 attempts to address those issues.
 
First, there is no accommodation for a finally clause that cannot
 complete normally. For liveness analysis, an intervening finally
 clause can cause a break, continue, or return not to reach its
 target.  For exception analysis, an intervening finally clause can
 cause any exception to be "caught".  For DA/DU analysis, the finally
 clause can prevent a transfer of control from propagating DA/DU
 state to the target.  In addition, code in the finally clause can
 affect the DA/DU status of variables.
 
For try statements, we introduce the idea of a variable being
 definitely unassigned "everywhere" in a block.  A variable V is
 "unassigned everywhere" in a block iff it is unassigned at the
 beginning of the block and there is no reachable assignment to V
 in the block.  An assignment V=e is reachable iff V is not DA
 after e.  Then we can say that V is DU at the beginning of the
 catch block iff V is DU everywhere in the try block.  Similarly, V
 is DU at the beginning of the finally block iff V is DU everywhere
 in the try block and in every catch block.  Specifically, the
 following bullet is added to 16.2.2
 
     V is unassigned everywhere in a block if it is
     unassigned before the block and there is no reachable
     assignment to V within the block.
 
 
In 16.2.15, the third bullet (and all of its sub-bullets) for all
 try blocks is changed to
 
     V is definitely unassigned before a catch block iff V is
     definitely unassigned everywhere in the try block.
 
 
The last bullet (and all of its sub-bullets) for try blocks that
 have a finally block is changed to
 
     V is definitely unassigned before the finally block iff
     V is definitely unassigned everywhere in the try block
     and everywhere in each catch block of the try statement.
 
 
In addition,
 
     V is definitely assigned at the end of a constructor iff
     V is definitely assigned after the block that is the body
     of the constructor and V is definitely assigned at every
     return that can return from the constructor.
 
 
In addition, each continue statement with the loop as its target
 is treated as a jump to the end of the loop body, and "intervening"
 finally clauses are treated as follows: V is DA "due to the
 continue" iff V is DA before the continue statement or V is DA at
 the end of any intervening finally block.  V is DU "due to the
 continue" iff any intervening finally cannot complete normally or V
 is DU at the end of every intervening finally block.  This "due to
 the continue" concept is then used in the spec for the loops.
 
Similarly, break statements must consider intervening finally
 blocks.  For liveness analysis, a break statement for which any
 intervening finally cannot complete normally is not considered to
 cause the target statement to be able to complete normally. Then
 we say V is DA "due to the break" iff V is DA before the break or
 V is DA at the end of any intervening finally block.  V is DU "due
 to the break" iff any intervening finally cannot complete normally
 or V is DU at the break and at the end of every intervening
 finally block.  (I suspect this latter condition can be
 simplified.)  This "due to the break" is then used in the spec for
 all statements that can be "broken".
 
The return statement is treated similarly.  V is DA "due to a
 return statement" iff V is DA before the return statement or V is
 DA at the end of any intervening finally block.  Note that we
 don't have to worry about the return expression because this
 concept is only used for construcrors.
 
There is no spec in the JLS for when a variable is definitely
 assigned at the end of a constructor, which is needed for final
 fields (8.3.1.2).  We implement the rule that V is DA at the end
 of the constructor iff it is DA and the end of the body of the
 constructor and V is DA "due to" every return of the constructor.
 
Intervening finally blocks similarly affect exception analysis.  An
 intervening finally that cannot complete normally allows us to ignore
 an otherwise uncaught exception.
 
To implement the semantics of intervening finally clauses, all nonlocal transfers (break, continue, return, throw, method call that can throw a checked exception, and a constructor invocation that can thrown a checked exception) are recorded in a queue, and removed from the queue when we complete processing the target of the nonlocal transfer. This allows us to modify the queue in accordance with the above rules when we encounter a finally clause. The only exception to this [no pun intended] is that checked exceptions that are known to be caught or declared to be caught in the enclosing method are not recorded in the queue, but instead are recorded in a global variable "Set<Type> thrown" that records the type of all exceptions that can be thrown. 
Other minor issues the treatment of members of other classes
 (always considered DA except that within an anonymous class
 constructor, where DA status from the enclosing scope is
 preserved), treatment of the case expression (V is DA before the
 case expression iff V is DA after the switch expression),
 treatment of variables declared in a switch block (the implied
 DA/DU status after the switch expression is DU and not DA for
 variables defined in a switch block), the treatment of boolean ?:
 expressions (The JLS rules only handle b and c non-boolean; the
 new rule is that if b and c are boolean valued, then V is
 (un)assigned after a?b:c when true/false iff V is (un)assigned
 after b when true/false and V is (un)assigned after c when
 true/false).
 
There is the remaining question of what syntactic forms constitute a
 reference to a variable.  It is conventional to allow this.x on the
 left-hand-side to initialize a final instance field named x, yet
 this.x isn't considered a "use" when appearing on a right-hand-side
 in most implementations.  Should parentheses affect what is
 considered a variable reference?  The simplest rule would be to
 allow unqualified forms only, parentheses optional, and phase out
 support for assigning to a final field via this.x.
 
This is NOT part of any supported API.
 If you write code that depends on this, you do so at your own risk.
 This code and its internal interfaces are subject to change or
 deletion without notice.
/** This pass implements dataflow analysis for Java programs though
 *  different AST visitor steps. Liveness analysis (see AliveAnalyzer) checks that
 *  every statement is reachable. Exception analysis (see FlowAnalyzer) ensures that
 *  every checked exception that is thrown is declared or caught.  Definite assignment analysis
 *  (see AssignAnalyzer) ensures that each variable is assigned when used.  Definite
 *  unassignment analysis (see AssignAnalyzer) in ensures that no final variable
 *  is assigned more than once. Finally, local variable capture analysis (see CaptureAnalyzer)
 *  determines that local variables accessed within the scope of an inner class/lambda
 *  are either final or effectively-final.
 *
 *  <p>The JLS has a number of problems in the
 *  specification of these flow analysis problems. This implementation
 *  attempts to address those issues.
 *
 *  <p>First, there is no accommodation for a finally clause that cannot
 *  complete normally. For liveness analysis, an intervening finally
 *  clause can cause a break, continue, or return not to reach its
 *  target.  For exception analysis, an intervening finally clause can
 *  cause any exception to be "caught".  For DA/DU analysis, the finally
 *  clause can prevent a transfer of control from propagating DA/DU
 *  state to the target.  In addition, code in the finally clause can
 *  affect the DA/DU status of variables.
 *
 *  <p>For try statements, we introduce the idea of a variable being
 *  definitely unassigned "everywhere" in a block.  A variable V is
 *  "unassigned everywhere" in a block iff it is unassigned at the
 *  beginning of the block and there is no reachable assignment to V
 *  in the block.  An assignment V=e is reachable iff V is not DA
 *  after e.  Then we can say that V is DU at the beginning of the
 *  catch block iff V is DU everywhere in the try block.  Similarly, V
 *  is DU at the beginning of the finally block iff V is DU everywhere
 *  in the try block and in every catch block.  Specifically, the
 *  following bullet is added to 16.2.2
 *  <pre>
 *      V is <em>unassigned everywhere</em> in a block if it is
 *      unassigned before the block and there is no reachable
 *      assignment to V within the block.
 *  </pre>
 *  <p>In 16.2.15, the third bullet (and all of its sub-bullets) for all
 *  try blocks is changed to
 *  <pre>
 *      V is definitely unassigned before a catch block iff V is
 *      definitely unassigned everywhere in the try block.
 *  </pre>
 *  <p>The last bullet (and all of its sub-bullets) for try blocks that
 *  have a finally block is changed to
 *  <pre>
 *      V is definitely unassigned before the finally block iff
 *      V is definitely unassigned everywhere in the try block
 *      and everywhere in each catch block of the try statement.
 *  </pre>
 *  <p>In addition,
 *  <pre>
 *      V is definitely assigned at the end of a constructor iff
 *      V is definitely assigned after the block that is the body
 *      of the constructor and V is definitely assigned at every
 *      return that can return from the constructor.
 *  </pre>
 *  <p>In addition, each continue statement with the loop as its target
 *  is treated as a jump to the end of the loop body, and "intervening"
 *  finally clauses are treated as follows: V is DA "due to the
 *  continue" iff V is DA before the continue statement or V is DA at
 *  the end of any intervening finally block.  V is DU "due to the
 *  continue" iff any intervening finally cannot complete normally or V
 *  is DU at the end of every intervening finally block.  This "due to
 *  the continue" concept is then used in the spec for the loops.
 *
 *  <p>Similarly, break statements must consider intervening finally
 *  blocks.  For liveness analysis, a break statement for which any
 *  intervening finally cannot complete normally is not considered to
 *  cause the target statement to be able to complete normally. Then
 *  we say V is DA "due to the break" iff V is DA before the break or
 *  V is DA at the end of any intervening finally block.  V is DU "due
 *  to the break" iff any intervening finally cannot complete normally
 *  or V is DU at the break and at the end of every intervening
 *  finally block.  (I suspect this latter condition can be
 *  simplified.)  This "due to the break" is then used in the spec for
 *  all statements that can be "broken".
 *
 *  <p>The return statement is treated similarly.  V is DA "due to a
 *  return statement" iff V is DA before the return statement or V is
 *  DA at the end of any intervening finally block.  Note that we
 *  don't have to worry about the return expression because this
 *  concept is only used for construcrors.
 *
 *  <p>There is no spec in the JLS for when a variable is definitely
 *  assigned at the end of a constructor, which is needed for final
 *  fields (8.3.1.2).  We implement the rule that V is DA at the end
 *  of the constructor iff it is DA and the end of the body of the
 *  constructor and V is DA "due to" every return of the constructor.
 *
 *  <p>Intervening finally blocks similarly affect exception analysis.  An
 *  intervening finally that cannot complete normally allows us to ignore
 *  an otherwise uncaught exception.
 *
 *  <p>To implement the semantics of intervening finally clauses, all
 *  nonlocal transfers (break, continue, return, throw, method call that
 *  can throw a checked exception, and a constructor invocation that can
 *  thrown a checked exception) are recorded in a queue, and removed
 *  from the queue when we complete processing the target of the
 *  nonlocal transfer.  This allows us to modify the queue in accordance
 *  with the above rules when we encounter a finally clause.  The only
 *  exception to this [no pun intended] is that checked exceptions that
 *  are known to be caught or declared to be caught in the enclosing
 *  method are not recorded in the queue, but instead are recorded in a
 *  global variable "{@code Set<Type> thrown}" that records the type of all
 *  exceptions that can be thrown.
 *
 *  <p>Other minor issues the treatment of members of other classes
 *  (always considered DA except that within an anonymous class
 *  constructor, where DA status from the enclosing scope is
 *  preserved), treatment of the case expression (V is DA before the
 *  case expression iff V is DA after the switch expression),
 *  treatment of variables declared in a switch block (the implied
 *  DA/DU status after the switch expression is DU and not DA for
 *  variables defined in a switch block), the treatment of boolean ?:
 *  expressions (The JLS rules only handle b and c non-boolean; the
 *  new rule is that if b and c are boolean valued, then V is
 *  (un)assigned after a?b:c when true/false iff V is (un)assigned
 *  after b when true/false and V is (un)assigned after c when
 *  true/false).
 *
 *  <p>There is the remaining question of what syntactic forms constitute a
 *  reference to a variable.  It is conventional to allow this.x on the
 *  left-hand-side to initialize a final instance field named x, yet
 *  this.x isn't considered a "use" when appearing on a right-hand-side
 *  in most implementations.  Should parentheses affect what is
 *  considered a variable reference?  The simplest rule would be to
 *  allow unqualified forms only, parentheses optional, and phase out
 *  support for assigning to a final field via this.x.
 *
 *  <p><b>This is NOT part of any supported API.
 *  If you write code that depends on this, you do so at your own risk.
 *  This code and its internal interfaces are subject to change or
 *  deletion without notice.</b>
 */
public class Flow {
    protected static final Context.Key<Flow> flowKey = new Context.Key<>();

    private final Names names;
    private final Log log;
    private final Symtab syms;
    private final Types types;
    private final Check chk;
    private       TreeMaker make;
    private final Resolve rs;
    private final JCDiagnostic.Factory diags;
    private Env<AttrContext> attrEnv;
    private       Lint lint;
    private final boolean allowEffectivelyFinalInInnerClasses;

    public static Flow instance(Context context) {
        Flow instance = context.get(flowKey);
        if (instance == null)
            instance = new Flow(context);
        return instance;
    }

    public void analyzeTree(Env<AttrContext> env, TreeMaker make) {
        new AliveAnalyzer().analyzeTree(env, make);
        new AssignAnalyzer().analyzeTree(env, make);
        new FlowAnalyzer().analyzeTree(env, make);
        new CaptureAnalyzer().analyzeTree(env, make);
    }

    public void analyzeLambda(Env<AttrContext> env, JCLambda that, TreeMaker make, boolean speculative) {
        Log.DiagnosticHandler diagHandler = null;
        //we need to disable diagnostics temporarily; the problem is that if
        //a lambda expression contains e.g. an unreachable statement, an error
        //message will be reported and will cause compilation to skip the flow analyis
        //step - if we suppress diagnostics, we won't stop at Attr for flow-analysis
        //related errors, which will allow for more errors to be detected
        if (!speculative) {
            diagHandler = new Log.DiscardDiagnosticHandler(log);
        }
        try {
            new LambdaAliveAnalyzer().analyzeTree(env, that, make);
        } finally {
            if (!speculative) {
                log.popDiagnosticHandler(diagHandler);
            }
        }
    }

    public List<Type> analyzeLambdaThrownTypes(final Env<AttrContext> env,
            JCLambda that, TreeMaker make) {
        //we need to disable diagnostics temporarily; the problem is that if
        //a lambda expression contains e.g. an unreachable statement, an error
        //message will be reported and will cause compilation to skip the flow analyis
        //step - if we suppress diagnostics, we won't stop at Attr for flow-analysis
        //related errors, which will allow for more errors to be detected
        Log.DiagnosticHandler diagHandler = new Log.DiscardDiagnosticHandler(log);
        try {
            new LambdaAssignAnalyzer(env).analyzeTree(env, that, make);
            LambdaFlowAnalyzer flowAnalyzer = new LambdaFlowAnalyzer();
            flowAnalyzer.analyzeTree(env, that, make);
            return flowAnalyzer.inferredThrownTypes;
        } finally {
            log.popDiagnosticHandler(diagHandler);
        }
    }

    public boolean aliveAfter(Env<AttrContext> env, JCTree that, TreeMaker make) {
        //we need to disable diagnostics temporarily; the problem is that if
        //"that" contains e.g. an unreachable statement, an error
        //message will be reported and will cause compilation to skip the flow analyis
        //step - if we suppress diagnostics, we won't stop at Attr for flow-analysis
        //related errors, which will allow for more errors to be detected
        Log.DiagnosticHandler diagHandler = new Log.DiscardDiagnosticHandler(log);
        try {
            SnippetAliveAnalyzer analyzer = new SnippetAliveAnalyzer();

            analyzer.analyzeTree(env, that, make);
            return analyzer.isAlive();
        } finally {
            log.popDiagnosticHandler(diagHandler);
        }
    }

    public boolean breaksOutOf(Env<AttrContext> env, JCTree loop, JCTree body, TreeMaker make) {
        //we need to disable diagnostics temporarily; the problem is that if
        //"that" contains e.g. an unreachable statement, an error
        //message will be reported and will cause compilation to skip the flow analyis
        //step - if we suppress diagnostics, we won't stop at Attr for flow-analysis
        //related errors, which will allow for more errors to be detected
        Log.DiagnosticHandler diagHandler = new Log.DiscardDiagnosticHandler(log);
        try {
            SnippetBreakAnalyzer analyzer = new SnippetBreakAnalyzer();

            analyzer.analyzeTree(env, body, make);
            return analyzer.breaksOut();
        } finally {
            log.popDiagnosticHandler(diagHandler);
        }
    }

    
Definite assignment scan mode
/**
     * Definite assignment scan mode
     */
    enum FlowKind {
        
This is the normal DA/DU analysis mode
/**
         * This is the normal DA/DU analysis mode
         */
        NORMAL("var.might.already.be.assigned", false),
        
This is the speculative DA/DU analysis mode used to speculatively
derive assertions within loop bodies
/**
         * This is the speculative DA/DU analysis mode used to speculatively
         * derive assertions within loop bodies
         */
        SPECULATIVE_LOOP("var.might.be.assigned.in.loop", true);

        final String errKey;
        final boolean isFinal;

        FlowKind(String errKey, boolean isFinal) {
            this.errKey = errKey;
            this.isFinal = isFinal;
        }

        boolean isFinal() {
            return isFinal;
        }
    }

    protected Flow(Context context) {
        context.put(flowKey, this);
        names = Names.instance(context);
        log = Log.instance(context);
        syms = Symtab.instance(context);
        types = Types.instance(context);
        chk = Check.instance(context);
        lint = Lint.instance(context);
        rs = Resolve.instance(context);
        diags = JCDiagnostic.Factory.instance(context);
        Source source = Source.instance(context);
        allowEffectivelyFinalInInnerClasses = Feature.EFFECTIVELY_FINAL_IN_INNER_CLASSES.allowedInSource(source);
    }

    
Base visitor class for all visitors implementing dataflow analysis logic.
This class define the shared logic for handling jumps (break/continue statements).
/**
     * Base visitor class for all visitors implementing dataflow analysis logic.
     * This class define the shared logic for handling jumps (break/continue statements).
     */
    static abstract class BaseAnalyzer extends TreeScanner {

        enum JumpKind {
            BREAK(JCTree.Tag.BREAK) {
                @Override
                JCTree getTarget(JCTree tree) {
                    return ((JCBreak)tree).target;
                }
            },
            CONTINUE(JCTree.Tag.CONTINUE) {
                @Override
                JCTree getTarget(JCTree tree) {
                    return ((JCContinue)tree).target;
                }
            },
            YIELD(JCTree.Tag.YIELD) {
                @Override
                JCTree getTarget(JCTree tree) {
                    return ((JCYield)tree).target;
                }
            };

            final JCTree.Tag treeTag;

            private JumpKind(Tag treeTag) {
                this.treeTag = treeTag;
            }

            abstract JCTree getTarget(JCTree tree);
        }

        
The currently pending exits that go from current inner blocks
 to an enclosing block, in source order.
/** The currently pending exits that go from current inner blocks
         *  to an enclosing block, in source order.
         */
        ListBuffer<PendingExit> pendingExits;

        
A pending exit.  These are the statements return, break, and
 continue.  In addition, exception-throwing expressions or
 statements are put here when not known to be caught.  This
 will typically result in an error unless it is within a
 try-finally whose finally block cannot complete normally.
/** A pending exit.  These are the statements return, break, and
         *  continue.  In addition, exception-throwing expressions or
         *  statements are put here when not known to be caught.  This
         *  will typically result in an error unless it is within a
         *  try-finally whose finally block cannot complete normally.
         */
        static class PendingExit {
            JCTree tree;

            PendingExit(JCTree tree) {
                this.tree = tree;
            }

            void resolveJump() {
                //do nothing
            }
        }

        abstract void markDead();

        
Record an outward transfer of control. /** Record an outward transfer of control. */
        void recordExit(PendingExit pe) {
            pendingExits.append(pe);
            markDead();
        }

        
Resolve all jumps of this statement. /** Resolve all jumps of this statement. */
        private Liveness resolveJump(JCTree tree,
                         ListBuffer<PendingExit> oldPendingExits,
                         JumpKind jk) {
            boolean resolved = false;
            List<PendingExit> exits = pendingExits.toList();
            pendingExits = oldPendingExits;
            for (; exits.nonEmpty(); exits = exits.tail) {
                PendingExit exit = exits.head;
                if (exit.tree.hasTag(jk.treeTag) &&
                        jk.getTarget(exit.tree) == tree) {
                    exit.resolveJump();
                    resolved = true;
                } else {
                    pendingExits.append(exit);
                }
            }
            return Liveness.from(resolved);
        }

        
Resolve all continues of this statement. /** Resolve all continues of this statement. */
        Liveness resolveContinues(JCTree tree) {
            return resolveJump(tree, new ListBuffer<PendingExit>(), JumpKind.CONTINUE);
        }

        
Resolve all breaks of this statement. /** Resolve all breaks of this statement. */
        Liveness resolveBreaks(JCTree tree, ListBuffer<PendingExit> oldPendingExits) {
            return resolveJump(tree, oldPendingExits, JumpKind.BREAK);
        }

        
Resolve all yields of this statement. /** Resolve all yields of this statement. */
        Liveness resolveYields(JCTree tree, ListBuffer<PendingExit> oldPendingExits) {
            return resolveJump(tree, oldPendingExits, JumpKind.YIELD);
        }

        @Override
        public void scan(JCTree tree) {
            if (tree != null && (
                    tree.type == null ||
                    tree.type != Type.stuckType)) {
                super.scan(tree);
            }
        }

        public void visitPackageDef(JCPackageDecl tree) {
            // Do nothing for PackageDecl
        }

        protected void scanSyntheticBreak(TreeMaker make, JCTree swtch) {
            if (swtch.hasTag(SWITCH_EXPRESSION)) {
                JCYield brk = make.at(Position.NOPOS).Yield(null);
                brk.target = swtch;
                scan(brk);
            } else {
                JCBreak brk = make.at(Position.NOPOS).Break(null);
                brk.target = swtch;
                scan(brk);
            }
        }
    }

    
This pass implements the first step of the dataflow analysis, namely
the liveness analysis check. This checks that every statement is reachable.
The output of this analysis pass are used by other analyzers. This analyzer
sets the 'finallyCanCompleteNormally' field in the JCTry class.
/**
     * This pass implements the first step of the dataflow analysis, namely
     * the liveness analysis check. This checks that every statement is reachable.
     * The output of this analysis pass are used by other analyzers. This analyzer
     * sets the 'finallyCanCompleteNormally' field in the JCTry class.
     */
    class AliveAnalyzer extends BaseAnalyzer {

        
A flag that indicates whether the last statement could
 complete normally.
/** A flag that indicates whether the last statement could
         *  complete normally.
         */
        private Liveness alive;

        @Override
        void markDead() {
            alive = Liveness.DEAD;
        }

    /*************************************************************************
     * Visitor methods for statements and definitions
     *************************************************************************/

        
Analyze a definition.
/** Analyze a definition.
         */
        void scanDef(JCTree tree) {
            scanStat(tree);
            if (tree != null && tree.hasTag(JCTree.Tag.BLOCK) && alive == Liveness.DEAD) {
                log.error(tree.pos(),
                          Errors.InitializerMustBeAbleToCompleteNormally);
            }
        }

        
Analyze a statement. Check that statement is reachable.
/** Analyze a statement. Check that statement is reachable.
         */
        void scanStat(JCTree tree) {
            if (alive == Liveness.DEAD && tree != null) {
                log.error(tree.pos(), Errors.UnreachableStmt);
                if (!tree.hasTag(SKIP)) alive = Liveness.RECOVERY;
            }
            scan(tree);
        }

        
Analyze list of statements.
/** Analyze list of statements.
         */
        void scanStats(List<? extends JCStatement> trees) {
            if (trees != null)
                for (List<? extends JCStatement> l = trees; l.nonEmpty(); l = l.tail)
                    scanStat(l.head);
        }

        /* ------------ Visitor methods for various sorts of trees -------------*/

        public void visitClassDef(JCClassDecl tree) {
            if (tree.sym == null) return;
            Liveness alivePrev = alive;
            ListBuffer<PendingExit> pendingExitsPrev = pendingExits;
            Lint lintPrev = lint;

            pendingExits = new ListBuffer<>();
            lint = lint.augment(tree.sym);

            try {
                // process all the static initializers
                for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {
                    if (!l.head.hasTag(METHODDEF) &&
                        (TreeInfo.flags(l.head) & STATIC) != 0) {
                        scanDef(l.head);
                    }
                }

                // process all the instance initializers
                for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {
                    if (!l.head.hasTag(METHODDEF) &&
                        (TreeInfo.flags(l.head) & STATIC) == 0) {
                        scanDef(l.head);
                    }
                }

                // process all the methods
                for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {
                    if (l.head.hasTag(METHODDEF)) {
                        scan(l.head);
                    }
                }
            } finally {
                pendingExits = pendingExitsPrev;
                alive = alivePrev;
                lint = lintPrev;
            }
        }

        public void visitMethodDef(JCMethodDecl tree) {
            if (tree.body == null) return;
            Lint lintPrev = lint;

            lint = lint.augment(tree.sym);

            Assert.check(pendingExits.isEmpty());

            try {
                alive = Liveness.ALIVE;
                scanStat(tree.body);
                tree.completesNormally = alive != Liveness.DEAD;

                if (alive == Liveness.ALIVE && !tree.sym.type.getReturnType().hasTag(VOID))
                    log.error(TreeInfo.diagEndPos(tree.body), Errors.MissingRetStmt);

                List<PendingExit> exits = pendingExits.toList();
                pendingExits = new ListBuffer<>();
                while (exits.nonEmpty()) {
                    PendingExit exit = exits.head;
                    exits = exits.tail;
                    Assert.check(exit.tree.hasTag(RETURN) ||
                                    log.hasErrorOn(exit.tree.pos()));
                }
            } finally {
                lint = lintPrev;
            }
        }

        public void visitVarDef(JCVariableDecl tree) {
            if (tree.init != null) {
                Lint lintPrev = lint;
                lint = lint.augment(tree.sym);
                try{
                    scan(tree.init);
                } finally {
                    lint = lintPrev;
                }
            }
        }

        public void visitBlock(JCBlock tree) {
            scanStats(tree.stats);
        }

        public void visitDoLoop(JCDoWhileLoop tree) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            pendingExits = new ListBuffer<>();
            scanStat(tree.body);
            alive = alive.or(resolveContinues(tree));
            scan(tree.cond);
            alive = alive.and(!tree.cond.type.isTrue());
            alive = alive.or(resolveBreaks(tree, prevPendingExits));
        }

        public void visitWhileLoop(JCWhileLoop tree) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            pendingExits = new ListBuffer<>();
            scan(tree.cond);
            alive = Liveness.from(!tree.cond.type.isFalse());
            scanStat(tree.body);
            alive = alive.or(resolveContinues(tree));
            alive = resolveBreaks(tree, prevPendingExits).or(
                !tree.cond.type.isTrue());
        }

        public void visitForLoop(JCForLoop tree) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            scanStats(tree.init);
            pendingExits = new ListBuffer<>();
            if (tree.cond != null) {
                scan(tree.cond);
                alive = Liveness.from(!tree.cond.type.isFalse());
            } else {
                alive = Liveness.ALIVE;
            }
            scanStat(tree.body);
            alive = alive.or(resolveContinues(tree));
            scan(tree.step);
            alive = resolveBreaks(tree, prevPendingExits).or(
                tree.cond != null && !tree.cond.type.isTrue());
        }

        public void visitForeachLoop(JCEnhancedForLoop tree) {
            visitVarDef(tree.var);
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            scan(tree.expr);
            pendingExits = new ListBuffer<>();
            scanStat(tree.body);
            alive = alive.or(resolveContinues(tree));
            resolveBreaks(tree, prevPendingExits);
            alive = Liveness.ALIVE;
        }

        public void visitLabelled(JCLabeledStatement tree) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            pendingExits = new ListBuffer<>();
            scanStat(tree.body);
            alive = alive.or(resolveBreaks(tree, prevPendingExits));
        }

        public void visitSwitch(JCSwitch tree) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            pendingExits = new ListBuffer<>();
            scan(tree.selector);
            boolean hasDefault = false;
            for (List<JCCase> l = tree.cases; l.nonEmpty(); l = l.tail) {
                alive = Liveness.ALIVE;
                JCCase c = l.head;
                if (c.pats.isEmpty())
                    hasDefault = true;
                else {
                    for (JCExpression pat : c.pats) {
                        scan(pat);
                    }
                }
                scanStats(c.stats);
                c.completesNormally = alive != Liveness.DEAD;
                if (alive != Liveness.DEAD && c.caseKind == JCCase.RULE) {
                    scanSyntheticBreak(make, tree);
                    alive = Liveness.DEAD;
                }
                // Warn about fall-through if lint switch fallthrough enabled.
                if (alive == Liveness.ALIVE &&
                    lint.isEnabled(Lint.LintCategory.FALLTHROUGH) &&
                    c.stats.nonEmpty() && l.tail.nonEmpty())
                    log.warning(Lint.LintCategory.FALLTHROUGH,
                                l.tail.head.pos(),
                                Warnings.PossibleFallThroughIntoCase);
            }
            if (!hasDefault) {
                alive = Liveness.ALIVE;
            }
            alive = alive.or(resolveBreaks(tree, prevPendingExits));
        }

        @Override
        public void visitSwitchExpression(JCSwitchExpression tree) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            pendingExits = new ListBuffer<>();
            scan(tree.selector);
            Set<Object> constants = null;
            if ((tree.selector.type.tsym.flags() & ENUM) != 0) {
                constants = new HashSet<>();
                for (Symbol s : tree.selector.type.tsym.members().getSymbols(s -> (s.flags() & ENUM) != 0)) {
                    constants.add(s.name);
                }
            }
            boolean hasDefault = false;
            Liveness prevAlive = alive;
            for (List<JCCase> l = tree.cases; l.nonEmpty(); l = l.tail) {
                alive = Liveness.ALIVE;
                JCCase c = l.head;
                if (c.pats.isEmpty())
                    hasDefault = true;
                else {
                    for (JCExpression pat : c.pats) {
                        scan(pat);
                        if (constants != null) {
                            if (pat.hasTag(IDENT))
                                constants.remove(((JCIdent) pat).name);
                            if (pat.type != null)
                                constants.remove(pat.type.constValue());
                        }
                    }
                }
                scanStats(c.stats);
                if (alive == Liveness.ALIVE) {
                    if (c.caseKind == JCCase.RULE) {
                        log.error(TreeInfo.diagEndPos(c.body),
                                  Errors.RuleCompletesNormally);
                    } else if (l.tail.isEmpty()) {
                        log.error(TreeInfo.diagEndPos(tree),
                                  Errors.SwitchExpressionCompletesNormally);
                    }
                }
                c.completesNormally = alive != Liveness.DEAD;
            }
            if ((constants == null || !constants.isEmpty()) && !hasDefault) {
                log.error(tree, Errors.NotExhaustive);
            }
            alive = prevAlive;
            alive = alive.or(resolveYields(tree, prevPendingExits));
        }

        public void visitTry(JCTry tree) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            pendingExits = new ListBuffer<>();
            for (JCTree resource : tree.resources) {
                if (resource instanceof JCVariableDecl) {
                    JCVariableDecl vdecl = (JCVariableDecl) resource;
                    visitVarDef(vdecl);
                } else if (resource instanceof JCExpression) {
                    scan((JCExpression) resource);
                } else {
                    throw new AssertionError(tree);  // parser error
                }
            }

            scanStat(tree.body);
            Liveness aliveEnd = alive;

            for (List<JCCatch> l = tree.catchers; l.nonEmpty(); l = l.tail) {
                alive = Liveness.ALIVE;
                JCVariableDecl param = l.head.param;
                scan(param);
                scanStat(l.head.body);
                aliveEnd = aliveEnd.or(alive);
            }
            if (tree.finalizer != null) {
                ListBuffer<PendingExit> exits = pendingExits;
                pendingExits = prevPendingExits;
                alive = Liveness.ALIVE;
                scanStat(tree.finalizer);
                tree.finallyCanCompleteNormally = alive != Liveness.DEAD;
                if (alive == Liveness.DEAD) {
                    if (lint.isEnabled(Lint.LintCategory.FINALLY)) {
                        log.warning(Lint.LintCategory.FINALLY,
                                TreeInfo.diagEndPos(tree.finalizer),
                                Warnings.FinallyCannotComplete);
                    }
                } else {
                    while (exits.nonEmpty()) {
                        pendingExits.append(exits.next());
                    }
                    alive = aliveEnd;
                }
            } else {
                alive = aliveEnd;
                ListBuffer<PendingExit> exits = pendingExits;
                pendingExits = prevPendingExits;
                while (exits.nonEmpty()) pendingExits.append(exits.next());
            }
        }

        @Override
        public void visitIf(JCIf tree) {
            scan(tree.cond);
            scanStat(tree.thenpart);
            if (tree.elsepart != null) {
                Liveness aliveAfterThen = alive;
                alive = Liveness.ALIVE;
                scanStat(tree.elsepart);
                alive = alive.or(aliveAfterThen);
            } else {
                alive = Liveness.ALIVE;
            }
        }

        public void visitBreak(JCBreak tree) {
            recordExit(new PendingExit(tree));
        }

        @Override
        public void visitYield(JCYield tree) {
            scan(tree.value);
            recordExit(new PendingExit(tree));
        }

        public void visitContinue(JCContinue tree) {
            recordExit(new PendingExit(tree));
        }

        public void visitReturn(JCReturn tree) {
            scan(tree.expr);
            recordExit(new PendingExit(tree));
        }

        public void visitThrow(JCThrow tree) {
            scan(tree.expr);
            markDead();
        }

        public void visitApply(JCMethodInvocation tree) {
            scan(tree.meth);
            scan(tree.args);
        }

        public void visitNewClass(JCNewClass tree) {
            scan(tree.encl);
            scan(tree.args);
            if (tree.def != null) {
                scan(tree.def);
            }
        }

        @Override
        public void visitLambda(JCLambda tree) {
            if (tree.type != null &&
                    tree.type.isErroneous()) {
                return;
            }

            ListBuffer<PendingExit> prevPending = pendingExits;
            Liveness prevAlive = alive;
            try {
                pendingExits = new ListBuffer<>();
                alive = Liveness.ALIVE;
                scanStat(tree.body);
                tree.canCompleteNormally = alive != Liveness.DEAD;
            }
            finally {
                pendingExits = prevPending;
                alive = prevAlive;
            }
        }

        public void visitModuleDef(JCModuleDecl tree) {
            // Do nothing for modules
        }

    /**************************************************************************
     * main method
     *************************************************************************/

        
Perform definite assignment/unassignment analysis on a tree.
/** Perform definite assignment/unassignment analysis on a tree.
         */
        public void analyzeTree(Env<AttrContext> env, TreeMaker make) {
            analyzeTree(env, env.tree, make);
        }
        public void analyzeTree(Env<AttrContext> env, JCTree tree, TreeMaker make) {
            try {
                attrEnv = env;
                Flow.this.make = make;
                pendingExits = new ListBuffer<>();
                alive = Liveness.ALIVE;
                scan(tree);
            } finally {
                pendingExits = null;
                Flow.this.make = null;
            }
        }
    }

    
This pass implements the second step of the dataflow analysis, namely
the exception analysis. This is to ensure that every checked exception that is
thrown is declared or caught. The analyzer uses some info that has been set by
the liveliness analyzer.
/**
     * This pass implements the second step of the dataflow analysis, namely
     * the exception analysis. This is to ensure that every checked exception that is
     * thrown is declared or caught. The analyzer uses some info that has been set by
     * the liveliness analyzer.
     */
    class FlowAnalyzer extends BaseAnalyzer {

        
A flag that indicates whether the last statement could
 complete normally.
/** A flag that indicates whether the last statement could
         *  complete normally.
         */
        HashMap<Symbol, List<Type>> preciseRethrowTypes;

        
The current class being defined.
/** The current class being defined.
         */
        JCClassDecl classDef;

        
The list of possibly thrown declarable exceptions.
/** The list of possibly thrown declarable exceptions.
         */
        List<Type> thrown;

        
The list of exceptions that are either caught or declared to be
 thrown.
/** The list of exceptions that are either caught or declared to be
         *  thrown.
         */
        List<Type> caught;

        class ThrownPendingExit extends BaseAnalyzer.PendingExit {

            Type thrown;

            ThrownPendingExit(JCTree tree, Type thrown) {
                super(tree);
                this.thrown = thrown;
            }
        }

        @Override
        void markDead() {
            //do nothing
        }

        /*-------------------- Exceptions ----------------------*/

        
Complain that pending exceptions are not caught.
/** Complain that pending exceptions are not caught.
         */
        void errorUncaught() {
            for (PendingExit exit = pendingExits.next();
                 exit != null;
                 exit = pendingExits.next()) {
                Assert.check(exit instanceof ThrownPendingExit);
                ThrownPendingExit thrownExit = (ThrownPendingExit) exit;
                if (classDef != null &&
                    classDef.pos == exit.tree.pos) {
                    log.error(exit.tree.pos(),
                              Errors.UnreportedExceptionDefaultConstructor(thrownExit.thrown));
                } else if (exit.tree.hasTag(VARDEF) &&
                        ((JCVariableDecl)exit.tree).sym.isResourceVariable()) {
                    log.error(exit.tree.pos(),
                              Errors.UnreportedExceptionImplicitClose(thrownExit.thrown,
                                                                      ((JCVariableDecl)exit.tree).sym.name));
                } else {
                    log.error(exit.tree.pos(),
                              Errors.UnreportedExceptionNeedToCatchOrThrow(thrownExit.thrown));
                }
            }
        }

        
Record that exception is potentially thrown and check that it
 is caught.
/** Record that exception is potentially thrown and check that it
         *  is caught.
         */
        void markThrown(JCTree tree, Type exc) {
            if (!chk.isUnchecked(tree.pos(), exc)) {
                if (!chk.isHandled(exc, caught)) {
                    pendingExits.append(new ThrownPendingExit(tree, exc));
                }
                thrown = chk.incl(exc, thrown);
            }
        }

    
Visitor methods for statements and definitions
/*************************************************************************
     * Visitor methods for statements and definitions
     *************************************************************************/

        /* ------------ Visitor methods for various sorts of trees -------------*/

        public void visitClassDef(JCClassDecl tree) {
            if (tree.sym == null) return;

            JCClassDecl classDefPrev = classDef;
            List<Type> thrownPrev = thrown;
            List<Type> caughtPrev = caught;
            ListBuffer<PendingExit> pendingExitsPrev = pendingExits;
            Lint lintPrev = lint;
            boolean anonymousClass = tree.name == names.empty;
            pendingExits = new ListBuffer<>();
            if (!anonymousClass) {
                caught = List.nil();
            }
            classDef = tree;
            thrown = List.nil();
            lint = lint.augment(tree.sym);

            try {
                // process all the static initializers
                for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {
                    if (!l.head.hasTag(METHODDEF) &&
                        (TreeInfo.flags(l.head) & STATIC) != 0) {
                        scan(l.head);
                        errorUncaught();
                    }
                }

                // add intersection of all thrown clauses of initial constructors
                // to set of caught exceptions, unless class is anonymous.
                if (!anonymousClass) {
                    boolean firstConstructor = true;
                    for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {
                        if (TreeInfo.isInitialConstructor(l.head)) {
                            List<Type> mthrown =
                                ((JCMethodDecl) l.head).sym.type.getThrownTypes();
                            if (firstConstructor) {
                                caught = mthrown;
                                firstConstructor = false;
                            } else {
                                caught = chk.intersect(mthrown, caught);
                            }
                        }
                    }
                }

                // process all the instance initializers
                for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {
                    if (!l.head.hasTag(METHODDEF) &&
                        (TreeInfo.flags(l.head) & STATIC) == 0) {
                        scan(l.head);
                        errorUncaught();
                    }
                }

                // in an anonymous class, add the set of thrown exceptions to
                // the throws clause of the synthetic constructor and propagate
                // outwards.
                // Changing the throws clause on the fly is okay here because
                // the anonymous constructor can't be invoked anywhere else,
                // and its type hasn't been cached.
                if (anonymousClass) {
                    for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {
                        if (TreeInfo.isConstructor(l.head)) {
                            JCMethodDecl mdef = (JCMethodDecl)l.head;
                            scan(mdef);
                            mdef.thrown = make.Types(thrown);
                            mdef.sym.type = types.createMethodTypeWithThrown(mdef.sym.type, thrown);
                        }
                    }
                    thrownPrev = chk.union(thrown, thrownPrev);
                }

                // process all the methods
                for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {
                    if (anonymousClass && TreeInfo.isConstructor(l.head))
                        continue; // there can never be an uncaught exception.
                    if (l.head.hasTag(METHODDEF)) {
                        scan(l.head);
                        errorUncaught();
                    }
                }

                thrown = thrownPrev;
            } finally {
                pendingExits = pendingExitsPrev;
                caught = caughtPrev;
                classDef = classDefPrev;
                lint = lintPrev;
            }
        }

        public void visitMethodDef(JCMethodDecl tree) {
            if (tree.body == null) return;

            List<Type> caughtPrev = caught;
            List<Type> mthrown = tree.sym.type.getThrownTypes();
            Lint lintPrev = lint;

            lint = lint.augment(tree.sym);

            Assert.check(pendingExits.isEmpty());

            try {
                for (List<JCVariableDecl> l = tree.params; l.nonEmpty(); l = l.tail) {
                    JCVariableDecl def = l.head;
                    scan(def);
                }
                if (TreeInfo.isInitialConstructor(tree))
                    caught = chk.union(caught, mthrown);
                else if ((tree.sym.flags() & (BLOCK | STATIC)) != BLOCK)
                    caught = mthrown;
                // else we are in an instance initializer block;
                // leave caught unchanged.

                scan(tree.body);

                List<PendingExit> exits = pendingExits.toList();
                pendingExits = new ListBuffer<>();
                while (exits.nonEmpty()) {
                    PendingExit exit = exits.head;
                    exits = exits.tail;
                    if (!(exit instanceof ThrownPendingExit)) {
                        Assert.check(exit.tree.hasTag(RETURN) ||
                                         log.hasErrorOn(exit.tree.pos()));
                    } else {
                        // uncaught throws will be reported later
                        pendingExits.append(exit);
                    }
                }
            } finally {
                caught = caughtPrev;
                lint = lintPrev;
            }
        }

        public void visitVarDef(JCVariableDecl tree) {
            if (tree.init != null) {
                Lint lintPrev = lint;
                lint = lint.augment(tree.sym);
                try{
                    scan(tree.init);
                } finally {
                    lint = lintPrev;
                }
            }
        }

        public void visitBlock(JCBlock tree) {
            scan(tree.stats);
        }

        public void visitDoLoop(JCDoWhileLoop tree) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            pendingExits = new ListBuffer<>();
            scan(tree.body);
            resolveContinues(tree);
            scan(tree.cond);
            resolveBreaks(tree, prevPendingExits);
        }

        public void visitWhileLoop(JCWhileLoop tree) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            pendingExits = new ListBuffer<>();
            scan(tree.cond);
            scan(tree.body);
            resolveContinues(tree);
            resolveBreaks(tree, prevPendingExits);
        }

        public void visitForLoop(JCForLoop tree) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            scan(tree.init);
            pendingExits = new ListBuffer<>();
            if (tree.cond != null) {
                scan(tree.cond);
            }
            scan(tree.body);
            resolveContinues(tree);
            scan(tree.step);
            resolveBreaks(tree, prevPendingExits);
        }

        public void visitForeachLoop(JCEnhancedForLoop tree) {
            visitVarDef(tree.var);
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            scan(tree.expr);
            pendingExits = new ListBuffer<>();
            scan(tree.body);
            resolveContinues(tree);
            resolveBreaks(tree, prevPendingExits);
        }

        public void visitLabelled(JCLabeledStatement tree) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            pendingExits = new ListBuffer<>();
            scan(tree.body);
            resolveBreaks(tree, prevPendingExits);
        }

        public void visitSwitch(JCSwitch tree) {
            handleSwitch(tree, tree.selector, tree.cases);
        }

        @Override
        public void visitSwitchExpression(JCSwitchExpression tree) {
            handleSwitch(tree, tree.selector, tree.cases);
        }

        private void handleSwitch(JCTree tree, JCExpression selector, List<JCCase> cases) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            pendingExits = new ListBuffer<>();
            scan(selector);
            for (List<JCCase> l = cases; l.nonEmpty(); l = l.tail) {
                JCCase c = l.head;
                scan(c.pats);
                scan(c.stats);
            }
            if (tree.hasTag(SWITCH_EXPRESSION)) {
                resolveYields(tree, prevPendingExits);
            } else {
                resolveBreaks(tree, prevPendingExits);
            }
        }

        public void visitTry(JCTry tree) {
            List<Type> caughtPrev = caught;
            List<Type> thrownPrev = thrown;
            thrown = List.nil();
            for (List<JCCatch> l = tree.catchers; l.nonEmpty(); l = l.tail) {
                List<JCExpression> subClauses = TreeInfo.isMultiCatch(l.head) ?
                        ((JCTypeUnion)l.head.param.vartype).alternatives :
                        List.of(l.head.param.vartype);
                for (JCExpression ct : subClauses) {
                    caught = chk.incl(ct.type, caught);
                }
            }

            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            pendingExits = new ListBuffer<>();
            for (JCTree resource : tree.resources) {
                if (resource instanceof JCVariableDecl) {
                    JCVariableDecl vdecl = (JCVariableDecl) resource;
                    visitVarDef(vdecl);
                } else if (resource instanceof JCExpression) {
                    scan((JCExpression) resource);
                } else {
                    throw new AssertionError(tree);  // parser error
                }
            }
            for (JCTree resource : tree.resources) {
                List<Type> closeableSupertypes = resource.type.isCompound() ?
                    types.interfaces(resource.type).prepend(types.supertype(resource.type)) :
                    List.of(resource.type);
                for (Type sup : closeableSupertypes) {
                    if (types.asSuper(sup, syms.autoCloseableType.tsym) != null) {
                        Symbol closeMethod = rs.resolveQualifiedMethod(tree,
                                attrEnv,
                                types.skipTypeVars(sup, false),
                                names.close,
                                List.nil(),
                                List.nil());
                        Type mt = types.memberType(resource.type, closeMethod);
                        if (closeMethod.kind == MTH) {
                            for (Type t : mt.getThrownTypes()) {
                                markThrown(resource, t);
                            }
                        }
                    }
                }
            }
            scan(tree.body);
            List<Type> thrownInTry = chk.union(thrown, List.of(syms.runtimeExceptionType, syms.errorType));
            thrown = thrownPrev;
            caught = caughtPrev;

            List<Type> caughtInTry = List.nil();
            for (List<JCCatch> l = tree.catchers; l.nonEmpty(); l = l.tail) {
                JCVariableDecl param = l.head.param;
                List<JCExpression> subClauses = TreeInfo.isMultiCatch(l.head) ?
                        ((JCTypeUnion)l.head.param.vartype).alternatives :
                        List.of(l.head.param.vartype);
                List<Type> ctypes = List.nil();
                List<Type> rethrownTypes = chk.diff(thrownInTry, caughtInTry);
                for (JCExpression ct : subClauses) {
                    Type exc = ct.type;
                    if (exc != syms.unknownType) {
                        ctypes = ctypes.append(exc);
                        if (types.isSameType(exc, syms.objectType))
                            continue;
                        checkCaughtType(l.head.pos(), exc, thrownInTry, caughtInTry);
                        caughtInTry = chk.incl(exc, caughtInTry);
                    }
                }
                scan(param);
                preciseRethrowTypes.put(param.sym, chk.intersect(ctypes, rethrownTypes));
                scan(l.head.body);
                preciseRethrowTypes.remove(param.sym);
            }
            if (tree.finalizer != null) {
                List<Type> savedThrown = thrown;
                thrown = List.nil();
                ListBuffer<PendingExit> exits = pendingExits;
                pendingExits = prevPendingExits;
                scan(tree.finalizer);
                if (!tree.finallyCanCompleteNormally) {
                    // discard exits and exceptions from try and finally
                    thrown = chk.union(thrown, thrownPrev);
                } else {
                    thrown = chk.union(thrown, chk.diff(thrownInTry, caughtInTry));
                    thrown = chk.union(thrown, savedThrown);
                    // FIX: this doesn't preserve source order of exits in catch
                    // versus finally!
                    while (exits.nonEmpty()) {
                        pendingExits.append(exits.next());
                    }
                }
            } else {
                thrown = chk.union(thrown, chk.diff(thrownInTry, caughtInTry));
                ListBuffer<PendingExit> exits = pendingExits;
                pendingExits = prevPendingExits;
                while (exits.nonEmpty()) pendingExits.append(exits.next());
            }
        }

        @Override
        public void visitIf(JCIf tree) {
            scan(tree.cond);
            scan(tree.thenpart);
            if (tree.elsepart != null) {
                scan(tree.elsepart);
            }
        }

        void checkCaughtType(DiagnosticPosition pos, Type exc, List<Type> thrownInTry, List<Type> caughtInTry) {
            if (chk.subset(exc, caughtInTry)) {
                log.error(pos, Errors.ExceptAlreadyCaught(exc));
            } else if (!chk.isUnchecked(pos, exc) &&
                    !isExceptionOrThrowable(exc) &&
                    !chk.intersects(exc, thrownInTry)) {
                log.error(pos, Errors.ExceptNeverThrownInTry(exc));
            } else {
                List<Type> catchableThrownTypes = chk.intersect(List.of(exc), thrownInTry);
                // 'catchableThrownTypes' cannnot possibly be empty - if 'exc' was an
                // unchecked exception, the result list would not be empty, as the augmented
                // thrown set includes { RuntimeException, Error }; if 'exc' was a checked
                // exception, that would have been covered in the branch above
                if (chk.diff(catchableThrownTypes, caughtInTry).isEmpty() &&
                        !isExceptionOrThrowable(exc)) {
                    Warning key = catchableThrownTypes.length() == 1 ?
                            Warnings.UnreachableCatch(catchableThrownTypes) :
                            Warnings.UnreachableCatch1(catchableThrownTypes);
                    log.warning(pos, key);
                }
            }
        }
        //where
            private boolean isExceptionOrThrowable(Type exc) {
                return exc.tsym == syms.throwableType.tsym ||
                    exc.tsym == syms.exceptionType.tsym;
            }

        public void visitBreak(JCBreak tree) {
            recordExit(new PendingExit(tree));
        }

        public void visitYield(JCYield tree) {
            scan(tree.value);
            recordExit(new PendingExit(tree));
        }

        public void visitContinue(JCContinue tree) {
            recordExit(new PendingExit(tree));
        }

        public void visitReturn(JCReturn tree) {
            scan(tree.expr);
            recordExit(new PendingExit(tree));
        }

        public void visitThrow(JCThrow tree) {
            scan(tree.expr);
            Symbol sym = TreeInfo.symbol(tree.expr);
            if (sym != null &&
                sym.kind == VAR &&
                (sym.flags() & (FINAL | EFFECTIVELY_FINAL)) != 0 &&
                preciseRethrowTypes.get(sym) != null) {
                for (Type t : preciseRethrowTypes.get(sym)) {
                    markThrown(tree, t);
                }
            }
            else {
                markThrown(tree, tree.expr.type);
            }
            markDead();
        }

        public void visitApply(JCMethodInvocation tree) {
            scan(tree.meth);
            scan(tree.args);
            for (List<Type> l = tree.meth.type.getThrownTypes(); l.nonEmpty(); l = l.tail)
                markThrown(tree, l.head);
        }

        public void visitNewClass(JCNewClass tree) {
            scan(tree.encl);
            scan(tree.args);
           // scan(tree.def);
            for (List<Type> l = tree.constructorType.getThrownTypes();
                 l.nonEmpty();
                 l = l.tail) {
                markThrown(tree, l.head);
            }
            List<Type> caughtPrev = caught;
            try {
                // If the new class expression defines an anonymous class,
                // analysis of the anonymous constructor may encounter thrown
                // types which are unsubstituted type variables.
                // However, since the constructor's actual thrown types have
                // already been marked as thrown, it is safe to simply include
                // each of the constructor's formal thrown types in the set of
                // 'caught/declared to be thrown' types, for the duration of
                // the class def analysis.
                if (tree.def != null)
                    for (List<Type> l = tree.constructor.type.getThrownTypes();
                         l.nonEmpty();
                         l = l.tail) {
                        caught = chk.incl(l.head, caught);
                    }
                scan(tree.def);
            }
            finally {
                caught = caughtPrev;
            }
        }

        @Override
        public void visitLambda(JCLambda tree) {
            if (tree.type != null &&
                    tree.type.isErroneous()) {
                return;
            }
            List<Type> prevCaught = caught;
            List<Type> prevThrown = thrown;
            ListBuffer<PendingExit> prevPending = pendingExits;
            try {
                pendingExits = new ListBuffer<>();
                caught = tree.getDescriptorType(types).getThrownTypes();
                thrown = List.nil();
                scan(tree.body);
                List<PendingExit> exits = pendingExits.toList();
                pendingExits = new ListBuffer<>();
                while (exits.nonEmpty()) {
                    PendingExit exit = exits.head;
                    exits = exits.tail;
                    if (!(exit instanceof ThrownPendingExit)) {
                        Assert.check(exit.tree.hasTag(RETURN) ||
                                        log.hasErrorOn(exit.tree.pos()));
                    } else {
                        // uncaught throws will be reported later
                        pendingExits.append(exit);
                    }
                }

                errorUncaught();
            } finally {
                pendingExits = prevPending;
                caught = prevCaught;
                thrown = prevThrown;
            }
        }

        public void visitModuleDef(JCModuleDecl tree) {
            // Do nothing for modules
        }

    /**************************************************************************
     * main method
     *************************************************************************/

        
Perform definite assignment/unassignment analysis on a tree.
/** Perform definite assignment/unassignment analysis on a tree.
         */
        public void analyzeTree(Env<AttrContext> env, TreeMaker make) {
            analyzeTree(env, env.tree, make);
        }
        public void analyzeTree(Env<AttrContext> env, JCTree tree, TreeMaker make) {
            try {
                attrEnv = env;
                Flow.this.make = make;
                pendingExits = new ListBuffer<>();
                preciseRethrowTypes = new HashMap<>();
                this.thrown = this.caught = null;
                this.classDef = null;
                scan(tree);
            } finally {
                pendingExits = null;
                Flow.this.make = null;
                this.thrown = this.caught = null;
                this.classDef = null;
            }
        }
    }

    
Specialized pass that performs reachability analysis on a lambda
/**
     * Specialized pass that performs reachability analysis on a lambda
     */
    class LambdaAliveAnalyzer extends AliveAnalyzer {

        boolean inLambda;

        @Override
        public void visitReturn(JCReturn tree) {
            //ignore lambda return expression (which might not even be attributed)
            recordExit(new PendingExit(tree));
        }

        @Override
        public void visitLambda(JCLambda tree) {
            if (inLambda || tree.getBodyKind() == BodyKind.EXPRESSION) {
                return;
            }
            inLambda = true;
            try {
                super.visitLambda(tree);
            } finally {
                inLambda = false;
            }
        }

        @Override
        public void visitClassDef(JCClassDecl tree) {
            //skip
        }
    }

    
Determine if alive after the given tree.
/**
     * Determine if alive after the given tree.
     */
    class SnippetAliveAnalyzer extends AliveAnalyzer {
        @Override
        public void visitClassDef(JCClassDecl tree) {
            //skip
        }
        public boolean isAlive() {
            return super.alive != Liveness.DEAD;
        }
    }

    class SnippetBreakAnalyzer extends AliveAnalyzer {
        private final Set<JCTree> seenTrees = new HashSet<>();
        private boolean breaksOut;

        public SnippetBreakAnalyzer() {
        }

        @Override
        public void visitLabelled(JCTree.JCLabeledStatement tree) {
            seenTrees.add(tree);
            super.visitLabelled(tree);
        }

        @Override
        public void visitWhileLoop(JCTree.JCWhileLoop tree) {
            seenTrees.add(tree);
            super.visitWhileLoop(tree);
        }

        @Override
        public void visitForLoop(JCTree.JCForLoop tree) {
            seenTrees.add(tree);
            super.visitForLoop(tree);
        }

        @Override
        public void visitForeachLoop(JCTree.JCEnhancedForLoop tree) {
            seenTrees.add(tree);
            super.visitForeachLoop(tree);
        }

        @Override
        public void visitDoLoop(JCTree.JCDoWhileLoop tree) {
            seenTrees.add(tree);
            super.visitDoLoop(tree);
        }

        @Override
        public void visitBreak(JCBreak tree) {
            breaksOut |= (super.alive == Liveness.ALIVE &&
                          !seenTrees.contains(tree.target));
            super.visitBreak(tree);
        }

        public boolean breaksOut() {
            return breaksOut;
        }
    }

    
Specialized pass that performs DA/DU on a lambda
/**
     * Specialized pass that performs DA/DU on a lambda
     */
    class LambdaAssignAnalyzer extends AssignAnalyzer {
        WriteableScope enclosedSymbols;
        boolean inLambda;

        LambdaAssignAnalyzer(Env<AttrContext> env) {
            enclosedSymbols = WriteableScope.create(env.enclClass.sym);
        }

        @Override
        public void visitLambda(JCLambda tree) {
            if (inLambda) {
                return;
            }
            inLambda = true;
            try {
                super.visitLambda(tree);
            } finally {
                inLambda = false;
            }
        }

        @Override
        public void visitVarDef(JCVariableDecl tree) {
            enclosedSymbols.enter(tree.sym);
            super.visitVarDef(tree);
        }
        @Override
        protected boolean trackable(VarSymbol sym) {
            return enclosedSymbols.includes(sym) &&
                   sym.owner.kind == MTH;
        }

        @Override
        public void visitClassDef(JCClassDecl tree) {
            //skip
        }
    }

    
Specialized pass that performs inference of thrown types for lambdas.
/**
     * Specialized pass that performs inference of thrown types for lambdas.
     */
    class LambdaFlowAnalyzer extends FlowAnalyzer {
        List<Type> inferredThrownTypes;
        boolean inLambda;
        @Override
        public void visitLambda(JCLambda tree) {
            if ((tree.type != null &&
                    tree.type.isErroneous()) || inLambda) {
                return;
            }
            List<Type> prevCaught = caught;
            List<Type> prevThrown = thrown;
            ListBuffer<PendingExit> prevPending = pendingExits;
            inLambda = true;
            try {
                pendingExits = new ListBuffer<>();
                caught = List.of(syms.throwableType);
                thrown = List.nil();
                scan(tree.body);
                inferredThrownTypes = thrown;
            } finally {
                pendingExits = prevPending;
                caught = prevCaught;
                thrown = prevThrown;
                inLambda = false;
            }
        }
        @Override
        public void visitClassDef(JCClassDecl tree) {
            //skip
        }
    }

    
This pass implements (i) definite assignment analysis, which ensures that
each variable is assigned when used and (ii) definite unassignment analysis,
which ensures that no final variable is assigned more than once. This visitor
depends on the results of the liveliness analyzer. This pass is also used to mark
effectively-final local variables/parameters.
/**
     * This pass implements (i) definite assignment analysis, which ensures that
     * each variable is assigned when used and (ii) definite unassignment analysis,
     * which ensures that no final variable is assigned more than once. This visitor
     * depends on the results of the liveliness analyzer. This pass is also used to mark
     * effectively-final local variables/parameters.
     */

    public class AssignAnalyzer extends BaseAnalyzer {

        
The set of definitely assigned variables.
/** The set of definitely assigned variables.
         */
        final Bits inits;

        
The set of definitely unassigned variables.
/** The set of definitely unassigned variables.
         */
        final Bits uninits;

        
The set of variables that are definitely unassigned everywhere
 in current try block. This variable is maintained lazily; it is
 updated only when something gets removed from uninits,
 typically by being assigned in reachable code.  To obtain the
 correct set of variables which are definitely unassigned
 anywhere in current try block, intersect uninitsTry and
 uninits.
/** The set of variables that are definitely unassigned everywhere
         *  in current try block. This variable is maintained lazily; it is
         *  updated only when something gets removed from uninits,
         *  typically by being assigned in reachable code.  To obtain the
         *  correct set of variables which are definitely unassigned
         *  anywhere in current try block, intersect uninitsTry and
         *  uninits.
         */
        final Bits uninitsTry;

        
When analyzing a condition, inits and uninits are null.
 Instead we have:
/** When analyzing a condition, inits and uninits are null.
         *  Instead we have:
         */
        final Bits initsWhenTrue;
        final Bits initsWhenFalse;
        final Bits uninitsWhenTrue;
        final Bits uninitsWhenFalse;

        
A mapping from addresses to variable symbols.
/** A mapping from addresses to variable symbols.
         */
        protected JCVariableDecl[] vardecls;

        
The current class being defined.
/** The current class being defined.
         */
        JCClassDecl classDef;

        
The first variable sequence number in this class definition.
/** The first variable sequence number in this class definition.
         */
        int firstadr;

        
The next available variable sequence number.
/** The next available variable sequence number.
         */
        protected int nextadr;

        
The first variable sequence number in a block that can return.
/** The first variable sequence number in a block that can return.
         */
        protected int returnadr;

        
The list of unreferenced automatic resources.
/** The list of unreferenced automatic resources.
         */
        WriteableScope unrefdResources;

        
Modified when processing a loop body the second time for DU analysis. /** Modified when processing a loop body the second time for DU analysis. */
        FlowKind flowKind = FlowKind.NORMAL;

        
The starting position of the analyzed tree /** The starting position of the analyzed tree */
        int startPos;

        public class AssignPendingExit extends BaseAnalyzer.PendingExit {

            final Bits inits;
            final Bits uninits;
            final Bits exit_inits = new Bits(true);
            final Bits exit_uninits = new Bits(true);

            public AssignPendingExit(JCTree tree, final Bits inits, final Bits uninits) {
                super(tree);
                this.inits = inits;
                this.uninits = uninits;
                this.exit_inits.assign(inits);
                this.exit_uninits.assign(uninits);
            }

            @Override
            public void resolveJump() {
                inits.andSet(exit_inits);
                uninits.andSet(exit_uninits);
            }
        }

        public AssignAnalyzer() {
            this.inits = new Bits();
            uninits = new Bits();
            uninitsTry = new Bits();
            initsWhenTrue = new Bits(true);
            initsWhenFalse = new Bits(true);
            uninitsWhenTrue = new Bits(true);
            uninitsWhenFalse = new Bits(true);
        }

        private boolean isInitialConstructor = false;

        @Override
        protected void markDead() {
            if (!isInitialConstructor) {
                inits.inclRange(returnadr, nextadr);
            } else {
                for (int address = returnadr; address < nextadr; address++) {
                    if (!(isFinalUninitializedStaticField(vardecls[address].sym))) {
                        inits.incl(address);
                    }
                }
            }
            uninits.inclRange(returnadr, nextadr);
        }

        /*-------------- Processing variables ----------------------*/

        
Do we need to track init/uninit state of this symbol?
 I.e. is symbol either a local or a blank final variable?
/** Do we need to track init/uninit state of this symbol?
         *  I.e. is symbol either a local or a blank final variable?
         */
        protected boolean trackable(VarSymbol sym) {
            return
                sym.pos >= startPos &&
                ((sym.owner.kind == MTH || sym.owner.kind == VAR ||
                isFinalUninitializedField(sym)));
        }

        boolean isFinalUninitializedField(VarSymbol sym) {
            return sym.owner.kind == TYP &&
                   ((sym.flags() & (FINAL | HASINIT | PARAMETER)) == FINAL &&
                   classDef.sym.isEnclosedBy((ClassSymbol)sym.owner));
        }

        boolean isFinalUninitializedStaticField(VarSymbol sym) {
            return isFinalUninitializedField(sym) && sym.isStatic();
        }

        
Initialize new trackable variable by setting its address field
 to the next available sequence number and entering it under that
 index into the vars array.
/** Initialize new trackable variable by setting its address field
         *  to the next available sequence number and entering it under that
         *  index into the vars array.
         */
        void newVar(JCVariableDecl varDecl) {
            VarSymbol sym = varDecl.sym;
            vardecls = ArrayUtils.ensureCapacity(vardecls, nextadr);
            if ((sym.flags() & FINAL) == 0) {
                sym.flags_field |= EFFECTIVELY_FINAL;
            }
            sym.adr = nextadr;
            vardecls[nextadr] = varDecl;
            inits.excl(nextadr);
            uninits.incl(nextadr);
            nextadr++;
        }

        
Record an initialization of a trackable variable.
/** Record an initialization of a trackable variable.
         */
        void letInit(DiagnosticPosition pos, VarSymbol sym) {
            if (sym.adr >= firstadr && trackable(sym)) {
                if ((sym.flags() & EFFECTIVELY_FINAL) != 0) {
                    if (!uninits.isMember(sym.adr)) {
                        //assignment targeting an effectively final variable
                        //makes the variable lose its status of effectively final
                        //if the variable is _not_ definitively unassigned
                        sym.flags_field &= ~EFFECTIVELY_FINAL;
                    } else {
                        uninit(sym);
                    }
                }
                else if ((sym.flags() & FINAL) != 0) {
                    if ((sym.flags() & PARAMETER) != 0) {
                        if ((sym.flags() & UNION) != 0) { //multi-catch parameter
                            log.error(pos, Errors.MulticatchParameterMayNotBeAssigned(sym));
                        }
                        else {
                            log.error(pos,
                                      Errors.FinalParameterMayNotBeAssigned(sym));
                        }
                    } else if (!uninits.isMember(sym.adr)) {
                        log.error(pos, diags.errorKey(flowKind.errKey, sym));
                    } else {
                        uninit(sym);
                    }
                }
                inits.incl(sym.adr);
            } else if ((sym.flags() & FINAL) != 0) {
                log.error(pos, Errors.VarMightAlreadyBeAssigned(sym));
            }
        }
        //where
            void uninit(VarSymbol sym) {
                if (!inits.isMember(sym.adr)) {
                    // reachable assignment
                    uninits.excl(sym.adr);
                    uninitsTry.excl(sym.adr);
                } else {
                    //log.rawWarning(pos, "unreachable assignment");//DEBUG
                    uninits.excl(sym.adr);
                }
            }

        
If tree is either a simple name or of the form this.name or
 C.this.name, and tree represents a trackable variable,
 record an initialization of the variable.
/** If tree is either a simple name or of the form this.name or
         *  C.this.name, and tree represents a trackable variable,
         *  record an initialization of the variable.
         */
        void letInit(JCTree tree) {
            tree = TreeInfo.skipParens(tree);
            if (tree.hasTag(IDENT) || tree.hasTag(SELECT)) {
                Symbol sym = TreeInfo.symbol(tree);
                if (sym.kind == VAR) {
                    letInit(tree.pos(), (VarSymbol)sym);
                }
            }
        }

        
Check that trackable variable is initialized.
/** Check that trackable variable is initialized.
         */
        void checkInit(DiagnosticPosition pos, VarSymbol sym) {
            checkInit(pos, sym, Errors.VarMightNotHaveBeenInitialized(sym));
        }

        void checkInit(DiagnosticPosition pos, VarSymbol sym, Error errkey) {
            if ((sym.adr >= firstadr || sym.owner.kind != TYP) &&
                trackable(sym) &&
                !inits.isMember(sym.adr)) {
                    log.error(pos, errkey);
                inits.incl(sym.adr);
            }
        }

        
Utility method to reset several Bits instances.
/** Utility method to reset several Bits instances.
         */
        private void resetBits(Bits... bits) {
            for (Bits b : bits) {
                b.reset();
            }
        }

        
Split (duplicate) inits/uninits into WhenTrue/WhenFalse sets
/** Split (duplicate) inits/uninits into WhenTrue/WhenFalse sets
         */
        void split(boolean setToNull) {
            initsWhenFalse.assign(inits);
            uninitsWhenFalse.assign(uninits);
            initsWhenTrue.assign(inits);
            uninitsWhenTrue.assign(uninits);
            if (setToNull) {
                resetBits(inits, uninits);
            }
        }

        
Merge (intersect) inits/uninits from WhenTrue/WhenFalse sets.
/** Merge (intersect) inits/uninits from WhenTrue/WhenFalse sets.
         */
        protected void merge() {
            inits.assign(initsWhenFalse.andSet(initsWhenTrue));
            uninits.assign(uninitsWhenFalse.andSet(uninitsWhenTrue));
        }

    /* ************************************************************************
     * Visitor methods for statements and definitions
     *************************************************************************/

        
Analyze an expression. Make sure to set (un)inits rather than
 (un)initsWhenTrue(WhenFalse) on exit.
/** Analyze an expression. Make sure to set (un)inits rather than
         *  (un)initsWhenTrue(WhenFalse) on exit.
         */
        void scanExpr(JCTree tree) {
            if (tree != null) {
                scan(tree);
                if (inits.isReset()) {
                    merge();
                }
            }
        }

        
Analyze a list of expressions.
/** Analyze a list of expressions.
         */
        void scanExprs(List<? extends JCExpression> trees) {
            if (trees != null)
                for (List<? extends JCExpression> l = trees; l.nonEmpty(); l = l.tail)
                    scanExpr(l.head);
        }

        
Analyze a condition. Make sure to set (un)initsWhenTrue(WhenFalse)
 rather than (un)inits on exit.
/** Analyze a condition. Make sure to set (un)initsWhenTrue(WhenFalse)
         *  rather than (un)inits on exit.
         */
        void scanCond(JCTree tree) {
            if (tree.type.isFalse()) {
                if (inits.isReset()) merge();
                initsWhenTrue.assign(inits);
                initsWhenTrue.inclRange(firstadr, nextadr);
                uninitsWhenTrue.assign(uninits);
                uninitsWhenTrue.inclRange(firstadr, nextadr);
                initsWhenFalse.assign(inits);
                uninitsWhenFalse.assign(uninits);
            } else if (tree.type.isTrue()) {
                if (inits.isReset()) merge();
                initsWhenFalse.assign(inits);
                initsWhenFalse.inclRange(firstadr, nextadr);
                uninitsWhenFalse.assign(uninits);
                uninitsWhenFalse.inclRange(firstadr, nextadr);
                initsWhenTrue.assign(inits);
                uninitsWhenTrue.assign(uninits);
            } else {
                scan(tree);
                if (!inits.isReset())
                    split(tree.type != syms.unknownType);
            }
            if (tree.type != syms.unknownType) {
                resetBits(inits, uninits);
            }
        }

        /* ------------ Visitor methods for various sorts of trees -------------*/

        public void visitClassDef(JCClassDecl tree) {
            if (tree.sym == null) {
                return;
            }

            Lint lintPrev = lint;
            lint = lint.augment(tree.sym);
            try {
                if (tree.sym == null) {
                    return;
                }

                JCClassDecl classDefPrev = classDef;
                int firstadrPrev = firstadr;
                int nextadrPrev = nextadr;
                ListBuffer<PendingExit> pendingExitsPrev = pendingExits;

                pendingExits = new ListBuffer<>();
                if (tree.name != names.empty) {
                    firstadr = nextadr;
                }
                classDef = tree;
                try {
                    // define all the static fields
                    for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {
                        if (l.head.hasTag(VARDEF)) {
                            JCVariableDecl def = (JCVariableDecl)l.head;
                            if ((def.mods.flags & STATIC) != 0) {
                                VarSymbol sym = def.sym;
                                if (trackable(sym)) {
                                    newVar(def);
                                }
                            }
                        }
                    }

                    // process all the static initializers
                    for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {
                        if (!l.head.hasTag(METHODDEF) &&
                            (TreeInfo.flags(l.head) & STATIC) != 0) {
                            scan(l.head);
                        }
                    }

                    // define all the instance fields
                    for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {
                        if (l.head.hasTag(VARDEF)) {
                            JCVariableDecl def = (JCVariableDecl)l.head;
                            if ((def.mods.flags & STATIC) == 0) {
                                VarSymbol sym = def.sym;
                                if (trackable(sym)) {
                                    newVar(def);
                                }
                            }
                        }
                    }

                    // process all the instance initializers
                    for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {
                        if (!l.head.hasTag(METHODDEF) &&
                            (TreeInfo.flags(l.head) & STATIC) == 0) {
                            scan(l.head);
                        }
                    }

                    // process all the methods
                    for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {
                        if (l.head.hasTag(METHODDEF)) {
                            scan(l.head);
                        }
                    }
                } finally {
                    pendingExits = pendingExitsPrev;
                    nextadr = nextadrPrev;
                    firstadr = firstadrPrev;
                    classDef = classDefPrev;
                }
            } finally {
                lint = lintPrev;
            }
        }

        public void visitMethodDef(JCMethodDecl tree) {
            if (tree.body == null) {
                return;
            }

            /*  MemberEnter can generate synthetic methods ignore them
             */
            if ((tree.sym.flags() & SYNTHETIC) != 0) {
                return;
            }

            Lint lintPrev = lint;
            lint = lint.augment(tree.sym);
            try {
                if (tree.body == null) {
                    return;
                }
                /*  Ignore synthetic methods, except for translated lambda methods.
                 */
                if ((tree.sym.flags() & (SYNTHETIC | LAMBDA_METHOD)) == SYNTHETIC) {
                    return;
                }

                final Bits initsPrev = new Bits(inits);
                final Bits uninitsPrev = new Bits(uninits);
                int nextadrPrev = nextadr;
                int firstadrPrev = firstadr;
                int returnadrPrev = returnadr;

                Assert.check(pendingExits.isEmpty());
                boolean lastInitialConstructor = isInitialConstructor;
                try {
                    isInitialConstructor = TreeInfo.isInitialConstructor(tree);

                    if (!isInitialConstructor) {
                        firstadr = nextadr;
                    }
                    for (List<JCVariableDecl> l = tree.params; l.nonEmpty(); l = l.tail) {
                        JCVariableDecl def = l.head;
                        scan(def);
                        Assert.check((def.sym.flags() & PARAMETER) != 0, "Method parameter without PARAMETER flag");
                        /*  If we are executing the code from Gen, then there can be
                         *  synthetic or mandated variables, ignore them.
                         */
                        initParam(def);
                    }
                    // else we are in an instance initializer block;
                    // leave caught unchanged.
                    scan(tree.body);

                    boolean isCompactConstructor = (tree.sym.flags() & Flags.COMPACT_RECORD_CONSTRUCTOR) != 0;
                    if (isInitialConstructor) {
                        boolean isSynthesized = (tree.sym.flags() &
                                                 GENERATEDCONSTR) != 0;
                        for (int i = firstadr; i < nextadr; i++) {
                            JCVariableDecl vardecl = vardecls[i];
                            VarSymbol var = vardecl.sym;
                            if (var.owner == classDef.sym) {
                                // choose the diagnostic position based on whether
                                // the ctor is default(synthesized) or not
                                if (isSynthesized && !isCompactConstructor) {
                                    checkInit(TreeInfo.diagnosticPositionFor(var, vardecl),
                                            var, Errors.VarNotInitializedInDefaultConstructor(var));
                                } else if (isCompactConstructor) {
                                    boolean isInstanceRecordField = var.enclClass().isRecord() &&
                                            (var.flags_field & (Flags.PRIVATE | Flags.FINAL | Flags.GENERATED_MEMBER | Flags.RECORD)) != 0 &&
                                            !var.isStatic() &&
                                            var.owner.kind == TYP;
                                    if (isInstanceRecordField) {
                                        boolean notInitialized = !inits.isMember(var.adr);
                                        if (notInitialized && uninits.isMember(var.adr) && tree.completesNormally) {
                                        /*  this way we indicate Lower that it should generate an initialization for this field
                                         *  in the compact constructor
                                         */
                                            var.flags_field |= UNINITIALIZED_FIELD;
                                        } else {
                                            checkInit(TreeInfo.diagEndPos(tree.body), var);
                                        }
                                    } else {
                                        checkInit(TreeInfo.diagnosticPositionFor(var, vardecl), var);
                                    }
                                } else {
                                    checkInit(TreeInfo.diagEndPos(tree.body), var);
                                }
                            }
                        }
                    }
                    List<PendingExit> exits = pendingExits.toList();
                    pendingExits = new ListBuffer<>();
                    while (exits.nonEmpty()) {
                        PendingExit exit = exits.head;
                        exits = exits.tail;
                        Assert.check(exit.tree.hasTag(RETURN) ||
                                         log.hasErrorOn(exit.tree.pos()),
                                     exit.tree);
                        if (isInitialConstructor) {
                            Assert.check(exit instanceof AssignPendingExit);
                            inits.assign(((AssignPendingExit) exit).exit_inits);
                            for (int i = firstadr; i < nextadr; i++) {
                                checkInit(exit.tree.pos(), vardecls[i].sym);
                            }
                        }
                    }
                } finally {
                    inits.assign(initsPrev);
                    uninits.assign(uninitsPrev);
                    nextadr = nextadrPrev;
                    firstadr = firstadrPrev;
                    returnadr = returnadrPrev;
                    isInitialConstructor = lastInitialConstructor;
                }
            } finally {
                lint = lintPrev;
            }
        }

        protected void initParam(JCVariableDecl def) {
            inits.incl(def.sym.adr);
            uninits.excl(def.sym.adr);
        }

        public void visitVarDef(JCVariableDecl tree) {
            Lint lintPrev = lint;
            lint = lint.augment(tree.sym);
            try{
                boolean track = trackable(tree.sym);
                if (track && (tree.sym.owner.kind == MTH || tree.sym.owner.kind == VAR)) {
                    newVar(tree);
                }
                if (tree.init != null) {
                    scanExpr(tree.init);
                    if (track) {
                        letInit(tree.pos(), tree.sym);
                    }
                }
            } finally {
                lint = lintPrev;
            }
        }

        public void visitBlock(JCBlock tree) {
            int nextadrPrev = nextadr;
            scan(tree.stats);
            nextadr = nextadrPrev;
        }

        public void visitDoLoop(JCDoWhileLoop tree) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            FlowKind prevFlowKind = flowKind;
            flowKind = FlowKind.NORMAL;
            final Bits initsSkip = new Bits(true);
            final Bits uninitsSkip = new Bits(true);
            pendingExits = new ListBuffer<>();
            int prevErrors = log.nerrors;
            do {
                final Bits uninitsEntry = new Bits(uninits);
                uninitsEntry.excludeFrom(nextadr);
                scan(tree.body);
                resolveContinues(tree);
                scanCond(tree.cond);
                if (!flowKind.isFinal()) {
                    initsSkip.assign(initsWhenFalse);
                    uninitsSkip.assign(uninitsWhenFalse);
                }
                if (log.nerrors !=  prevErrors ||
                    flowKind.isFinal() ||
                    new Bits(uninitsEntry).diffSet(uninitsWhenTrue).nextBit(firstadr)==-1)
                    break;
                inits.assign(initsWhenTrue);
                uninits.assign(uninitsEntry.andSet(uninitsWhenTrue));
                flowKind = FlowKind.SPECULATIVE_LOOP;
            } while (true);
            flowKind = prevFlowKind;
            inits.assign(initsSkip);
            uninits.assign(uninitsSkip);
            resolveBreaks(tree, prevPendingExits);
        }

        public void visitWhileLoop(JCWhileLoop tree) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            FlowKind prevFlowKind = flowKind;
            flowKind = FlowKind.NORMAL;
            final Bits initsSkip = new Bits(true);
            final Bits uninitsSkip = new Bits(true);
            pendingExits = new ListBuffer<>();
            int prevErrors = log.nerrors;
            final Bits uninitsEntry = new Bits(uninits);
            uninitsEntry.excludeFrom(nextadr);
            do {
                scanCond(tree.cond);
                if (!flowKind.isFinal()) {
                    initsSkip.assign(initsWhenFalse) ;
                    uninitsSkip.assign(uninitsWhenFalse);
                }
                inits.assign(initsWhenTrue);
                uninits.assign(uninitsWhenTrue);
                scan(tree.body);
                resolveContinues(tree);
                if (log.nerrors != prevErrors ||
                    flowKind.isFinal() ||
                    new Bits(uninitsEntry).diffSet(uninits).nextBit(firstadr) == -1) {
                    break;
                }
                uninits.assign(uninitsEntry.andSet(uninits));
                flowKind = FlowKind.SPECULATIVE_LOOP;
            } while (true);
            flowKind = prevFlowKind;
            //a variable is DA/DU after the while statement, if it's DA/DU assuming the
            //branch is not taken AND if it's DA/DU before any break statement
            inits.assign(initsSkip);
            uninits.assign(uninitsSkip);
            resolveBreaks(tree, prevPendingExits);
        }

        public void visitForLoop(JCForLoop tree) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            FlowKind prevFlowKind = flowKind;
            flowKind = FlowKind.NORMAL;
            int nextadrPrev = nextadr;
            scan(tree.init);
            final Bits initsSkip = new Bits(true);
            final Bits uninitsSkip = new Bits(true);
            pendingExits = new ListBuffer<>();
            int prevErrors = log.nerrors;
            do {
                final Bits uninitsEntry = new Bits(uninits);
                uninitsEntry.excludeFrom(nextadr);
                if (tree.cond != null) {
                    scanCond(tree.cond);
                    if (!flowKind.isFinal()) {
                        initsSkip.assign(initsWhenFalse);
                        uninitsSkip.assign(uninitsWhenFalse);
                    }
                    inits.assign(initsWhenTrue);
                    uninits.assign(uninitsWhenTrue);
                } else if (!flowKind.isFinal()) {
                    initsSkip.assign(inits);
                    initsSkip.inclRange(firstadr, nextadr);
                    uninitsSkip.assign(uninits);
                    uninitsSkip.inclRange(firstadr, nextadr);
                }
                scan(tree.body);
                resolveContinues(tree);
                scan(tree.step);
                if (log.nerrors != prevErrors ||
                    flowKind.isFinal() ||
                    new Bits(uninitsEntry).diffSet(uninits).nextBit(firstadr) == -1)
                    break;
                uninits.assign(uninitsEntry.andSet(uninits));
                flowKind = FlowKind.SPECULATIVE_LOOP;
            } while (true);
            flowKind = prevFlowKind;
            //a variable is DA/DU after a for loop, if it's DA/DU assuming the
            //branch is not taken AND if it's DA/DU before any break statement
            inits.assign(initsSkip);
            uninits.assign(uninitsSkip);
            resolveBreaks(tree, prevPendingExits);
            nextadr = nextadrPrev;
        }

        public void visitForeachLoop(JCEnhancedForLoop tree) {
            visitVarDef(tree.var);

            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            FlowKind prevFlowKind = flowKind;
            flowKind = FlowKind.NORMAL;
            int nextadrPrev = nextadr;
            scan(tree.expr);
            final Bits initsStart = new Bits(inits);
            final Bits uninitsStart = new Bits(uninits);

            letInit(tree.pos(), tree.var.sym);
            pendingExits = new ListBuffer<>();
            int prevErrors = log.nerrors;
            do {
                final Bits uninitsEntry = new Bits(uninits);
                uninitsEntry.excludeFrom(nextadr);
                scan(tree.body);
                resolveContinues(tree);
                if (log.nerrors != prevErrors ||
                    flowKind.isFinal() ||
                    new Bits(uninitsEntry).diffSet(uninits).nextBit(firstadr) == -1)
                    break;
                uninits.assign(uninitsEntry.andSet(uninits));
                flowKind = FlowKind.SPECULATIVE_LOOP;
            } while (true);
            flowKind = prevFlowKind;
            inits.assign(initsStart);
            uninits.assign(uninitsStart.andSet(uninits));
            resolveBreaks(tree, prevPendingExits);
            nextadr = nextadrPrev;
        }

        public void visitLabelled(JCLabeledStatement tree) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            pendingExits = new ListBuffer<>();
            scan(tree.body);
            resolveBreaks(tree, prevPendingExits);
        }

        public void visitSwitch(JCSwitch tree) {
            handleSwitch(tree, tree.selector, tree.cases);
        }

        public void visitSwitchExpression(JCSwitchExpression tree) {
            handleSwitch(tree, tree.selector, tree.cases);
        }

        private void handleSwitch(JCTree tree, JCExpression selector, List<JCCase> cases) {
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            pendingExits = new ListBuffer<>();
            int nextadrPrev = nextadr;
            scanExpr(selector);
            final Bits initsSwitch = new Bits(inits);
            final Bits uninitsSwitch = new Bits(uninits);
            boolean hasDefault = false;
            for (List<JCCase> l = cases; l.nonEmpty(); l = l.tail) {
                inits.assign(initsSwitch);
                uninits.assign(uninits.andSet(uninitsSwitch));
                JCCase c = l.head;
                if (c.pats.isEmpty()) {
                    hasDefault = true;
                } else {
                    for (JCExpression pat : c.pats) {
                        scanExpr(pat);
                    }
                }
                if (hasDefault) {
                    inits.assign(initsSwitch);
                    uninits.assign(uninits.andSet(uninitsSwitch));
                }
                scan(c.stats);
                if (c.completesNormally && c.caseKind == JCCase.RULE) {
                    scanSyntheticBreak(make, tree);
                }
                addVars(c.stats, initsSwitch, uninitsSwitch);
                if (!hasDefault) {
                    inits.assign(initsSwitch);
                    uninits.assign(uninits.andSet(uninitsSwitch));
                }
                // Warn about fall-through if lint switch fallthrough enabled.
            }
            if (!hasDefault) {
                if (tree.hasTag(SWITCH_EXPRESSION)) {
                    markDead();
                } else {
                    inits.andSet(initsSwitch);
                }
            }
            if (tree.hasTag(SWITCH_EXPRESSION)) {
                resolveYields(tree, prevPendingExits);
            } else {
                resolveBreaks(tree, prevPendingExits);
            }
            nextadr = nextadrPrev;
        }
        // where
            
Add any variables defined in stats to inits and uninits. /** Add any variables defined in stats to inits and uninits. */
            private void addVars(List<JCStatement> stats, final Bits inits,
                                        final Bits uninits) {
                for (;stats.nonEmpty(); stats = stats.tail) {
                    JCTree stat = stats.head;
                    if (stat.hasTag(VARDEF)) {
                        int adr = ((JCVariableDecl) stat).sym.adr;
                        inits.excl(adr);
                        uninits.incl(adr);
                    }
                }
            }

        public void visitTry(JCTry tree) {
            ListBuffer<JCVariableDecl> resourceVarDecls = new ListBuffer<>();
            final Bits uninitsTryPrev = new Bits(uninitsTry);
            ListBuffer<PendingExit> prevPendingExits = pendingExits;
            pendingExits = new ListBuffer<>();
            final Bits initsTry = new Bits(inits);
            uninitsTry.assign(uninits);
            for (JCTree resource : tree.resources) {
                if (resource instanceof JCVariableDecl) {
                    JCVariableDecl vdecl = (JCVariableDecl) resource;
                    visitVarDef(vdecl);
                    unrefdResources.enter(vdecl.sym);
                    resourceVarDecls.append(vdecl);
                } else if (resource instanceof JCExpression) {
                    scanExpr((JCExpression) resource);
                } else {
                    throw new AssertionError(tree);  // parser error
                }
            }
            scan(tree.body);
            uninitsTry.andSet(uninits);
            final Bits initsEnd = new Bits(inits);
            final Bits uninitsEnd = new Bits(uninits);
            int nextadrCatch = nextadr;

            if (!resourceVarDecls.isEmpty() &&
                    lint.isEnabled(Lint.LintCategory.TRY)) {
                for (JCVariableDecl resVar : resourceVarDecls) {
                    if (unrefdResources.includes(resVar.sym)) {
                        log.warning(Lint.LintCategory.TRY, resVar.pos(),
                                    Warnings.TryResourceNotReferenced(resVar.sym));
                        unrefdResources.remove(resVar.sym);
                    }
                }
            }

            /*  The analysis of each catch should be independent.
             *  Each one should have the same initial values of inits and
             *  uninits.
             */
            final Bits initsCatchPrev = new Bits(initsTry);
            final Bits uninitsCatchPrev = new Bits(uninitsTry);

            for (List<JCCatch> l = tree.catchers; l.nonEmpty(); l = l.tail) {
                JCVariableDecl param = l.head.param;
                inits.assign(initsCatchPrev);
                uninits.assign(uninitsCatchPrev);
                scan(param);
                /* If this is a TWR and we are executing the code from Gen,
                 * then there can be synthetic variables, ignore them.
                 */
                initParam(param);
                scan(l.head.body);
                initsEnd.andSet(inits);
                uninitsEnd.andSet(uninits);
                nextadr = nextadrCatch;
            }
            if (tree.finalizer != null) {
                inits.assign(initsTry);
                uninits.assign(uninitsTry);
                ListBuffer<PendingExit> exits = pendingExits;
                pendingExits = prevPendingExits;
                scan(tree.finalizer);
                if (!tree.finallyCanCompleteNormally) {
                    // discard exits and exceptions from try and finally
                } else {
                    uninits.andSet(uninitsEnd);
                    // FIX: this doesn't preserve source order of exits in catch
                    // versus finally!
                    while (exits.nonEmpty()) {
                        PendingExit exit = exits.next();
                        if (exit instanceof AssignPendingExit) {
                            ((AssignPendingExit) exit).exit_inits.orSet(inits);
                            ((AssignPendingExit) exit).exit_uninits.andSet(uninits);
                        }
                        pendingExits.append(exit);
                    }
                    inits.orSet(initsEnd);
                }
            } else {
                inits.assign(initsEnd);
                uninits.assign(uninitsEnd);
                ListBuffer<PendingExit> exits = pendingExits;
                pendingExits = prevPendingExits;
                while (exits.nonEmpty()) pendingExits.append(exits.next());
            }
            uninitsTry.andSet(uninitsTryPrev).andSet(uninits);
        }

        public void visitConditional(JCConditional tree) {
            scanCond(tree.cond);
            final Bits initsBeforeElse = new Bits(initsWhenFalse);
            final Bits uninitsBeforeElse = new Bits(uninitsWhenFalse);
            inits.assign(initsWhenTrue);
            uninits.assign(uninitsWhenTrue);
            if (tree.truepart.type.hasTag(BOOLEAN) &&
                tree.falsepart.type.hasTag(BOOLEAN)) {
                // if b and c are boolean valued, then
                // v is (un)assigned after a?b:c when true iff
                //    v is (un)assigned after b when true and
                //    v is (un)assigned after c when true
                scanCond(tree.truepart);
                final Bits initsAfterThenWhenTrue = new Bits(initsWhenTrue);
                final Bits initsAfterThenWhenFalse = new Bits(initsWhenFalse);
                final Bits uninitsAfterThenWhenTrue = new Bits(uninitsWhenTrue);
                final Bits uninitsAfterThenWhenFalse = new Bits(uninitsWhenFalse);
                inits.assign(initsBeforeElse);
                uninits.assign(uninitsBeforeElse);
                scanCond(tree.falsepart);
                initsWhenTrue.andSet(initsAfterThenWhenTrue);
                initsWhenFalse.andSet(initsAfterThenWhenFalse);
                uninitsWhenTrue.andSet(uninitsAfterThenWhenTrue);
                uninitsWhenFalse.andSet(uninitsAfterThenWhenFalse);
            } else {
                scanExpr(tree.truepart);
                final Bits initsAfterThen = new Bits(inits);
                final Bits uninitsAfterThen = new Bits(uninits);
                inits.assign(initsBeforeElse);
                uninits.assign(uninitsBeforeElse);
                scanExpr(tree.falsepart);
                inits.andSet(initsAfterThen);
                uninits.andSet(uninitsAfterThen);
            }
        }

        public void visitIf(JCIf tree) {
            scanCond(tree.cond);
            final Bits initsBeforeElse = new Bits(initsWhenFalse);
            final Bits uninitsBeforeElse = new Bits(uninitsWhenFalse);
            inits.assign(initsWhenTrue);
            uninits.assign(uninitsWhenTrue);
            scan(tree.thenpart);
            if (tree.elsepart != null) {
                final Bits initsAfterThen = new Bits(inits);
                final Bits uninitsAfterThen = new Bits(uninits);
                inits.assign(initsBeforeElse);
                uninits.assign(uninitsBeforeElse);
                scan(tree.elsepart);
                inits.andSet(initsAfterThen);
                uninits.andSet(uninitsAfterThen);
            } else {
                inits.andSet(initsBeforeElse);
                uninits.andSet(uninitsBeforeElse);
            }
        }

        @Override
        public void visitBreak(JCBreak tree) {
            recordExit(new AssignPendingExit(tree, inits, uninits));
        }

        @Override
        public void visitYield(JCYield tree) {
            JCSwitchExpression expr = (JCSwitchExpression) tree.target;
            if (expr != null && expr.type.hasTag(BOOLEAN)) {
                scanCond(tree.value);
                Bits initsAfterBreakWhenTrue = new Bits(initsWhenTrue);
                Bits initsAfterBreakWhenFalse = new Bits(initsWhenFalse);
                Bits uninitsAfterBreakWhenTrue = new Bits(uninitsWhenTrue);
                Bits uninitsAfterBreakWhenFalse = new Bits(uninitsWhenFalse);
                PendingExit exit = new PendingExit(tree) {
                    @Override
                    void resolveJump() {
                        if (!inits.isReset()) {
                            split(true);
                        }
                        initsWhenTrue.andSet(initsAfterBreakWhenTrue);
                        initsWhenFalse.andSet(initsAfterBreakWhenFalse);
                        uninitsWhenTrue.andSet(uninitsAfterBreakWhenTrue);
                        uninitsWhenFalse.andSet(uninitsAfterBreakWhenFalse);
                    }
                };
                merge();
                recordExit(exit);
                return ;
            } else {
                scanExpr(tree.value);
                recordExit(new AssignPendingExit(tree, inits, uninits));
            }
        }

        @Override
        public void visitContinue(JCContinue tree) {
            recordExit(new AssignPendingExit(tree, inits, uninits));
        }

        @Override
        public void visitReturn(JCReturn tree) {
            scanExpr(tree.expr);
            recordExit(new AssignPendingExit(tree, inits, uninits));
        }

        public void visitThrow(JCThrow tree) {
            scanExpr(tree.expr);
            markDead();
        }

        public void visitApply(JCMethodInvocation tree) {
            scanExpr(tree.meth);
            scanExprs(tree.args);
        }

        public void visitNewClass(JCNewClass tree) {
            scanExpr(tree.encl);
            scanExprs(tree.args);
            scan(tree.def);
        }

        @Override
        public void visitLambda(JCLambda tree) {
            final Bits prevUninits = new Bits(uninits);
            final Bits prevInits = new Bits(inits);
            int returnadrPrev = returnadr;
            int nextadrPrev = nextadr;
            ListBuffer<PendingExit> prevPending = pendingExits;
            try {
                returnadr = nextadr;
                pendingExits = new ListBuffer<>();
                for (List<JCVariableDecl> l = tree.params; l.nonEmpty(); l = l.tail) {
                    JCVariableDecl def = l.head;
                    scan(def);
                    inits.incl(def.sym.adr);
                    uninits.excl(def.sym.adr);
                }
                if (tree.getBodyKind() == JCLambda.BodyKind.EXPRESSION) {
                    scanExpr(tree.body);
                } else {
                    scan(tree.body);
                }
            }
            finally {
                returnadr = returnadrPrev;
                uninits.assign(prevUninits);
                inits.assign(prevInits);
                pendingExits = prevPending;
                nextadr = nextadrPrev;
            }
        }

        public void visitNewArray(JCNewArray tree) {
            scanExprs(tree.dims);
            scanExprs(tree.elems);
        }

        public void visitAssert(JCAssert tree) {
            final Bits initsExit = new Bits(inits);
            final Bits uninitsExit = new Bits(uninits);
            scanCond(tree.cond);
            uninitsExit.andSet(uninitsWhenTrue);
            if (tree.detail != null) {
                inits.assign(initsWhenFalse);
                uninits.assign(uninitsWhenFalse);
                scanExpr(tree.detail);
            }
            inits.assign(initsExit);
            uninits.assign(uninitsExit);
        }

        public void visitAssign(JCAssign tree) {
            if (!TreeInfo.isIdentOrThisDotIdent(tree.lhs))
                scanExpr(tree.lhs);
            scanExpr(tree.rhs);
            letInit(tree.lhs);
        }

        // check fields accessed through this.<field> are definitely
        // assigned before reading their value
        public void visitSelect(JCFieldAccess tree) {
            super.visitSelect(tree);
            if (TreeInfo.isThisQualifier(tree.selected) &&
                tree.sym.kind == VAR) {
                checkInit(tree.pos(), (VarSymbol)tree.sym);
            }
        }

        public void visitAssignop(JCAssignOp tree) {
            scanExpr(tree.lhs);
            scanExpr(tree.rhs);
            letInit(tree.lhs);
        }

        public void visitUnary(JCUnary tree) {
            switch (tree.getTag()) {
            case NOT:
                scanCond(tree.arg);
                final Bits t = new Bits(initsWhenFalse);
                initsWhenFalse.assign(initsWhenTrue);
                initsWhenTrue.assign(t);
                t.assign(uninitsWhenFalse);
                uninitsWhenFalse.assign(uninitsWhenTrue);
                uninitsWhenTrue.assign(t);
                break;
            case PREINC: case POSTINC:
            case PREDEC: case POSTDEC:
                scanExpr(tree.arg);
                letInit(tree.arg);
                break;
            default:
                scanExpr(tree.arg);
            }
        }

        public void visitBinary(JCBinary tree) {
            switch (tree.getTag()) {
            case AND:
                scanCond(tree.lhs);
                final Bits initsWhenFalseLeft = new Bits(initsWhenFalse);
                final Bits uninitsWhenFalseLeft = new Bits(uninitsWhenFalse);
                inits.assign(initsWhenTrue);
                uninits.assign(uninitsWhenTrue);
                scanCond(tree.rhs);
                initsWhenFalse.andSet(initsWhenFalseLeft);
                uninitsWhenFalse.andSet(uninitsWhenFalseLeft);
                break;
            case OR:
                scanCond(tree.lhs);
                final Bits initsWhenTrueLeft = new Bits(initsWhenTrue);
                final Bits uninitsWhenTrueLeft = new Bits(uninitsWhenTrue);
                inits.assign(initsWhenFalse);
                uninits.assign(uninitsWhenFalse);
                scanCond(tree.rhs);
                initsWhenTrue.andSet(initsWhenTrueLeft);
                uninitsWhenTrue.andSet(uninitsWhenTrueLeft);
                break;
            default:
                scanExpr(tree.lhs);
                scanExpr(tree.rhs);
            }
        }

        public void visitIdent(JCIdent tree) {
            if (tree.sym.kind == VAR) {
                checkInit(tree.pos(), (VarSymbol)tree.sym);
                referenced(tree.sym);
            }
        }

        void referenced(Symbol sym) {
            unrefdResources.remove(sym);
        }

        public void visitAnnotatedType(JCAnnotatedType tree) {
            // annotations don't get scanned
            tree.underlyingType.accept(this);
        }

        public void visitModuleDef(JCModuleDecl tree) {
            // Do nothing for modules
        }

    /**************************************************************************
     * main method
     *************************************************************************/

        
Perform definite assignment/unassignment analysis on a tree.
/** Perform definite assignment/unassignment analysis on a tree.
         */
        public void analyzeTree(Env<?> env, TreeMaker make) {
            analyzeTree(env, env.tree, make);
         }

        public void analyzeTree(Env<?> env, JCTree tree, TreeMaker make) {
            try {
                startPos = tree.pos().getStartPosition();

                if (vardecls == null)
                    vardecls = new JCVariableDecl[32];
                else
                    for (int i=0; i<vardecls.length; i++)
                        vardecls[i] = null;
                firstadr = 0;
                nextadr = 0;
                Flow.this.make = make;
                pendingExits = new ListBuffer<>();
                this.classDef = null;
                unrefdResources = WriteableScope.create(env.enclClass.sym);
                scan(tree);
            } finally {
                // note that recursive invocations of this method fail hard
                startPos = -1;
                resetBits(inits, uninits, uninitsTry, initsWhenTrue,
                        initsWhenFalse, uninitsWhenTrue, uninitsWhenFalse);
                if (vardecls != null) {
                    for (int i=0; i<vardecls.length; i++)
                        vardecls[i] = null;
                }
                firstadr = 0;
                nextadr = 0;
                Flow.this.make = null;
                pendingExits = null;
                this.classDef = null;
                unrefdResources = null;
            }
        }
    }

    
This pass implements the last step of the dataflow analysis, namely
the effectively-final analysis check. This checks that every local variable
reference from a lambda body/local inner class is either final or effectively final.
Additional this also checks that every variable that is used as an operand to
try-with-resources is final or effectively final.
As effectively final variables are marked as such during DA/DU, this pass must run after
AssignAnalyzer.
/**
     * This pass implements the last step of the dataflow analysis, namely
     * the effectively-final analysis check. This checks that every local variable
     * reference from a lambda body/local inner class is either final or effectively final.
     * Additional this also checks that every variable that is used as an operand to
     * try-with-resources is final or effectively final.
     * As effectively final variables are marked as such during DA/DU, this pass must run after
     * AssignAnalyzer.
     */
    class CaptureAnalyzer extends BaseAnalyzer {

        JCTree currentTree; //local class or lambda

        @Override
        void markDead() {
            //do nothing
        }

        @SuppressWarnings("fallthrough")
        void checkEffectivelyFinal(DiagnosticPosition pos, VarSymbol sym) {
            if (currentTree != null &&
                    sym.owner.kind == MTH &&
                    sym.pos < currentTree.getStartPosition()) {
                switch (currentTree.getTag()) {
                    case CLASSDEF:
                        if (!allowEffectivelyFinalInInnerClasses) {
                            if ((sym.flags() & FINAL) == 0) {
                                reportInnerClsNeedsFinalError(pos, sym);
                            }
                            break;
                        }
                    case LAMBDA:
                        if ((sym.flags() & (EFFECTIVELY_FINAL | FINAL)) == 0) {
                           reportEffectivelyFinalError(pos, sym);
                        }
                }
            }
        }

        @SuppressWarnings("fallthrough")
        void letInit(JCTree tree) {
            tree = TreeInfo.skipParens(tree);
            if (tree.hasTag(IDENT) || tree.hasTag(SELECT)) {
                Symbol sym = TreeInfo.symbol(tree);
                if (currentTree != null &&
                        sym.kind == VAR &&
                        sym.owner.kind == MTH &&
                        ((VarSymbol)sym).pos < currentTree.getStartPosition()) {
                    switch (currentTree.getTag()) {
                        case CLASSDEF:
                            if (!allowEffectivelyFinalInInnerClasses) {
                                reportInnerClsNeedsFinalError(tree, sym);
                                break;
                            }
                        case LAMBDA:
                            reportEffectivelyFinalError(tree, sym);
                    }
                }
            }
        }

        void reportEffectivelyFinalError(DiagnosticPosition pos, Symbol sym) {
            String subKey = currentTree.hasTag(LAMBDA) ?
                  "lambda"  : "inner.cls";
            log.error(pos, Errors.CantRefNonEffectivelyFinalVar(sym, diags.fragment(subKey)));
        }

        void reportInnerClsNeedsFinalError(DiagnosticPosition pos, Symbol sym) {
            log.error(pos,
                      Errors.LocalVarAccessedFromIclsNeedsFinal(sym));
        }

    
Visitor methods for statements and definitions
/*************************************************************************
     * Visitor methods for statements and definitions
     *************************************************************************/

        /* ------------ Visitor methods for various sorts of trees -------------*/

        public void visitClassDef(JCClassDecl tree) {
            JCTree prevTree = currentTree;
            try {
                currentTree = tree.sym.isLocal() ? tree : null;
                super.visitClassDef(tree);
            } finally {
                currentTree = prevTree;
            }
        }

        @Override
        public void visitLambda(JCLambda tree) {
            JCTree prevTree = currentTree;
            try {
                currentTree = tree;
                super.visitLambda(tree);
            } finally {
                currentTree = prevTree;
            }
        }

        @Override
        public void visitIdent(JCIdent tree) {
            if (tree.sym.kind == VAR) {
                checkEffectivelyFinal(tree, (VarSymbol)tree.sym);
            }
        }

        public void visitAssign(JCAssign tree) {
            JCTree lhs = TreeInfo.skipParens(tree.lhs);
            if (!(lhs instanceof JCIdent)) {
                scan(lhs);
            }
            scan(tree.rhs);
            letInit(lhs);
        }

        public void visitAssignop(JCAssignOp tree) {
            scan(tree.lhs);
            scan(tree.rhs);
            letInit(tree.lhs);
        }

        public void visitUnary(JCUnary tree) {
            switch (tree.getTag()) {
                case PREINC: case POSTINC:
                case PREDEC: case POSTDEC:
                    scan(tree.arg);
                    letInit(tree.arg);
                    break;
                default:
                    scan(tree.arg);
            }
        }

        public void visitTry(JCTry tree) {
            for (JCTree resource : tree.resources) {
                if (!resource.hasTag(VARDEF)) {
                    Symbol var = TreeInfo.symbol(resource);
                    if (var != null && (var.flags() & (FINAL | EFFECTIVELY_FINAL)) == 0) {
                        log.error(resource.pos(), Errors.TryWithResourcesExprEffectivelyFinalVar(var));
                    }
                }
            }
            super.visitTry(tree);
        }

        @Override
        public void visitYield(JCYield tree) {
            scan(tree.value);
        }

        public void visitModuleDef(JCModuleDecl tree) {
            // Do nothing for modules
        }

    /**************************************************************************
     * main method
     *************************************************************************/

        
Perform definite assignment/unassignment analysis on a tree.
/** Perform definite assignment/unassignment analysis on a tree.
         */
        public void analyzeTree(Env<AttrContext> env, TreeMaker make) {
            analyzeTree(env, env.tree, make);
        }
        public void analyzeTree(Env<AttrContext> env, JCTree tree, TreeMaker make) {
            try {
                attrEnv = env;
                Flow.this.make = make;
                pendingExits = new ListBuffer<>();
                scan(tree);
            } finally {
                pendingExits = null;
                Flow.this.make = null;
            }
        }
    }

    enum Liveness {
        ALIVE {
            @Override
            public Liveness or(Liveness other) {
                return this;
            }
            @Override
            public Liveness and(Liveness other) {
                return other;
            }
        },
        DEAD {
            @Override
            public Liveness or(Liveness other) {
                return other;
            }
            @Override
            public Liveness and(Liveness other) {
                return this;
            }
        },
        RECOVERY {
            @Override
            public Liveness or(Liveness other) {
                if (other == ALIVE) {
                    return ALIVE;
                } else {
                    return this;
                }
            }
            @Override
            public Liveness and(Liveness other) {
                if (other == DEAD) {
                    return DEAD;
                } else {
                    return this;
                }
            }
        };

        public abstract Liveness or(Liveness other);
        public abstract Liveness and(Liveness other);
        public Liveness or(boolean value) {
            return or(from(value));
        }
        public Liveness and(boolean value) {
            return and(from(value));
        }
        public static Liveness from(boolean value) {
            return value ? ALIVE : DEAD;
        }
    }

}