/*
 * Copyright (c) 2015, 2019, 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.
 */

package com.sun.tools.javac.comp;

import com.sun.tools.javac.code.Flags;
import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.code.Symtab;
import com.sun.tools.javac.code.Type;
import com.sun.tools.javac.code.Types.FunctionDescriptorLookupError;
import com.sun.tools.javac.comp.Attr.ResultInfo;
import com.sun.tools.javac.comp.Attr.TargetInfo;
import com.sun.tools.javac.comp.Check.CheckContext;
import com.sun.tools.javac.comp.DeferredAttr.AttrMode;
import com.sun.tools.javac.comp.DeferredAttr.DeferredAttrContext;
import com.sun.tools.javac.comp.DeferredAttr.DeferredType;
import com.sun.tools.javac.comp.DeferredAttr.DeferredTypeCompleter;
import com.sun.tools.javac.comp.DeferredAttr.LambdaReturnScanner;
import com.sun.tools.javac.comp.DeferredAttr.SwitchExpressionScanner;
import com.sun.tools.javac.comp.Infer.PartiallyInferredMethodType;
import com.sun.tools.javac.comp.Resolve.MethodResolutionPhase;
import com.sun.tools.javac.resources.CompilerProperties.Fragments;
import com.sun.tools.javac.tree.JCTree;
import com.sun.tools.javac.tree.JCTree.JCConditional;
import com.sun.tools.javac.tree.JCTree.JCExpression;
import com.sun.tools.javac.tree.JCTree.JCLambda;
import com.sun.tools.javac.tree.JCTree.JCLambda.ParameterKind;
import com.sun.tools.javac.tree.JCTree.JCMemberReference;
import com.sun.tools.javac.tree.JCTree.JCMethodInvocation;
import com.sun.tools.javac.tree.JCTree.JCNewClass;
import com.sun.tools.javac.tree.JCTree.JCParens;
import com.sun.tools.javac.tree.JCTree.JCReturn;
import com.sun.tools.javac.tree.JCTree.JCSwitchExpression;
import com.sun.tools.javac.tree.TreeCopier;
import com.sun.tools.javac.tree.TreeInfo;
import com.sun.tools.javac.util.Assert;
import com.sun.tools.javac.util.Context;
import com.sun.tools.javac.util.DiagnosticSource;
import com.sun.tools.javac.util.JCDiagnostic;
import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
import com.sun.tools.javac.util.List;
import com.sun.tools.javac.util.ListBuffer;
import com.sun.tools.javac.util.Log;

import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Optional;
import java.util.function.Function;
import java.util.function.Supplier;

import static com.sun.tools.javac.code.TypeTag.ARRAY;
import static com.sun.tools.javac.code.TypeTag.DEFERRED;
import static com.sun.tools.javac.code.TypeTag.FORALL;
import static com.sun.tools.javac.code.TypeTag.METHOD;
import static com.sun.tools.javac.code.TypeTag.VOID;
import com.sun.tools.javac.tree.JCTree.JCYield;

This class performs attribution of method/constructor arguments when target-typing is enabled (source >= 8); for each argument that is potentially a poly expression, this class builds a rich representation (see ArgumentType which can then be used for performing fast overload checks without requiring multiple attribution passes over the same code. The attribution strategy for a given method/constructor argument A is as follows: - if A is potentially a poly expression (i.e. diamond instance creation expression), a speculative pass over A is performed; the results of such speculative attribution are then saved in a special type, so that enclosing overload resolution can be carried by simply checking compatibility against the type determined during this speculative pass. - if A is a standalone expression, regular attribution takes place. To minimize the speculative work, a cache is used, so that already computed argument types associated with a given unique source location are never recomputed multiple times. /**
 * This class performs attribution of method/constructor arguments when target-typing is enabled
 * (source >= 8); for each argument that is potentially a poly expression, this class builds
 * a rich representation (see {@link ArgumentType} which can then be used for performing fast overload
 * checks without requiring multiple attribution passes over the same code.
 *
 * The attribution strategy for a given method/constructor argument A is as follows:
 *
 * - if A is potentially a poly expression (i.e. diamond instance creation expression), a speculative
 * pass over A is performed; the results of such speculative attribution are then saved in a special
 * type, so that enclosing overload resolution can be carried by simply checking compatibility against the
 * type determined during this speculative pass.
 *
 * - if A is a standalone expression, regular attribution takes place.
 *
 * To minimize the speculative work, a cache is used, so that already computed argument types
 * associated with a given unique source location are never recomputed multiple times.
 */
public class ArgumentAttr extends JCTree.Visitor {

    protected static final Context.Key<ArgumentAttr> methodAttrKey = new Context.Key<>();

    private final DeferredAttr deferredAttr;
    private final JCDiagnostic.Factory diags;
    private final Attr attr;
    private final Symtab syms;
    private final Log log;

    
Attribution environment to be used. /** Attribution environment to be used. */
    private Env<AttrContext> env;

    
Result of method attribution. /** Result of method attribution. */
    Type result;

    
Cache for argument types; behavior is influenced by the currently selected cache policy. /** Cache for argument types; behavior is influenced by the currently selected cache policy. */
    Map<UniquePos, ArgumentType<?>> argumentTypeCache = new LinkedHashMap<>();

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

    protected ArgumentAttr(Context context) {
        context.put(methodAttrKey, this);
        deferredAttr = DeferredAttr.instance(context);
        diags = JCDiagnostic.Factory.instance(context);
        attr = Attr.instance(context);
        syms = Symtab.instance(context);
        log = Log.instance(context);
    }

    
Set the results of method attribution.
/**
     * Set the results of method attribution.
     */
    void setResult(JCExpression tree, Type type) {
        result = type;
        if (env.info.attributionMode == DeferredAttr.AttributionMode.SPECULATIVE) {
            //if we are in a speculative branch we can save the type in the tree itself
            //as there's no risk of polluting the original tree.
            tree.type = result;
        }
    }

    
Checks a type in the speculative tree against a given result; the type can be either a plain
type or an argument type,in which case a more complex check is required.
/**
     * Checks a type in the speculative tree against a given result; the type can be either a plain
     * type or an argument type,in which case a more complex check is required.
     */
    Type checkSpeculative(JCTree expr, ResultInfo resultInfo) {
        return checkSpeculative(expr, expr.type, resultInfo);
    }

    
Checks a type in the speculative tree against a given result; the type can be either a plain
type or an argument type,in which case a more complex check is required.
/**
     * Checks a type in the speculative tree against a given result; the type can be either a plain
     * type or an argument type,in which case a more complex check is required.
     */
    Type checkSpeculative(DiagnosticPosition pos, Type t, ResultInfo resultInfo) {
        if (t.hasTag(DEFERRED)) {
            return ((DeferredType)t).check(resultInfo);
        } else {
            return resultInfo.check(pos, t);
        }
    }

    
Returns a local caching context in which argument types can safely be cached without
the risk of polluting enclosing contexts. This is useful when attempting speculative
attribution of potentially erroneous expressions, which could end up polluting the cache.
/**
     * Returns a local caching context in which argument types can safely be cached without
     * the risk of polluting enclosing contexts. This is useful when attempting speculative
     * attribution of potentially erroneous expressions, which could end up polluting the cache.
     */
    LocalCacheContext withLocalCacheContext() {
        return new LocalCacheContext();
    }

    
Local cache context; this class keeps track of the previous cache and reverts to it when the leave() method is called. /**
     * Local cache context; this class keeps track of the previous cache and reverts to it
     * when the {@link LocalCacheContext#leave()} method is called.
     */
    class LocalCacheContext {
        Map<UniquePos, ArgumentType<?>> prevCache;

        public LocalCacheContext() {
            this.prevCache = argumentTypeCache;
            argumentTypeCache = new HashMap<>();
        }

        public void leave() {
            argumentTypeCache = prevCache;
        }
    }

    
Main entry point for attributing an argument with given tree and attribution environment.
/**
     * Main entry point for attributing an argument with given tree and attribution environment.
     */
    Type attribArg(JCTree tree, Env<AttrContext> env) {
        Env<AttrContext> prevEnv = this.env;
        try {
            this.env = env;
            tree.accept(this);
            return result;
        } finally {
            this.env = prevEnv;
        }
    }

    @Override
    public void visitTree(JCTree that) {
        //delegates to Attr
        that.accept(attr);
        result = attr.result;
    }

    
Process a method argument; this method takes care of performing a speculative pass over the
argument tree and calling a well-defined entry point to build the argument type associated
with such tree.
/**
     * Process a method argument; this method takes care of performing a speculative pass over the
     * argument tree and calling a well-defined entry point to build the argument type associated
     * with such tree.
     */
    @SuppressWarnings("unchecked")
    <T extends JCExpression, Z extends ArgumentType<T>> void processArg(T that, Function<T, Z> argumentTypeFactory) {
        UniquePos pos = new UniquePos(that);
        processArg(that, () -> {
            T speculativeTree = (T)deferredAttr.attribSpeculative(that, env, attr.new MethodAttrInfo() {
                @Override
                protected boolean needsArgumentAttr(JCTree tree) {
                    return !new UniquePos(tree).equals(pos);
                }
            });
            return argumentTypeFactory.apply(speculativeTree);
        });
    }

    
Process a method argument; this method allows the caller to specify a custom speculative attribution
logic (this is used e.g. for lambdas).
/**
     * Process a method argument; this method allows the caller to specify a custom speculative attribution
     * logic (this is used e.g. for lambdas).
     */
    @SuppressWarnings("unchecked")
    <T extends JCExpression, Z extends ArgumentType<T>> void processArg(T that, Supplier<Z> argumentTypeFactory) {
        UniquePos pos = new UniquePos(that);
        Z cached = (Z)argumentTypeCache.get(pos);
        if (cached != null) {
            //dup existing speculative type
            setResult(that, cached.dup(that, env));
        } else {
            Z res = argumentTypeFactory.get();
            argumentTypeCache.put(pos, res);
            setResult(that, res);
        }
    }

    @Override
    public void visitParens(JCParens that) {
        processArg(that, speculativeTree -> new ParensType(that, env, speculativeTree));
    }

    @Override
    public void visitConditional(JCConditional that) {
        processArg(that, speculativeTree -> new ConditionalType(that, env, speculativeTree));
    }

    @Override
    public void visitSwitchExpression(JCSwitchExpression that) {
        processArg(that, speculativeTree -> new SwitchExpressionType(that, env, speculativeTree));
    }

    @Override
    public void visitReference(JCMemberReference tree) {
        //perform arity-based check
        Env<AttrContext> localEnv = env.dup(tree);
        JCExpression exprTree;
        exprTree = (JCExpression)deferredAttr.attribSpeculative(tree.getQualifierExpression(), localEnv,
                attr.memberReferenceQualifierResult(tree),
                withLocalCacheContext());
        JCMemberReference mref2 = new TreeCopier<Void>(attr.make).copy(tree);
        mref2.expr = exprTree;
        Symbol lhsSym = TreeInfo.symbol(exprTree);
        localEnv.info.selectSuper = lhsSym != null && lhsSym.name == lhsSym.name.table.names._super;
        Symbol res =
                attr.rs.getMemberReference(tree, localEnv, mref2,
                        exprTree.type, tree.name);
        if (!res.kind.isResolutionError()) {
            tree.sym = res;
        }
        if (res.kind.isResolutionTargetError()) {
             tree.setOverloadKind(JCMemberReference.OverloadKind.ERROR);
        } else if (res.type != null && res.type.hasTag(FORALL) ||
                (res.flags() & Flags.VARARGS) != 0 ||
                (TreeInfo.isStaticSelector(exprTree, tree.name.table.names) &&
                exprTree.type.isRaw() && !exprTree.type.hasTag(ARRAY))) {
            tree.setOverloadKind(JCMemberReference.OverloadKind.OVERLOADED);
        } else {
            tree.setOverloadKind(JCMemberReference.OverloadKind.UNOVERLOADED);
        }
        //return a plain old deferred type for this
        setResult(tree, deferredAttr.new DeferredType(tree, env));
    }

    @Override
    public void visitLambda(JCLambda that) {
        if (that.paramKind == ParameterKind.EXPLICIT) {
            //if lambda is explicit, we can save info in the corresponding argument type
            processArg(that, () -> {
                JCLambda speculativeLambda =
                        deferredAttr.attribSpeculativeLambda(that, env, attr.methodAttrInfo);
                return new ExplicitLambdaType(that, env, speculativeLambda);
            });
        } else {
            //otherwise just use a deferred type
            setResult(that, deferredAttr.new DeferredType(that, env));
        }
    }

    @Override
    public void visitApply(JCMethodInvocation that) {
        if (that.getTypeArguments().isEmpty()) {
            processArg(that, speculativeTree -> new ResolvedMethodType(that, env, speculativeTree));
        } else {
            //not a poly expression, just call Attr
            setResult(that, attr.attribTree(that, env, attr.unknownExprInfo));
        }
    }

    @Override
    public void visitNewClass(JCNewClass that) {
        if (TreeInfo.isDiamond(that)) {
            processArg(that, speculativeTree -> new ResolvedConstructorType(that, env, speculativeTree));
        } else {
            //not a poly expression, just call Attr
            setResult(that, attr.attribTree(that, env, attr.unknownExprInfo));
        }
    }

    
An argument type is similar to a plain deferred type; the most important difference is that
the completion logic associated with argument types allows speculative attribution to be skipped
during overload resolution - that is, an argument type always has enough information to
perform an overload check without the need of calling back to Attr. This extra information
is typically stored in the form of a speculative tree.
/**
     * An argument type is similar to a plain deferred type; the most important difference is that
     * the completion logic associated with argument types allows speculative attribution to be skipped
     * during overload resolution - that is, an argument type always has enough information to
     * perform an overload check without the need of calling back to Attr. This extra information
     * is typically stored in the form of a speculative tree.
     */
    abstract class ArgumentType<T extends JCExpression> extends DeferredType implements DeferredTypeCompleter {

        
The speculative tree carrying type information. /** The speculative tree carrying type information. */
        T speculativeTree;

        
Types associated with this argument (one type per possible target result). /** Types associated with this argument (one type per possible target result). */
        Map<ResultInfo, Type> speculativeTypes;

        public ArgumentType(JCExpression tree, Env<AttrContext> env, T speculativeTree, Map<ResultInfo, Type> speculativeTypes) {
            deferredAttr.super(tree, env);
            this.speculativeTree = speculativeTree;
            this.speculativeTypes = speculativeTypes;
        }

        @Override
        final DeferredTypeCompleter completer() {
            return this;
        }

        @Override
        final public Type complete(DeferredType dt, ResultInfo resultInfo, DeferredAttrContext deferredAttrContext) {
            Assert.check(dt == this);
            if (deferredAttrContext.mode == AttrMode.SPECULATIVE) {
                Type t = (resultInfo.pt == Type.recoveryType) ?
                        deferredAttr.basicCompleter.complete(dt, resultInfo, deferredAttrContext) :
                        overloadCheck(resultInfo, deferredAttrContext);
                speculativeTypes.put(resultInfo, t);
                return t;
            } else {
                if (!env.info.attributionMode.isSpeculative) {
                    argumentTypeCache.remove(new UniquePos(dt.tree));
                }
                return deferredAttr.basicCompleter.complete(dt, resultInfo, deferredAttrContext);
            }
        }

        @Override
        Type speculativeType(Symbol msym, MethodResolutionPhase phase) {
            if (notPertinentToApplicability.contains(msym)) {
                return super.speculativeType(msym, phase);
            } else {
                for (Map.Entry<ResultInfo, Type> _entry : speculativeTypes.entrySet()) {
                    DeferredAttrContext deferredAttrContext = _entry.getKey().checkContext.deferredAttrContext();
                    if (deferredAttrContext.phase == phase && deferredAttrContext.msym == msym) {
                        return _entry.getValue();
                    }
                }
                return Type.noType;
            }
        }

        @Override
        JCTree speculativeTree(DeferredAttrContext deferredAttrContext) {
            return notPertinentToApplicability.contains(deferredAttrContext.msym) ?
                    super.speculativeTree(deferredAttrContext) :
                    speculativeTree;
        }

        
Performs an overload check against a given target result.
/**
         * Performs an overload check against a given target result.
         */
        abstract Type overloadCheck(ResultInfo resultInfo, DeferredAttrContext deferredAttrContext);

        
Creates a copy of this argument type with given tree and environment.
/**
         * Creates a copy of this argument type with given tree and environment.
         */
        abstract ArgumentType<T> dup(T tree, Env<AttrContext> env);
    }

    
Argument type for parenthesized expression.
/**
     * Argument type for parenthesized expression.
     */
    class ParensType extends ArgumentType<JCParens> {
        ParensType(JCExpression tree, Env<AttrContext> env, JCParens speculativeParens) {
            this(tree, env, speculativeParens, new HashMap<>());
        }

        ParensType(JCExpression tree, Env<AttrContext> env, JCParens speculativeParens, Map<ResultInfo, Type> speculativeTypes) {
           super(tree, env, speculativeParens, speculativeTypes);
        }

        @Override
        Type overloadCheck(ResultInfo resultInfo, DeferredAttrContext deferredAttrContext) {
            return checkSpeculative(speculativeTree.expr, resultInfo);
        }

        @Override
        ArgumentType<JCParens> dup(JCParens tree, Env<AttrContext> env) {
            return new ParensType(tree, env, speculativeTree, speculativeTypes);
        }
    }

    
Argument type for conditionals.
/**
     * Argument type for conditionals.
     */
    class ConditionalType extends ArgumentType<JCConditional> {
        ConditionalType(JCExpression tree, Env<AttrContext> env, JCConditional speculativeCond) {
            this(tree, env, speculativeCond, new HashMap<>());
        }

        ConditionalType(JCExpression tree, Env<AttrContext> env, JCConditional speculativeCond, Map<ResultInfo, Type> speculativeTypes) {
           super(tree, env, speculativeCond, speculativeTypes);
        }

        @Override
        Type overloadCheck(ResultInfo resultInfo, DeferredAttrContext deferredAttrContext) {
            ResultInfo localInfo = resultInfo.dup(attr.conditionalContext(resultInfo.checkContext));
            if (speculativeTree.isStandalone()) {
                return localInfo.check(speculativeTree, speculativeTree.type);
            } else if (resultInfo.pt.hasTag(VOID)) {
                //this means we are returning a poly conditional from void-compatible lambda expression
                resultInfo.checkContext.report(tree, attr.diags.fragment(Fragments.ConditionalTargetCantBeVoid));
                return attr.types.createErrorType(resultInfo.pt);
            } else {
                //poly
                checkSpeculative(speculativeTree.truepart, localInfo);
                checkSpeculative(speculativeTree.falsepart, localInfo);
                return localInfo.pt;
            }
        }

        @Override
        ArgumentType<JCConditional> dup(JCConditional tree, Env<AttrContext> env) {
            return new ConditionalType(tree, env, speculativeTree, speculativeTypes);
        }
    }

    
Argument type for switch expressions.
/**
     * Argument type for switch expressions.
     */
    class SwitchExpressionType extends ArgumentType<JCSwitchExpression> {
        
List of break expressions (lazily populated). /** List of break expressions (lazily populated). */
        Optional<List<JCYield>> yieldExpressions = Optional.empty();

        SwitchExpressionType(JCExpression tree, Env<AttrContext> env, JCSwitchExpression speculativeCond) {
            this(tree, env, speculativeCond, new HashMap<>());
        }

        SwitchExpressionType(JCExpression tree, Env<AttrContext> env, JCSwitchExpression speculativeCond, Map<ResultInfo, Type> speculativeTypes) {
           super(tree, env, speculativeCond, speculativeTypes);
        }

        @Override
        Type overloadCheck(ResultInfo resultInfo, DeferredAttrContext deferredAttrContext) {
            ResultInfo localInfo = resultInfo.dup(attr.conditionalContext(resultInfo.checkContext));
            if (resultInfo.pt.hasTag(VOID)) {
                //this means we are returning a poly switch expression from void-compatible lambda expression
                resultInfo.checkContext.report(tree, attr.diags.fragment(Fragments.SwitchExpressionTargetCantBeVoid));
                return attr.types.createErrorType(resultInfo.pt);
            } else {
                //poly
                for (JCYield brk : yieldExpressions()) {
                    checkSpeculative(brk.value, brk.value.type, resultInfo);
                }
                return localInfo.pt;
            }
        }

        
Compute return expressions (if needed). /** Compute return expressions (if needed). */
        List<JCYield> yieldExpressions() {
            return yieldExpressions.orElseGet(() -> {
                final List<JCYield> res;
                ListBuffer<JCYield> buf = new ListBuffer<>();
                new SwitchExpressionScanner() {
                    @Override
                    public void visitYield(JCYield tree) {
                        if (tree.target == speculativeTree)
                            buf.add(tree);
                        super.visitYield(tree);
                    }
                }.scan(speculativeTree.cases);
                res = buf.toList();
                yieldExpressions = Optional.of(res);
                return res;
            });
        }

        @Override
        ArgumentType<JCSwitchExpression> dup(JCSwitchExpression tree, Env<AttrContext> env) {
            return new SwitchExpressionType(tree, env, speculativeTree, speculativeTypes);
        }
    }

    
Argument type for explicit lambdas.
/**
     * Argument type for explicit lambdas.
     */
    class ExplicitLambdaType extends ArgumentType<JCLambda> {

        
List of argument types (lazily populated). /** List of argument types (lazily populated). */
        Optional<List<Type>> argtypes = Optional.empty();

        
List of return expressions (lazily populated). /** List of return expressions (lazily populated). */
        Optional<List<JCReturn>> returnExpressions = Optional.empty();

        ExplicitLambdaType(JCLambda originalLambda, Env<AttrContext> env, JCLambda speculativeLambda) {
            this(originalLambda, env, speculativeLambda, new HashMap<>());
        }

        ExplicitLambdaType(JCLambda originalLambda, Env<AttrContext> env, JCLambda speculativeLambda, Map<ResultInfo, Type> speculativeTypes) {
            super(originalLambda, env, speculativeLambda, speculativeTypes);
        }

        
Compute argument types (if needed). /** Compute argument types (if needed). */
        List<Type> argtypes() {
            return argtypes.orElseGet(() -> {
                List<Type> res = TreeInfo.types(speculativeTree.params);
                argtypes = Optional.of(res);
                return res;
            });
        }

        
Compute return expressions (if needed). /** Compute return expressions (if needed). */
        List<JCReturn> returnExpressions() {
            return returnExpressions.orElseGet(() -> {
                final List<JCReturn> res;
                ListBuffer<JCReturn> buf = new ListBuffer<>();
                new LambdaReturnScanner() {
                    @Override
                    public void visitReturn(JCReturn tree) {
                        buf.add(tree);
                    }
                }.scan(speculativeTree.body);
                res = buf.toList();
                returnExpressions = Optional.of(res);
                return res;
            });
        }

        @Override
        Type overloadCheck(ResultInfo resultInfo, DeferredAttrContext deferredAttrContext) {
            try {
                //compute target-type; this logic could be shared with Attr
                TargetInfo targetInfo = attr.getTargetInfo(speculativeTree, resultInfo, argtypes());
                Type lambdaType = targetInfo.descriptor;
                Type currentTarget = targetInfo.target;
                //check compatibility
                checkLambdaCompatible(lambdaType, resultInfo);
                return currentTarget;
            } catch (FunctionDescriptorLookupError ex) {
                resultInfo.checkContext.report(null, ex.getDiagnostic());
                return null; //cannot get here
            }
        }

        
Check lambda against given target result /** Check lambda against given target result */
        private void checkLambdaCompatible(Type descriptor, ResultInfo resultInfo) {
            CheckContext checkContext = resultInfo.checkContext;
            ResultInfo bodyResultInfo = attr.lambdaBodyResult(speculativeTree, descriptor, resultInfo);
            switch (speculativeTree.getBodyKind()) {
                case EXPRESSION:
                    checkSpeculative(speculativeTree.body, speculativeTree.body.type, bodyResultInfo);
                    break;
                case STATEMENT:
                    for (JCReturn ret : returnExpressions()) {
                        checkReturnInStatementLambda(ret, bodyResultInfo);
                    }
                    break;
            }

            attr.checkLambdaCompatible(speculativeTree, descriptor, checkContext);
        }

        
This is an inlined version of Attr.visitReturn(JCReturn). /**
         * This is an inlined version of {@link Attr#visitReturn(JCReturn)}.
         */
        void checkReturnInStatementLambda(JCReturn ret, ResultInfo resultInfo) {
            if (resultInfo.pt.hasTag(VOID) && ret.expr != null) {
                //fail - if the function type's result is void, the lambda body must be a void-compatible block.
                resultInfo.checkContext.report(speculativeTree.pos(),
                        diags.fragment("unexpected.ret.val"));
            } else if (!resultInfo.pt.hasTag(VOID)) {
                if (ret.expr == null) {
                    //fail - if the function type's result is non-void, the lambda body must be a value-compatible block.
                    resultInfo.checkContext.report(speculativeTree.pos(),
                            diags.fragment("missing.ret.val"));
                }
                checkSpeculative(ret.expr, ret.expr.type, resultInfo);
            }
        }

        
Get the type associated with given return expression. /** Get the type associated with given return expression. */
        Type getReturnType(JCReturn ret) {
            if (ret.expr == null) {
                return syms.voidType;
            } else {
                return ret.expr.type;
            }
        }

        @Override
        ArgumentType<JCLambda> dup(JCLambda tree, Env<AttrContext> env) {
            return new ExplicitLambdaType(tree, env, speculativeTree, speculativeTypes);
        }
    }

    
Argument type for methods/constructors.
/**
     * Argument type for methods/constructors.
     */
    abstract class ResolvedMemberType<E extends JCExpression> extends ArgumentType<E> {

        public ResolvedMemberType(JCExpression tree, Env<AttrContext> env, E speculativeMethod, Map<ResultInfo, Type> speculativeTypes) {
            super(tree, env, speculativeMethod, speculativeTypes);
        }

        @Override
        Type overloadCheck(ResultInfo resultInfo, DeferredAttrContext deferredAttrContext) {
            Type mtype = methodType();
            ResultInfo localInfo = resultInfo(resultInfo);
            Type t;
            if (mtype != null && mtype.hasTag(METHOD) && mtype.isPartial()) {
                //poly invocation
                t = ((PartiallyInferredMethodType)mtype).check(localInfo);
            } else {
                //standalone invocation
                t = localInfo.check(tree.pos(), speculativeTree.type);
            }
            speculativeTypes.put(localInfo, t);
            return t;
        }

        
Get the result info to be used for performing an overload check.
/**
         * Get the result info to be used for performing an overload check.
         */
        abstract ResultInfo resultInfo(ResultInfo resultInfo);

        
Get the method type to be used for performing an overload check.
/**
         * Get the method type to be used for performing an overload check.
         */
        abstract Type methodType();
    }

    
Argument type for methods.
/**
     * Argument type for methods.
     */
    class ResolvedMethodType extends ResolvedMemberType<JCMethodInvocation> {

        public ResolvedMethodType(JCExpression tree, Env<AttrContext> env, JCMethodInvocation speculativeTree) {
            this(tree, env, speculativeTree, new HashMap<>());
        }

        public ResolvedMethodType(JCExpression tree, Env<AttrContext> env, JCMethodInvocation speculativeTree, Map<ResultInfo, Type> speculativeTypes) {
            super(tree, env, speculativeTree, speculativeTypes);
        }

        @Override
        ResultInfo resultInfo(ResultInfo resultInfo) {
            return resultInfo;
        }

        @Override
        Type methodType() {
            return speculativeTree.meth.type;
        }

        @Override
        ArgumentType<JCMethodInvocation> dup(JCMethodInvocation tree, Env<AttrContext> env) {
            return new ResolvedMethodType(tree, env, speculativeTree, speculativeTypes);
        }
    }

    
Argument type for constructors.
/**
     * Argument type for constructors.
     */
    class ResolvedConstructorType extends ResolvedMemberType<JCNewClass> {

        public ResolvedConstructorType(JCExpression tree, Env<AttrContext> env, JCNewClass speculativeTree) {
            this(tree, env, speculativeTree, new HashMap<>());
        }

        public ResolvedConstructorType(JCExpression tree, Env<AttrContext> env, JCNewClass speculativeTree, Map<ResultInfo, Type> speculativeTypes) {
            super(tree, env, speculativeTree, speculativeTypes);
        }

        @Override
        ResultInfo resultInfo(ResultInfo resultInfo) {
            return resultInfo.dup(attr.diamondContext(speculativeTree, speculativeTree.clazz.type.tsym, resultInfo.checkContext));
        }

        @Override
        Type methodType() {
            return (speculativeTree.constructorType != null) ?
                    speculativeTree.constructorType.baseType() : syms.errType;
        }

        @Override
        ArgumentType<JCNewClass> dup(JCNewClass tree, Env<AttrContext> env) {
            return new ResolvedConstructorType(tree, env, speculativeTree, speculativeTypes);
        }
    }

    
An instance of this class represents a unique position in a compilation unit. A unique
position is made up of (i) a unique position in a source file (char offset) and (ii)
a source file info.
/**
     * An instance of this class represents a unique position in a compilation unit. A unique
     * position is made up of (i) a unique position in a source file (char offset) and (ii)
     * a source file info.
     */
    class UniquePos {

        
Char offset. /** Char offset. */
        int pos;

        
Source info. /** Source info. */
        DiagnosticSource source;

        UniquePos(JCTree tree) {
            this.pos = tree.pos;
            this.source = log.currentSource();
        }

        @Override
        public int hashCode() {
            return pos << 16 + source.hashCode();
        }

        @Override
        public boolean equals(Object obj) {
            if (obj instanceof UniquePos) {
                UniquePos that = (UniquePos)obj;
                return pos == that.pos && source == that.source;
            } else {
                return false;
            }
        }

        @Override
        public String toString() {
            return source.getFile().getName() + " @ " + source.getLineNumber(pos);
        }
    }
}