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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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.
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 * 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).
 *
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package com.sun.tools.javac.comp;

import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.tree.JCTree;
import com.sun.tools.javac.tree.JCTree.JCFieldAccess;
import com.sun.tools.javac.tree.JCTree.JCIdent;
import com.sun.tools.javac.tree.JCTree.JCLiteral;
import com.sun.tools.javac.tree.JCTree.JCVariableDecl;
import com.sun.tools.javac.tree.TreeInfo;
import com.sun.tools.javac.tree.TreeScanner;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;

A tree visitor that computes a hash code.
/** A tree visitor that computes a hash code. */
public class TreeHasher extends TreeScanner { private final Map<Symbol, Integer> symbolHashes; private int result = 17; public TreeHasher(Map<Symbol, Integer> symbolHashes) { this.symbolHashes = Objects.requireNonNull(symbolHashes); } public static int hash(JCTree tree, Collection<? extends Symbol> symbols) { if (tree == null) { return 0; } Map<Symbol, Integer> symbolHashes = new HashMap<>(); symbols.forEach(s -> symbolHashes.put(s, symbolHashes.size())); TreeHasher hasher = new TreeHasher(symbolHashes); tree.accept(hasher); return hasher.result; } private void hash(Object object) { result = 31 * result + Objects.hashCode(object); } @Override public void scan(JCTree tree) { if (tree == null) { return; } tree = TreeInfo.skipParens(tree); if (tree.type != null) { Object value = tree.type.constValue(); if (value != null) { hash(value); return; } } hash(tree.getTag()); tree.accept(this); } @Override public void visitLiteral(JCLiteral tree) { hash(tree.value); super.visitLiteral(tree); } @Override public void visitIdent(JCIdent tree) { Symbol sym = tree.sym; if (sym != null) { Integer hash = symbolHashes.get(sym); if (hash != null) { hash(hash); return; } } hash(sym); } @Override public void visitSelect(JCFieldAccess tree) { hash(tree.sym); super.visitSelect(tree); } @Override public void visitVarDef(JCVariableDecl tree) { symbolHashes.computeIfAbsent(tree.sym, k -> symbolHashes.size()); super.visitVarDef(tree); } }