/*
* Copyright 2009 The Closure Compiler Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.javascript.jscomp;
import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableSet;
import com.google.javascript.jscomp.CodingConvention.SubclassRelationship;
import com.google.javascript.jscomp.NodeTraversal.Callback;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import java.util.ArrayList;
import java.util.List;
/**
* Callback that gathers subexpressions that may have side effects
* and appends copies of those subexpressions to the replacements
* list. In the case of branching subexpressions, it simplifies the
* subexpression before adding it to the replacement list.
*
*/
class GatherSideEffectSubexpressionsCallback implements Callback {
/**
* Used by GatherSideEffectSubexpressionsCallback to notify client
* code about side effect expressions that should be kept.
*/
interface SideEffectAccumulator {
/**
* Returns true if the "mixin" and "inherits" function calls
* should be treated as if they had side effects.
*/
boolean classDefiningCallsHaveSideEffects();
/**
* Adds subtree to the list of nodes that have side effects.
*
* @param original - root of the tree.
*/
void keepSubTree(Node original);
/**
* Simplifies a subtree whose root node is an AND or OR expression
* and adds the resulting subtree to the list of nodes that have
* side effects.
*
* @param original - root of the and/or expression.
*/
void keepSimplifiedShortCircuitExpression(Node original);
/**
* Simplifies a subtree whose root node is a HOOK expression
* and adds the resulting subtree to the list of nodes that have
* side effects.
*
* @param hook - root of the hook expression.
* @param thenHasSideEffects - then branch has side effects
* @param elseHasSideEffects - else branch has side effects
*/
void keepSimplifiedHookExpression(Node hook,
boolean thenHasSideEffects,
boolean elseHasSideEffects);
}
/**
* Populates the provided replacement list by appending copies of
* subtrees that have side effects.
*
* It is OK if this class tears up the original tree, because
* we're going to throw the tree out anyway.
*/
static final class GetReplacementSideEffectSubexpressions
implements SideEffectAccumulator {
private final AbstractCompiler compiler;
private final List<Node> replacements;
/**
* Creates the accumulator.
*
* @param compiler - the AbstractCompiler
* @param replacements - list to accumulate into
*/
GetReplacementSideEffectSubexpressions(AbstractCompiler compiler,
List<Node> replacements) {
this.compiler = compiler;
this.replacements = replacements;
}
@Override
public boolean classDefiningCallsHaveSideEffects() {
return true;
}
@Override
public void keepSubTree(Node original) {
if (original.getParent() != null) {
original.detach();
}
replacements.add(original);
}
@Override
public void keepSimplifiedShortCircuitExpression(Node original) {
Preconditions.checkArgument(
(original.isAnd()) || (original.isOr()),
"Expected: AND or OR, Got: %s",
original.getToken());
Node left = original.getFirstChild();
Node right = left.getNext();
Node simplifiedRight = simplifyShortCircuitBranch(right);
original.detachChildren();
original.addChildToBack(left);
original.addChildToBack(simplifiedRight);
keepSubTree(original);
}
@Override
public void keepSimplifiedHookExpression(Node hook,
boolean thenHasSideEffects,
boolean elseHasSideEffects) {
Preconditions.checkArgument(hook.isHook(), "Expected: HOOK, Got: %s", hook.getToken());
Node condition = hook.getFirstChild();
Node thenBranch = condition.getNext();
Node elseBranch = thenBranch.getNext();
if (thenHasSideEffects && elseHasSideEffects) {
hook.detachChildren();
hook.addChildToBack(condition);
hook.addChildToBack(simplifyShortCircuitBranch(thenBranch));
hook.addChildToBack(simplifyShortCircuitBranch(elseBranch));
keepSubTree(hook);
} else if (thenHasSideEffects || elseHasSideEffects) {
Token type = thenHasSideEffects ? Token.AND : Token.OR;
Node body = thenHasSideEffects ? thenBranch : elseBranch;
Node simplified = new Node(
type, condition.detach(),
simplifyShortCircuitBranch(body))
.useSourceInfoIfMissingFrom(hook);
keepSubTree(simplified);
} else {
throw new IllegalArgumentException(
"keepSimplifiedHookExpression must keep at least 1 branch");
}
}
private Node simplifyShortCircuitBranch(Node node) {
List<Node> parts = new ArrayList<>();
NodeTraversal.traverseEs6(
compiler, node,
new GatherSideEffectSubexpressionsCallback(
compiler,
new GetReplacementSideEffectSubexpressions(compiler, parts)));
Node ret = null;
for (Node part : parts) {
if (ret != null) {
ret = IR.comma(ret, part).srcref(node);
} else {
ret = part;
}
}
if (ret == null) {
throw new IllegalArgumentException(
"expected at least one side effect subexpression in short "
+ "circuit branch.");
}
return ret;
}
}
private static final ImmutableSet<Token> FORBIDDEN_TYPES =
ImmutableSet.of(Token.BLOCK, Token.SCRIPT, Token.VAR, Token.EXPR_RESULT, Token.RETURN);
private final AbstractCompiler compiler;
private final SideEffectAccumulator accumulator;
/**
* @param compiler - AbstractCompiler object
* @param accumulator - object that will accumulate roots of
* subtrees that have side effects.
*/
GatherSideEffectSubexpressionsCallback(AbstractCompiler compiler,
SideEffectAccumulator accumulator) {
this.compiler = compiler;
this.accumulator = accumulator;
}
/**
* Determines if a call defines a class inheritance or mixing
* relation, according to the current coding convention.
*/
private boolean isClassDefiningCall(Node callNode) {
SubclassRelationship classes =
compiler.getCodingConvention().getClassesDefinedByCall(callNode);
return classes != null;
}
/**
* Computes the list of subtrees whose root nodes have side effects.
*
* <p>If the current subtree's root has side effects this method should
* call accumulator.keepSubTree and return 'false' to add the
* subtree to the result list and avoid avoid traversing the nodes children.
*
* <p>Branching nodes whose then or else branch contain side effects
* must be simplified by doing a recursive traversal; this method
* should call the appropriate accumulator 'keepSimplified' method
* and return 'false' to stop the regular traversal.
*/
@Override
public boolean shouldTraverse(
NodeTraversal traversal, Node node, Node parent) {
if (FORBIDDEN_TYPES.contains(node.getToken()) || NodeUtil.isControlStructure(node)) {
throw new IllegalArgumentException(node.getToken() + " nodes are not supported.");
}
// Do not recurse into nested functions.
if (node.isFunction()) {
return false;
}
// simplify and maybe keep hook expression.
if (node.isHook()) {
return processHook(node);
}
// simplify and maybe keep AND/OR expression.
if ((node.isAnd()) || (node.isOr())) {
return processShortCircuitExpression(node);
}
if (!NodeUtil.nodeTypeMayHaveSideEffects(node, compiler)) {
return true;
} else {
// Node type suggests that the expression has side effects.
if (node.isCall()) {
return processFunctionCall(node);
} else if (node.isNew()) {
return processConstructorCall(node);
} else {
accumulator.keepSubTree(node);
return false;
}
}
}
/**
* Processes an AND or OR expression.
*
* @return true to continue traversal, false otherwise
*/
boolean processShortCircuitExpression(Node node) {
Preconditions.checkArgument(
(node.isAnd()) || (node.isOr()), "Expected: AND or OR, Got: %s", node.getToken());
// keep whole expression if RHS of the branching expression
// contains a call.
Node left = node.getFirstChild();
Node right = left.getNext();
if (NodeUtil.mayHaveSideEffects(right, compiler)) {
accumulator.keepSimplifiedShortCircuitExpression(node);
return false;
} else {
return true;
}
}
/**
* Processes a HOOK expression.
*
* @return true to continue traversal, false otherwise
*/
boolean processHook(Node node) {
Preconditions.checkArgument(node.isHook(), "Expected: HOOK, Got: %s", node.getToken());
Node condition = node.getFirstChild();
Node ifBranch = condition.getNext();
Node elseBranch = ifBranch.getNext();
boolean thenHasSideEffects = NodeUtil.mayHaveSideEffects(
ifBranch, compiler);
boolean elseHasSideEffects = NodeUtil.mayHaveSideEffects(
elseBranch, compiler);
if (thenHasSideEffects || elseHasSideEffects) {
accumulator.keepSimplifiedHookExpression(
node, thenHasSideEffects, elseHasSideEffects);
return false;
} else {
return true;
}
}
/**
* Processes a CALL expression.
*
* @return true to continue traversal, false otherwise
*/
boolean processFunctionCall(Node node) {
Preconditions.checkArgument(node.isCall(), "Expected: CALL, Got: %s", node.getToken());
// Calls to functions that are known to be "pure" have no side
// effects.
Node functionName = node.getFirstChild();
if (functionName.isName() || functionName.isGetProp()) {
if (!accumulator.classDefiningCallsHaveSideEffects() &&
isClassDefiningCall(node)) {
return true;
}
}
if (!NodeUtil.functionCallHasSideEffects(node)) {
return true;
}
accumulator.keepSubTree(node);
return false;
}
/**
* Processes a NEW expression.
*
* @return true to continue traversal, false otherwise
*/
boolean processConstructorCall(Node node) {
Preconditions.checkArgument(node.isNew(), "Expected: NEW, Got: %s", node.getToken());
// Calls to constructors that are known to be "pure" have no
// side effects.
if (!NodeUtil.constructorCallHasSideEffects(node)) {
return true;
}
accumulator.keepSubTree(node);
return false;
}
@Override
public void visit(NodeTraversal traversal, Node node, Node parent) {}
}