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/*
* 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 static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static java.util.stream.Collectors.toList;
import com.google.common.base.MoreObjects;
import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Multimap;
import com.google.common.collect.Multimaps;
import com.google.common.collect.SetMultimap;
import com.google.errorprone.annotations.DoNotCall;
import com.google.javascript.jscomp.CodingConvention.Cache;
import com.google.javascript.jscomp.NodeTraversal.Callback;
import com.google.javascript.jscomp.NodeTraversal.ScopedCallback;
import com.google.javascript.jscomp.OptimizeCalls.ReferenceMap;
import com.google.javascript.jscomp.graph.DiGraph;
import com.google.javascript.jscomp.graph.DiGraph.DiGraphNode;
import com.google.javascript.jscomp.graph.FixedPointGraphTraversal;
import com.google.javascript.jscomp.graph.LinkedDirectedGraph;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.jstype.FunctionType;
import com.google.javascript.rhino.jstype.JSType;
import com.google.javascript.rhino.jstype.JSTypeNative;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.function.Predicate;
import javax.annotation.Nullable;
/**
* Compiler pass that computes function purity and annotates invocation nodes with those purities.
*
* A function is pure if it has no outside visible side effects, and the result of the
* computation does not depend on external factors that are beyond the control of the application;
* repeated calls to the function should return the same value as long as global state hasn't
* changed.
*
*
`Date.now` is an example of a function that has no side effects but is not pure.
*
*
Functions are not tracked individually but rather in aggregate by their name. This is because
* it's impossible to determine exactly which function named "foo" is being called at a particular
* site. Therefore, if any function "foo" has a particular side-effect, all
* invocations "foo" are assumed to trigger it.
*
*
This pass could be greatly improved by proper tracking of locals within function bodies. Every
* instance of the call to {@link NodeUtil#evaluatesToLocalValue(Node)} and {@link
* NodeUtil#allArgsUnescapedLocal(Node)} do not actually take into account local variables. They
* only assume literals, primitives, and operations on primitives are local.
*
* @author [email protected] (John Lenz)
* @author [email protected] (Thomas Deegan)
*/
class PureFunctionIdentifier implements OptimizeCalls.CallGraphCompilerPass {
// A prefix to differentiate property names from variable names.
// TODO(nickreid): This pass could be made more efficient if props and variables were maintained
// in separate datastructures. We wouldn't allocate a bunch of extra strings.
private static final String PROP_NAME_PREFIX = ".";
private final AbstractCompiler compiler;
private final AstAnalyzer astAnalyzer;
/**
* Map of function names to the summary of the functions with that name.
*
*
Variable names are recorded as-is. Property names are prefixed with {@link
* #PROP_NAME_PREFIX} to differentiate them from variable names.
*
* @see {@link AmbiguatedFunctionSummary}
*/
private final Map summariesByName = new HashMap<>();
/**
* Mapping from function node to summaries for all names associated with that node.
*
* This is a multimap because you can construct situations in which a function node has
* multiple names, and therefore multiple associated summaries. For example:
*
*
* // Not enough type information to collapse/disambiguate properties on "staticMethod".
* SomeClass.staticMethod = function anotherName() {};
* OtherClass.staticMethod = function() { global++; }
*
*
* In this situation we want to keep the side effects for "staticMethod" which are "global"
* separate from "anotherName". Hence the function node should point to the {@link
* AmbiguatedFunctionSummary} for both "staticMethod" and "anotherName".
*
*
We could instead store a map of FUNCTION nodes to names, and then join that with the name of
* names to infos. However, since names are 1:1 with infos, it's more effecient to "pre-join" in
* this way.
*/
private final Multimap summariesForAllNamesOfFunctionByNode =
ArrayListMultimap.create();
// List of all function call sites. Storing them here during the function analysis traversal
// prevents us from doing a second traversal to annotate them with side-effects. We can just
// iterate the list.
private final List allFunctionCalls = new ArrayList<>();
/**
* A graph linking the summary of a function callee to the summaries of its callers.
*
* Each node represents an aggregate summary of every function with a particular name. The edge
* values indicate the details of the invocation necessary to propagate function impurity from
* callee to caller.
*
*
Once all the invocation edges are in place, this graph will be traversed to transitively
* propagate side-effect information across it's entire structure. The resultant side-effects can
* then be attached to invocation sites.
*/
private final LinkedDirectedGraph
reverseCallGraph = LinkedDirectedGraph.createWithoutAnnotations();
/**
* A summary for a function for which no definition was found.
*
* We assume it has all possible side-effects. It's useful for references like function
* parameters, or inner functions.
*/
private final AmbiguatedFunctionSummary unknownFunctionSummary =
AmbiguatedFunctionSummary.createInGraph(reverseCallGraph, "").setAllFlags();
private boolean hasProcessed = false;
public PureFunctionIdentifier(AbstractCompiler compiler) {
this.compiler = checkNotNull(compiler);
this.astAnalyzer = compiler.getAstAnalyzer();
}
@Override
public void process(Node externs, Node root, ReferenceMap references) {
checkState(compiler.getLifeCycleStage().isNormalized());
checkState(
!hasProcessed, "PureFunctionIdentifier::process may only be called once per instance.");
this.hasProcessed = true;
populateDatastructuresForAnalysisTraversal(references);
NodeTraversal.traverse(compiler, externs, new ExternFunctionAnnotationAnalyzer());
NodeTraversal.traverse(compiler, root, new FunctionBodyAnalyzer());
propagateSideEffects();
markPureFunctionCalls();
}
/**
* Traverses an {@code expr} to collect nodes representing potential callables that it may resolve
* to well known callables.
*
* @see {@link #collectCallableLeavesInternal}
* @return the disovered callables, or {@code null} if an unexpected possible value was found.
*/
@Nullable
private static ImmutableList collectCallableLeaves(Node expr) {
ArrayList callables = new ArrayList<>();
boolean allLegal = collectCallableLeavesInternal(expr, callables);
return allLegal ? ImmutableList.copyOf(callables) : null;
}
/**
* Traverses an {@code expr} to collect nodes representing potential callables that it may resolve
* to well known callables.
*
* For example:
*
*
* `a.c || b` => [a.c, b]
* `x ? a.c : b` => [a.c, b]
* `(function f() { }) && x || class Foo { constructor() { } }` => [function, x, constructor]`
*
*
* This function is applicable to finding both assignment aliases and call targets. That is,
* one way to find the possible callees of an invocation is to pass the complex expression
* representing the final callee to this method.
*
*
This function uses a white-list approach. If a node that isn't understood is detected, the
* entire collection is invalidated.
*
* @see {@link #collectCallableLeaves}
* @param exp A possibly complicated expression.
* @param results The collection of qualified names and functions.
* @return {@code true} iff only understood results were discovered.
*/
private static boolean collectCallableLeavesInternal(Node expr, ArrayList results) {
switch (expr.getToken()) {
case FUNCTION:
case GETPROP:
case NAME:
results.add(expr);
return true;
case SUPER:
{
// Pretend that `super` is an alias for the superclass reference.
Node clazz = checkNotNull(NodeUtil.getEnclosingClass(expr));
Node function = checkNotNull(NodeUtil.getEnclosingFunction(expr));
Node ctorDef = checkNotNull(NodeUtil.getEs6ClassConstructorMemberFunctionDef(clazz));
// The only place SUPER should be a callable expression is in a class ctor.
checkState(
function.isFirstChildOf(ctorDef), "Unknown SUPER reference: %s", expr.toStringTree());
return collectCallableLeavesInternal(clazz.getSecondChild(), results);
}
case CLASS:
{
// Collect the constructor function, or failing that, the superclass reference.
@Nullable Node ctorDef = NodeUtil.getEs6ClassConstructorMemberFunctionDef(expr);
if (ctorDef != null) {
return collectCallableLeavesInternal(ctorDef.getOnlyChild(), results);
} else if (expr.getSecondChild().isEmpty()) {
return true; // A class an implicit ctor is pure when there is no superclass.
} else {
return collectCallableLeavesInternal(expr.getSecondChild(), results);
}
}
case AND:
case OR:
return collectCallableLeavesInternal(expr.getFirstChild(), results)
&& collectCallableLeavesInternal(expr.getSecondChild(), results);
case COMMA:
case ASSIGN:
return collectCallableLeavesInternal(expr.getSecondChild(), results);
case HOOK:
return collectCallableLeavesInternal(expr.getChildAtIndex(1), results)
&& collectCallableLeavesInternal(expr.getChildAtIndex(2), results);
case NEW_TARGET:
case THIS:
// These could be an alias to any function. Treat them as an unknown callable.
default:
return false; // Unsupported call type.
}
}
/**
* Return {@code true} only if {@code rvalue} is defintely a reference reading a value.
*
* For the most part it's sufficient to cover cases where a nominal function reference might
* reasonably be expected, since those are the values that matter to analysis.
*
*
It's very important that this never returns {@code true} for an L-value, including when new
* syntax is added to the language. That would cause some impure functions to be considered pure.
* Therefore, this method is a very explict whitelist. Anything that's unrecognized is considered
* not an R-value. This is insurance against new syntax.
*
*
New cases can be added as needed to increase the accuracy of the analysis. They just have to
* be verified as always R-values.
*/
private static boolean isDefinitelyRValue(Node rvalue) {
Node parent = rvalue.getParent();
switch (parent.getToken()) {
case AND:
case COMMA:
case HOOK:
case OR:
// Function values pass through conditionals.
case EQ:
case NOT:
case SHEQ:
// Functions can be usefully compared for equality / existence.
case ARRAYLIT:
case CALL:
case NEW:
case TAGGED_TEMPLATELIT:
// Functions are the callees and parameters of an invocation.
case INSTANCEOF:
case TYPEOF:
// Often used to determine if a ctor/method exists/matches.
case GETELEM:
case GETPROP:
// Many functions, especially ctors, have properties.
case RETURN:
case YIELD:
// Higher order functions return functions.
return true;
case SWITCH:
case CASE:
// Delegating on the identity of a function.
case IF:
case WHILE:
// Checking the existence of an optional function.
return rvalue.isFirstChildOf(parent);
case EXPR_RESULT:
// Extern declarations are sometimes stubs. These must be considered L-values with no
// associated R-values.
return !rvalue.isFromExterns();
case CLASS: // `extends` clause.
case ASSIGN:
return rvalue.isSecondChildOf(parent);
case STRING_KEY: // Assignment to an object literal property. Excludes object destructuring.
return parent.getParent().isObjectLit();
default:
// Anything not explicitly listed may not be an R-value. We only worry about the likely
// cases for nominal function values since those are what interest us and its safe to miss
// some R-values. It's more important that we correctly identify L-values.
return false;
}
}
private ImmutableList getGoogCacheCallableExpression(Cache cacheCall) {
checkNotNull(cacheCall);
ImmutableList.Builder builder =
ImmutableList.builder().addAll(collectCallableLeaves(cacheCall.valueFn));
if (cacheCall.keyFn != null) {
builder.addAll(collectCallableLeaves(cacheCall.keyFn));
}
return builder.build();
}
private List getSummariesForCallee(Node invocation) {
checkArgument(NodeUtil.isInvocation(invocation), invocation);
Cache cacheCall = compiler.getCodingConvention().describeCachingCall(invocation);
final ImmutableList callees;
if (cacheCall != null) {
callees = getGoogCacheCallableExpression(cacheCall);
} else if (isInvocationViaCallOrApply(invocation)) {
callees = ImmutableList.of(invocation.getFirstFirstChild());
} else {
callees = collectCallableLeaves(invocation.getFirstChild());
}
if (callees == null) {
return ImmutableList.of(unknownFunctionSummary);
}
List results = new ArrayList<>();
for (Node callee : callees) {
if (callee.isFunction()) {
checkState(callee.isFunction(), callee);
Collection summariesForFunction =
summariesForAllNamesOfFunctionByNode.get(callee);
checkState(!summariesForFunction.isEmpty(), "Function missed during analysis: %s", callee);
results.addAll(summariesForFunction);
} else {
String calleeName = nameForReference(callee);
results.add(summariesByName.getOrDefault(calleeName, unknownFunctionSummary));
}
}
return results;
}
/**
* Fill all of the auxiliary data-structures used by this pass based on the results in {@code
* referenceMap}.
*
* This is the first step of analysis. These structures will be used by a traversal that
* analyzes the bodies of located functions for side-effects. That traversal is separate because
* it needs access to scopes and also depends on global knowledge of functions.
*/
private void populateDatastructuresForAnalysisTraversal(ReferenceMap referenceMap) {
// Merge the prop and name references into a single multimap since only the name matters.
ArrayListMultimap referencesByName = ArrayListMultimap.create();
for (Map.Entry> entry : referenceMap.getNameReferences()) {
referencesByName.putAll(entry.getKey(), entry.getValue());
}
for (Map.Entry> entry : referenceMap.getPropReferences()) {
referencesByName.putAll(PROP_NAME_PREFIX + entry.getKey(), entry.getValue());
}
// Empty function names cause a crash during analysis that is better to detect here.
// Additionally, functions require a name to be invoked in a statically analyzable way; there's
// no value in tracking the set of anonymous functions.
checkState(!referencesByName.containsKey(""));
checkState(!referencesByName.containsKey(PROP_NAME_PREFIX));
// Create and store a summary for all known names.
for (String name : referencesByName.keySet()) {
summariesByName.put(name, AmbiguatedFunctionSummary.createInGraph(reverseCallGraph, name));
}
Multimaps.asMap(referencesByName).forEach(this::populateFunctionDefinitions);
}
/**
* For a name and its set of references, record the set of functions that may define that name or
* blacklist the name if there are unclear definitions.
*
* @param name A variable or property name,
* @param references The set of all nodes representing R- and L-value references to {@code name}.
*/
private void populateFunctionDefinitions(String name, List references) {
AmbiguatedFunctionSummary summaryForName = checkNotNull(summariesByName.get(name));
// Make sure we get absolutely every R-value assigned to `name` or at the very least detect
// there are some we're missing. Overlooking a single R-value would invalidate the analysis.
List> rvaluesAssignedToName =
references.stream()
// Eliminate any references that we're sure are R-values themselves. Otherwise
// there's a high probability we'll inspect an R-value for futher R-values. We wouldn't
// find any, and then we'd have to consider `name` impure.
.filter((n) -> !isDefinitelyRValue(n))
// For anything that might be an L-reference, get the expression being assigned to it.
.map(NodeUtil::getRValueOfLValue)
// If the assigned R-value is an analyzable expression, collect all the possible
// FUNCTIONs that could result from that expression. If the expression isn't analyzable,
// represent that with `null` so we can blacklist `name`.
.map((n) -> (n == null) ? null : collectCallableLeaves(n))
.collect(toList());
if (rvaluesAssignedToName.isEmpty() || rvaluesAssignedToName.contains(null)) {
// Any of:
// - There are no L-values with this name.
// - There's a an L-value and we can't find the associated R-values.
// - There's a an L-value with R-values are not all known to be callable.
summaryForName.setAllFlags();
} else {
rvaluesAssignedToName.stream()
.flatMap(List::stream)
.forEach(
(rvalue) -> {
if (rvalue.isFunction()) {
summariesForAllNamesOfFunctionByNode.put(rvalue, summaryForName);
} else {
String rvalueName = nameForReference(rvalue);
AmbiguatedFunctionSummary rvalueSummary =
summariesByName.getOrDefault(rvalueName, unknownFunctionSummary);
reverseCallGraph.connect(
rvalueSummary.graphNode,
SideEffectPropagation.forAlias(),
summaryForName.graphNode);
}
});
}
}
/**
* Propagate side effect information in {@link #reverseCallGraph} from callees to callers.
*
* This is an iterative process executed until a fixed point, where no caller summary would be
* given new side-effects from from any callee summary, is reached.
*/
private void propagateSideEffects() {
FixedPointGraphTraversal.newTraversal(
(AmbiguatedFunctionSummary source,
SideEffectPropagation edge,
AmbiguatedFunctionSummary destination) -> edge.propagate(source, destination))
.computeFixedPoint(reverseCallGraph);
}
/** Set no side effect property at pure-function call sites. */
private void markPureFunctionCalls() {
for (Node callNode : allFunctionCalls) {
List calleeSummaries = getSummariesForCallee(callNode);
// Default to side effects, non-local results
Node.SideEffectFlags flags = new Node.SideEffectFlags();
if (calleeSummaries.isEmpty()) {
flags.setAllFlags();
} else {
flags.clearAllFlags();
for (AmbiguatedFunctionSummary calleeSummary : calleeSummaries) {
checkNotNull(calleeSummary);
if (calleeSummary.mutatesGlobalState()) {
flags.setMutatesGlobalState();
}
if (calleeSummary.mutatesArguments()) {
flags.setMutatesArguments();
}
if (calleeSummary.functionThrows()) {
flags.setThrows();
}
if (isCallOrTaggedTemplateLit(callNode)) {
if (calleeSummary.mutatesThis()) {
// A summary for "f" maps to both "f()" and "f.call()" nodes.
if (isInvocationViaCallOrApply(callNode)) {
flags.setMutatesArguments(); // `this` is actually an argument.
} else {
flags.setMutatesThis();
}
}
}
if (calleeSummary.escapedReturn()) {
flags.setReturnsTainted();
}
}
}
if (callNode.getFirstChild().isSuper()) {
// All `super()` calls (i.e. from subclass constructors) implicitly mutate `this`; they
// determine its value in the caller scope. Concretely, `super()` calls must not be removed
// or reordered. Marking them this way ensures that without pinning the enclosing function.
flags.setMutatesThis();
}
// Handle special cases (Math, RegExp)
if (isCallOrTaggedTemplateLit(callNode)) {
if (!astAnalyzer.functionCallHasSideEffects(callNode)) {
flags.clearSideEffectFlags();
}
} else if (callNode.isNew()) {
// Handle known cases now (Object, Date, RegExp, etc)
if (!astAnalyzer.constructorCallHasSideEffects(callNode)) {
flags.clearSideEffectFlags();
}
}
if (callNode.getSideEffectFlags() != flags.valueOf()) {
callNode.setSideEffectFlags(flags);
compiler.reportChangeToEnclosingScope(callNode);
}
}
}
/**
* Inspects function JSDoc for side effects and applies them to the associated {@link
* AmbiguatedFunctionSummary}.
*
* This callback is only meant for use on externs.
*/
private final class ExternFunctionAnnotationAnalyzer implements Callback {
@Override
public boolean shouldTraverse(NodeTraversal traversal, Node node, Node parent) {
return true;
}
@Override
public void visit(NodeTraversal traversal, Node node, Node parent) {
if (!node.isFunction()) {
return;
}
for (AmbiguatedFunctionSummary definitionSummary :
summariesForAllNamesOfFunctionByNode.get(node)) {
updateSideEffectsForExternFunction(node, definitionSummary);
}
}
/** Update function for @nosideeffects annotations. */
private void updateSideEffectsForExternFunction(
Node externFunction, AmbiguatedFunctionSummary summary) {
checkArgument(externFunction.isFunction());
checkArgument(externFunction.isFromExterns());
JSDocInfo info = NodeUtil.getBestJSDocInfo(externFunction);
// Handle externs.
JSType typei = externFunction.getJSType();
FunctionType functionType = typei == null ? null : typei.toMaybeFunctionType();
if (functionType == null) {
// Assume extern functions return tainted values when we have no type info to say otherwise.
summary.setEscapedReturn();
} else {
JSType retType = functionType.getReturnType();
if (!isLocalValueType(retType, compiler)) {
summary.setEscapedReturn();
}
}
if (info == null) {
// We don't know anything about this function so we assume it has side effects.
summary.setMutatesGlobalState();
summary.setFunctionThrows();
} else {
if (info.modifiesThis()) {
summary.setMutatesThis();
} else if (info.hasSideEffectsArgumentsAnnotation()) {
summary.setMutatesArguments();
} else if (!info.getThrownTypes().isEmpty()) {
summary.setFunctionThrows();
} else if (info.isNoSideEffects()) {
// Do nothing.
} else {
summary.setMutatesGlobalState();
}
}
}
/**
* Return whether {@code type} is guaranteed to be a that of a "local value".
*
*
For the purposes of purity analysis we really only care whether a return value is
* immutable and identity-less; such values can't contribute to side-effects. Therefore, this
* method is implemented to check if {@code type} is that of a primitive, since primitives
* exhibit both relevant behaviours.
*/
private boolean isLocalValueType(JSType typei, AbstractCompiler compiler) {
checkNotNull(typei);
JSType nativeObj = compiler.getTypeRegistry().getNativeType(JSTypeNative.OBJECT_TYPE);
JSType subtype = typei.meetWith(nativeObj);
// If the type includes anything related to a object type, don't assume
// anything about the locality of the value.
return subtype.isEmptyType();
}
}
private static final Predicate RHS_IS_ALWAYS_LOCAL = lhs -> true;
private static final Predicate RHS_IS_NEVER_LOCAL = lhs -> false;
private static final Predicate FIND_RHS_AND_CHECK_FOR_LOCAL_VALUE = lhs -> {
Node rhs = NodeUtil.getRValueOfLValue(lhs);
return rhs == null || NodeUtil.evaluatesToLocalValue(rhs);
};
/**
* Inspects function bodies for side effects and applies them to the associated {@link
* AmbiguatedFunctionSummary}.
*
* This callback also fills {@link #allFunctionCalls}
*/
private final class FunctionBodyAnalyzer implements ScopedCallback {
private final SetMultimap blacklistedVarsByFunction = HashMultimap.create();
private final SetMultimap taintedVarsByFunction = HashMultimap.create();
@Override
public boolean shouldTraverse(NodeTraversal traversal, Node node, Node parent) {
if (!node.isFunction()) {
return true;
}
// Functions need to be processed as part of pre-traversal so that an entry for the function
// exists in the summariesForAllNamesOfFunctionByNode map when processing assignments and
// calls within the body.
if (!summariesForAllNamesOfFunctionByNode.containsKey(node)) {
// This function was not part of a definition which is why it was not created by
// {@link populateDatastructuresForAnalysisTraversal}. For example, an anonymous function.
AmbiguatedFunctionSummary summary =
AmbiguatedFunctionSummary.createInGraph(reverseCallGraph, "");
summariesForAllNamesOfFunctionByNode.put(node, summary);
}
return true;
}
@Override
public void visit(NodeTraversal traversal, Node node, Node parent) {
if (!compiler.getAstAnalyzer().nodeTypeMayHaveSideEffects(node) && !node.isReturn()) {
return;
}
if (NodeUtil.isInvocation(node)) {
// We collect these after filtering for side-effects because there's no point re-processing
// a known pure call. This analysis is run multiple times, but no optimization will make a
// pure function impure.
allFunctionCalls.add(node);
}
Scope containerScope = traversal.getScope().getClosestContainerScope();
if (!containerScope.isFunctionScope()) {
// We only need to look at nodes in function scopes.
return;
}
Node enclosingFunction = containerScope.getRootNode();
for (AmbiguatedFunctionSummary encloserSummary :
summariesForAllNamesOfFunctionByNode.get(enclosingFunction)) {
checkNotNull(encloserSummary);
updateSideEffectsForNode(encloserSummary, traversal, node, enclosingFunction);
}
}
public void updateSideEffectsForNode(
AmbiguatedFunctionSummary encloserSummary,
NodeTraversal traversal,
Node node,
Node enclosingFunction) {
switch (node.getToken()) {
case ASSIGN:
// e.g.
// lhs = rhs;
// ({x, y} = object);
visitLhsNodes(
encloserSummary,
traversal.getScope(),
enclosingFunction,
NodeUtil.findLhsNodesInNode(node),
FIND_RHS_AND_CHECK_FOR_LOCAL_VALUE);
break;
case INC: // e.g. x++;
case DEC:
case DELPROP:
visitLhsNodes(
encloserSummary,
traversal.getScope(),
enclosingFunction,
ImmutableList.of(node.getOnlyChild()),
// The value assigned by a unary op is always local.
RHS_IS_ALWAYS_LOCAL);
break;
case FOR_AWAIT_OF:
setSideEffectsForControlLoss(encloserSummary); // Control is lost while awaiting.
// Fall through.
case FOR_OF:
// e.g.
// for (const {prop1, prop2} of iterable) {...}
// for ({prop1: x.p1, prop2: x.p2} of iterable) {...}
//
// TODO(bradfordcsmith): Possibly we should try to determine whether the iteration itself
// could have side effects.
visitLhsNodes(
encloserSummary,
traversal.getScope(),
enclosingFunction,
NodeUtil.findLhsNodesInNode(node),
// The RHS of a for-of must always be an iterable, making it a container, so we can't
// consider its contents to be local
RHS_IS_NEVER_LOCAL);
checkIteratesImpureIterable(node, encloserSummary);
break;
case FOR_IN:
// e.g.
// for (prop in obj) {...}
// Also this, though not very useful or readable.
// for ([char1, char2, ...x.rest] in obj) {...}
visitLhsNodes(
encloserSummary,
traversal.getScope(),
enclosingFunction,
NodeUtil.findLhsNodesInNode(node),
// A for-in always assigns a string, which is a local value by definition.
RHS_IS_ALWAYS_LOCAL);
break;
case CALL:
case NEW:
case TAGGED_TEMPLATELIT:
visitCall(encloserSummary, node);
break;
case NAME:
// Variable definition are not side effects. Check that the name appears in the context of
// a variable declaration.
checkArgument(NodeUtil.isNameDeclaration(node.getParent()), node.getParent());
Node value = node.getFirstChild();
// Assignment to local, if the value isn't a safe local value,
// new object creation or literal or known primitive result
// value, add it to the local blacklist.
if (value != null && !NodeUtil.evaluatesToLocalValue(value)) {
Scope scope = traversal.getScope();
Var var = scope.getVar(node.getString());
blacklistedVarsByFunction.put(enclosingFunction, var);
}
break;
case THROW:
encloserSummary.setFunctionThrows();
break;
case RETURN:
if (node.hasChildren() && !NodeUtil.evaluatesToLocalValue(node.getFirstChild())) {
encloserSummary.setEscapedReturn();
}
break;
case YIELD:
checkIteratesImpureIterable(node, encloserSummary); // `yield*` triggers iteration.
// 'yield' throws if the caller calls `.throw` on the generator object.
setSideEffectsForControlLoss(encloserSummary);
break;
case AWAIT:
// 'await' throws if the promise it's waiting on is rejected.
setSideEffectsForControlLoss(encloserSummary);
break;
case REST:
case SPREAD:
checkIteratesImpureIterable(node, encloserSummary);
break;
default:
if (NodeUtil.isCompoundAssignmentOp(node)) {
// e.g.
// x += 3;
visitLhsNodes(
encloserSummary,
traversal.getScope(),
enclosingFunction,
ImmutableList.of(node.getFirstChild()),
// The update assignments (e.g. `+=) always assign primitive, and therefore local,
// values.
RHS_IS_ALWAYS_LOCAL);
break;
}
throw new IllegalArgumentException("Unhandled side effect node type " + node);
}
}
/**
* Inspect {@code node} for impure iteration and assign the appropriate side-effects to {@code
* encloserSummary} if so.
*/
private void checkIteratesImpureIterable(Node node, AmbiguatedFunctionSummary encloserSummary) {
if (!NodeUtil.iteratesImpureIterable(node)) {
return;
}
// Treat the (possibly implicit) call to `iterator.next()` as having the same effects as any
// other unknown function call.
encloserSummary.setFunctionThrows();
encloserSummary.setMutatesGlobalState();
// The iterable may be stateful and a param.
encloserSummary.setMutatesArguments();
}
/**
* Assigns the set of side-effects associated with an arbitrary loss of control flow to {@code
* encloserSummary}.
*/
private void setSideEffectsForControlLoss(AmbiguatedFunctionSummary encloserSummary) {
encloserSummary.setFunctionThrows();
}
@Override
public void enterScope(NodeTraversal t) {
// Nothing to do.
}
@Override
public void exitScope(NodeTraversal t) {
Scope closestContainerScope = t.getScope().getClosestContainerScope();
if (!closestContainerScope.isFunctionScope()) {
// Only functions and the scopes within them are of interest to us.
return;
}
Node function = closestContainerScope.getRootNode();
// Handle deferred local variable modifications:
for (AmbiguatedFunctionSummary sideEffectInfo :
summariesForAllNamesOfFunctionByNode.get(function)) {
checkNotNull(sideEffectInfo, "%s has no side effect info.", function);
if (sideEffectInfo.mutatesGlobalState()) {
continue;
}
for (Var v : t.getScope().getVarIterable()) {
if (v.isParam()
&& !blacklistedVarsByFunction.containsEntry(function, v)
&& taintedVarsByFunction.containsEntry(function, v)) {
sideEffectInfo.setMutatesArguments();
continue;
}
boolean localVar = false;
// Parameters and catch values can come from other scopes.
if (!v.isParam() && !v.isCatch()) {
// TODO(johnlenz): create a useful parameter list
// sideEffectInfo.addKnownLocal(v.getName());
localVar = true;
}
// Take care of locals that might have been tainted.
if (!localVar || blacklistedVarsByFunction.containsEntry(function, v)) {
if (taintedVarsByFunction.containsEntry(function, v)) {
// If the function has global side-effects
// don't bother with the local side-effects.
sideEffectInfo.setMutatesGlobalState();
break;
}
}
}
}
// Clean up memory after exiting out of the function scope where we will no longer need these.
if (t.getScopeRoot().isFunction()) {
blacklistedVarsByFunction.removeAll(function);
taintedVarsByFunction.removeAll(function);
}
}
private boolean isVarDeclaredInSameContainerScope(@Nullable Var v, Scope scope) {
return v != null && v.scope.hasSameContainerScope(scope);
}
/**
* Record information about the side effects caused by assigning a value to a given LHS.
*
* If the operation modifies this or taints global state, mark the enclosing function as
* having those side effects.
*
* @param sideEffectInfo Function side effect record to be updated
* @param scope variable scope in which the variable assignment occurs
* @param enclosingFunction FUNCTION node for the enclosing function
* @param lhsNodes LHS nodes that are all assigned values by a given parent node
* @param hasLocalRhs Predicate indicating whether a given LHS is being assigned a local value
*/
private void visitLhsNodes(
AmbiguatedFunctionSummary sideEffectInfo,
Scope scope,
Node enclosingFunction,
List lhsNodes,
Predicate hasLocalRhs) {
for (Node lhs : lhsNodes) {
if (NodeUtil.isGet(lhs)) {
if (lhs.getFirstChild().isThis()) {
sideEffectInfo.setMutatesThis();
} else {
Node objectNode = lhs.getFirstChild();
if (objectNode.isName()) {
Var var = scope.getVar(objectNode.getString());
if (isVarDeclaredInSameContainerScope(var, scope)) {
// Maybe a local object modification. We won't know for sure until
// we exit the scope and can validate the value of the local.
taintedVarsByFunction.put(enclosingFunction, var);
} else {
sideEffectInfo.setMutatesGlobalState();
}
} else {
// Don't track multi level locals: local.prop.prop2++;
sideEffectInfo.setMutatesGlobalState();
}
}
} else {
checkState(lhs.isName(), lhs);
Var var = scope.getVar(lhs.getString());
if (isVarDeclaredInSameContainerScope(var, scope)) {
if (!hasLocalRhs.test(lhs)) {
// Assigned value is not guaranteed to be a local value,
// so if we see any property assignments on this variable,
// they could be tainting a non-local value.
blacklistedVarsByFunction.put(enclosingFunction, var);
}
} else {
sideEffectInfo.setMutatesGlobalState();
}
}
}
}
/** Record information about a call site. */
private void visitCall(AmbiguatedFunctionSummary callerInfo, Node invocation) {
// Handle special cases (Math, RegExp)
// TODO: This logic can probably be replaced with @nosideeffects annotations in externs.
if (invocation.isCall() && !astAnalyzer.functionCallHasSideEffects(invocation)) {
return;
}
// Handle known cases now (Object, Date, RegExp, etc)
if (invocation.isNew() && !astAnalyzer.constructorCallHasSideEffects(invocation)) {
return;
}
List calleeSummaries = getSummariesForCallee(invocation);
if (calleeSummaries.isEmpty()) {
callerInfo.setAllFlags();
return;
}
for (AmbiguatedFunctionSummary calleeInfo : calleeSummaries) {
SideEffectPropagation edge = SideEffectPropagation.forInvocation(invocation);
reverseCallGraph.connect(calleeInfo.graphNode, edge, callerInfo.graphNode);
}
}
}
private static boolean isInvocationViaCallOrApply(Node callSite) {
Node receiver = callSite.getFirstFirstChild();
if (receiver == null || (!receiver.isName() && !receiver.isGetProp())) {
return false;
}
return NodeUtil.isFunctionObjectCall(callSite) || NodeUtil.isFunctionObjectApply(callSite);
}
private static boolean isCallOrTaggedTemplateLit(Node invocation) {
return invocation.isCall() || invocation.isTaggedTemplateLit();
}
/**
* Returns the unqualified name associated with an R-value.
*
* For NAMEs this is the name. For GETPROPs this is the last segment including a leading dot.
*/
@Nullable
private static String nameForReference(Node nameRef) {
switch (nameRef.getToken()) {
case NAME:
return nameRef.getString();
case GETPROP:
return PROP_NAME_PREFIX + nameRef.getSecondChild().getString();
default:
throw new IllegalStateException("Unexpected name reference: " + nameRef.toStringTree());
}
}
/**
* This class stores all the information about a connection between functions needed to propagate
* side effects from one instance of {@link AmbiguatedFunctionSummary} to another.
*/
private static class SideEffectPropagation {
// Whether this propagation represents an aliasing of one name by another. In that case, all
// side effects of the "callee" just need to be copied onto the "caller".
private final boolean callerIsAlias;
// If all the arguments passed to the callee are local to the caller.
private final boolean allArgsUnescapedLocal;
/*
* If you call a function with apply or call, one of the arguments at the call site will be used
* as 'this' inside the implementation. If this is pass into apply like so: function.apply(this,
* ...) then 'this' in the caller is tainted.
*/
private final boolean calleeThisEqualsCallerThis;
// The token used to invoke the callee by the caller.
@Nullable private final Node invocation;
private SideEffectPropagation(
boolean callerIsAlias,
boolean allArgsUnescapedLocal,
boolean calleeThisEqualsCallerThis,
Node invocation) {
checkArgument(invocation == null || NodeUtil.isInvocation(invocation), invocation);
this.callerIsAlias = callerIsAlias;
this.allArgsUnescapedLocal = allArgsUnescapedLocal;
this.calleeThisEqualsCallerThis = calleeThisEqualsCallerThis;
this.invocation = invocation;
}
static SideEffectPropagation forAlias() {
return new SideEffectPropagation(true, false, false, null);
}
static SideEffectPropagation forInvocation(Node invocation) {
checkArgument(NodeUtil.isInvocation(invocation), invocation);
return new SideEffectPropagation(
false,
NodeUtil.allArgsUnescapedLocal(invocation),
calleeAndCallerShareThis(invocation),
invocation);
}
private static boolean calleeAndCallerShareThis(Node invocation) {
if (!isCallOrTaggedTemplateLit(invocation)) {
return false; // Calling a constructor creates a new object bound to `this`.
}
Node callee = invocation.getFirstChild();
if (callee.isSuper()) {
return true;
}
@Nullable final Node thisArg;
if (isInvocationViaCallOrApply(invocation)) {
// If the call site is actually a `.call` or `.apply`, then `this` will be an argument.
thisArg = invocation.getSecondChild();
} else if (callee.isGetProp()) {
thisArg = callee.getFirstChild();
} else {
thisArg = null;
}
if (thisArg == null) {
return false; // No `this` is being passed.
} else if (thisArg.isThis() || thisArg.isSuper()) {
return true;
}
// TODO(nickreid): If `thisArg` is a known local or known arg we could say something more
// specific about the effect of the callee mutating `this`.
// We're not sure what `this` is being passed, so make a conservative choice.
return false;
}
/**
* Propagate the side effects from the callee to the caller.
*
* @param callee propagate from
* @param caller propagate to
* @return Returns true if the propagation changed the side effects on the caller.
*/
boolean propagate(AmbiguatedFunctionSummary callee, AmbiguatedFunctionSummary caller) {
int initialCallerFlags = caller.bitmask;
if (callerIsAlias) {
caller.setMask(callee.bitmask);
return caller.bitmask != initialCallerFlags;
}
if (callee.mutatesGlobalState()) {
// If the callee modifies global state then so does that caller.
caller.setMutatesGlobalState();
}
if (callee.functionThrows()) {
// If the callee throws an exception then so does the caller.
caller.setFunctionThrows();
}
if (callee.mutatesArguments() && !allArgsUnescapedLocal) {
// If the callee mutates its input arguments and the arguments escape the caller then it has
// unbounded side effects.
caller.setMutatesGlobalState();
}
if (callee.mutatesThis()) {
if (invocation.isNew()) {
// NEWing a constructor provide a unescaped "this" making side-effects impossible.
} else if (calleeThisEqualsCallerThis) {
caller.setMutatesThis();
} else {
caller.setMutatesGlobalState();
}
}
return caller.bitmask != initialCallerFlags;
}
}
/**
* A summary for the set of functions that share a particular name.
*
*
Side-effects of the functions are the most significant aspect of this summary. Because the
* functions are "ambiguated", the recorded side-effects are the union of all side effects
* detected in any member of the set.
*
*
Name in this context refers to a short name, not a qualified name; only the last segment of
* a qualified name is used.
*/
private static final class AmbiguatedFunctionSummary {
// Side effect types:
private static final int THROWS = 1 << 0;
private static final int MUTATES_GLOBAL_STATE = 1 << 1;
private static final int MUTATES_THIS = 1 << 2;
private static final int MUTATES_ARGUMENTS = 1 << 3;
// Function metatdata
private static final int ESCAPED_RETURN = 1 << 4;
// The name shared by the set of functions that defined this summary.
private final String name;
// The node holding this summary in the reverse call graph.
private final DiGraphNode graphNode;
// The side effect flags for this set of functions.
// TODO(nickreid): Replace this with a `Node.SideEffectFlags`.
private int bitmask = 0;
/** Adds a new summary node to {@code graph}, storing the node and returning the summary. */
static AmbiguatedFunctionSummary createInGraph(
DiGraph graph, String name) {
return new AmbiguatedFunctionSummary(graph, name);
}
private AmbiguatedFunctionSummary(
DiGraph graph, String name) {
this.name = checkNotNull(name);
this.graphNode = graph.createDirectedGraphNode(this);
}
private AmbiguatedFunctionSummary setMask(int mask) {
bitmask |= mask;
return this;
}
private boolean getMask(int mask) {
return (bitmask & mask) != 0;
}
boolean mutatesThis() {
return getMask(MUTATES_THIS);
}
/** Marks the function as having "modifies this" side effects. */
AmbiguatedFunctionSummary setMutatesThis() {
return setMask(MUTATES_THIS);
}
/** Returns whether the function returns something that may be affected by global state. */
boolean escapedReturn() {
return getMask(ESCAPED_RETURN);
}
/** Marks the function as having non-local return result. */
AmbiguatedFunctionSummary setEscapedReturn() {
return setMask(ESCAPED_RETURN);
}
/** Returns true if function has an explicit "throw". */
boolean functionThrows() {
return getMask(THROWS);
}
/** Marks the function as having "throw" side effects. */
AmbiguatedFunctionSummary setFunctionThrows() {
return setMask(THROWS);
}
/** Returns true if function mutates global state. */
boolean mutatesGlobalState() {
return getMask(MUTATES_GLOBAL_STATE);
}
/** Marks the function as having "modifies globals" side effects. */
AmbiguatedFunctionSummary setMutatesGlobalState() {
return setMask(MUTATES_GLOBAL_STATE);
}
/** Returns true if function mutates its arguments. */
boolean mutatesArguments() {
return getMask(MUTATES_GLOBAL_STATE | MUTATES_ARGUMENTS);
}
/** Marks the function as having "modifies arguments" side effects. */
AmbiguatedFunctionSummary setMutatesArguments() {
return setMask(MUTATES_ARGUMENTS);
}
AmbiguatedFunctionSummary setAllFlags() {
return setMask(
THROWS | MUTATES_THIS | MUTATES_ARGUMENTS | MUTATES_GLOBAL_STATE | ESCAPED_RETURN);
}
@Override
@DoNotCall // For debugging only.
public String toString() {
return MoreObjects.toStringHelper(getClass())
.add("name", name)
// Passing `graphNode` directly causes recursion as its `toString` calls `toString` on the
// summary it contains.
.add("graphNode", graphNode.hashCode())
.add("sideEffects", sideEffectsToString())
.toString();
}
private String sideEffectsToString() {
List status = new ArrayList<>();
if (mutatesThis()) {
status.add("this");
}
if (mutatesGlobalState()) {
status.add("global");
}
if (mutatesArguments()) {
status.add("args");
}
if (escapedReturn()) {
status.add("return");
}
if (functionThrows()) {
status.add("throw");
}
return status.toString();
}
}
/**
* A compiler pass that constructs a reference graph and drives the PureFunctionIdentifier across
* it.
*/
static final class Driver implements CompilerPass {
private final AbstractCompiler compiler;
Driver(AbstractCompiler compiler) {
this.compiler = compiler;
}
@Override
public void process(Node externs, Node root) {
OptimizeCalls.builder()
.setCompiler(compiler)
.setConsiderExterns(true)
.addPass(new PureFunctionIdentifier(compiler))
.build()
.process(externs, root);
}
}
}