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Closure Compiler is a JavaScript optimizing compiler. It parses your
JavaScript, analyzes it, removes dead code and rewrites and minimizes
what's left. It also checks syntax, variable references, and types, and
warns about common JavaScript pitfalls. It is used in many of Google's
JavaScript apps, including Gmail, Google Web Search, Google Maps, and
Google Docs.
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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.checkState;
import static com.google.javascript.rhino.jstype.JSTypeNative.UNKNOWN_TYPE;
import static java.util.Comparator.comparingInt;
import com.google.common.collect.HashMultiset;
import com.google.common.collect.Multiset;
import com.google.javascript.jscomp.CodingConvention.AssertionFunctionLookup;
import com.google.javascript.jscomp.DataFlowAnalysis.LinearFlowState;
import com.google.javascript.jscomp.NodeTraversal.AbstractScopedCallback;
import com.google.javascript.jscomp.diagnostic.LogFile;
import com.google.javascript.jscomp.graph.DiGraph.DiGraphNode;
import com.google.javascript.jscomp.type.ReverseAbstractInterpreter;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import com.google.javascript.rhino.jstype.JSType;
import com.google.javascript.rhino.jstype.JSTypeRegistry;
import com.google.javascript.rhino.jstype.JSTypeResolver;
import java.util.Comparator;
import java.util.LinkedHashMap;
import org.jspecify.nullness.Nullable;
/** A compiler pass to run the type inference analysis. */
class TypeInferencePass {
private final AbstractCompiler compiler;
private final JSTypeRegistry registry;
private final ReverseAbstractInterpreter reverseInterpreter;
private TypedScope topScope;
private final TypedScopeCreator scopeCreator;
private final AssertionFunctionLookup assertionFunctionLookup;
// (stepCount, Token) -> populationCount
private final @Nullable LinkedHashMap> stepCountHistogram;
TypeInferencePass(
AbstractCompiler compiler,
ReverseAbstractInterpreter reverseInterpreter,
TypedScopeCreator scopeCreator) {
this.compiler = compiler;
this.registry = compiler.getTypeRegistry();
this.reverseInterpreter = reverseInterpreter;
this.scopeCreator = scopeCreator;
this.assertionFunctionLookup =
AssertionFunctionLookup.of(compiler.getCodingConvention().getAssertionFunctions());
this.stepCountHistogram = compiler.isDebugLoggingEnabled() ? new LinkedHashMap<>() : null;
}
/**
* Execute type inference running over part of the scope tree.
*
* @return the top scope, either newly created, or patched by this inference.
*/
TypedScope inferAllScopes(Node inferenceRoot) {
// Type analysis happens in two major phases.
// 1) Finding all the symbols.
// 2) Propagating all the inferred types.
//
// The order of this analysis is non-obvious. In a complete inference
// system, we may need to backtrack arbitrarily far. But the compile-time
// costs would be unacceptable.
//
// We do one pass where we do typed scope creation for all scopes
// in pre-order.
//
// Then we do a second pass where we do all type inference
// (type propagation) in pre-order.
//
// We use a memoized scope creator so that we never create a scope
// more than once.
//
// This will allow us to handle cases like:
// var ns = {};
// (function() { /** JSDoc */ ns.method = function() {}; })();
// ns.method();
// In this code, we need to build the symbol table for the inner scope in
// order to propagate the type of ns.method in the outer scope.
try (JSTypeResolver.Closer closer = this.registry.getResolver().openForDefinition()) {
checkState(inferenceRoot.isRoot());
checkState(inferenceRoot.getParent() == null);
checkState(this.topScope == null);
this.topScope = scopeCreator.createScope(inferenceRoot, null);
NodeTraversal.builder()
.setCompiler(compiler)
.setCallback(new FirstScopeBuildingCallback())
.setScopeCreator(scopeCreator)
.traverseWithScope(inferenceRoot, this.topScope);
scopeCreator.resolveWeakImportsPreResolution();
}
scopeCreator.finishAndFreeze();
NodeTraversal.builder()
.setCompiler(compiler)
.setCallback(new SecondScopeBuildingCallback())
.setScopeCreator(scopeCreator)
.traverseWithScope(inferenceRoot, this.topScope);
// Normalize TypedVars to have the '?' type instead of null after inference is complete. This
// currently cannot be done any earlier because it breaks inference of variables assigned in
// local scopes.
// TODO(b/149843534): this should be a crash instead.
final JSType unknownType = this.registry.getNativeType(UNKNOWN_TYPE);
for (TypedVar var : this.scopeCreator.getAllSymbols()) {
if (var.getType() == null) {
var.setType(unknownType);
}
}
if (this.stepCountHistogram != null) {
try (LogFile histogram =
this.compiler.createOrReopenLog(this.getClass(), "step_histogram.log")) {
histogram.log("step_count token population");
int[] totals = new int[] {0, 0};
this.stepCountHistogram.keySet().stream()
.sorted(Comparator.naturalOrder().reversed())
.forEach(
(stepCount) ->
this.stepCountHistogram.get(stepCount).entrySet().stream()
.sorted(comparingInt(Multiset.Entry::getCount))
.forEach(
(e) -> {
totals[0] += stepCount * e.getCount();
totals[1] += e.getCount();
histogram.log("%s %s %s", stepCount, e.getElement(), e.getCount());
}));
histogram.log("%s TOTAL %s", totals[0], totals[1]);
}
}
return this.topScope;
}
private void inferScope(Node n, TypedScope scope) {
ControlFlowGraph cfg = computeCfg(n);
TypeInference typeInference =
new TypeInference(
compiler, cfg, reverseInterpreter, scope, scopeCreator, assertionFunctionLookup);
typeInference.analyze();
if (this.stepCountHistogram != null) {
for (DiGraphNode node : cfg.getNodes()) {
if (node == cfg.getImplicitReturn()) {
continue;
}
LinearFlowState state = node.getAnnotation();
this.stepCountHistogram
.computeIfAbsent(state.getStepCount(), (k) -> HashMultiset.create())
.add(node.getValue().getToken());
}
}
}
private static class FirstScopeBuildingCallback extends AbstractScopedCallback {
@Override
public void enterScope(NodeTraversal t) {
t.getTypedScope();
}
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
// Do nothing
}
}
private class SecondScopeBuildingCallback extends AbstractScopedCallback {
@Override
public void enterScope(NodeTraversal t) {
// Only infer the entry root, rather than the scope root.
// This ensures that incremental compilation only touches the root
// that's been swapped out.
TypedScope scope = t.getTypedScope();
if (scope.isCfgRootScope() && !scope.isModuleScope()) {
// ignore scopes that don't have their own CFGs and module scopes, which are visited
// as if they were a regular script.
inferScope(t.getCurrentNode(), scope);
}
}
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
// Do nothing
}
}
private ControlFlowGraph computeCfg(Node n) {
return ControlFlowAnalysis.builder()
.setCompiler(compiler)
.setCfgRoot(n)
.setIncludeEdgeAnnotations(true)
.computeCfg();
}
}