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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 2020 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.serialization;

import static com.google.common.base.Preconditions.checkState;

import com.google.common.base.Optional;
import com.google.javascript.jscomp.AbstractCompiler;
import com.google.javascript.jscomp.CompilerPass;
import com.google.javascript.jscomp.NodeTraversal;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.jstype.JSType;
import java.util.IdentityHashMap;

/**
 * Pass to convert JSType objects from TypeChecking that are attached to the AST into Color objects
 * whose sole use is to enable running optimizations and delete all other references to JSTypes.
 *
 * This pass is also responsible for logging debug information that needs to know about both
 * JSType objects and their corresponding colors, and for telling the compiler to prepare for
 * reading runtime libraries from precompiled TypedASTs instead of source.
 */
public final class ConvertTypesToColors implements CompilerPass {
  private final AbstractCompiler compiler;
  private final SerializationOptions serializationOptions;

  public ConvertTypesToColors(
      AbstractCompiler compiler, SerializationOptions serializationOptions) {
    this.compiler = compiler;
    this.serializationOptions = serializationOptions;
  }

  private static class RemoveTypes extends AbstractPostOrderCallback {

    RemoveTypes() {}

    @Override
    public void visit(NodeTraversal t, Node n, Node parent) {
      n.setJSType(null);
      n.setJSTypeBeforeCast(null);
      n.setDeclaredTypeExpression(null);
      n.setTypedefTypeProp(null);

      JSDocInfo jsdoc = n.getJSDocInfo();
      if (jsdoc != null) {
        n.setJSDocInfo(JSDocSerializer.convertJSDocInfoForOptimizations(jsdoc));
      }
    }
  }

  private static class RemoveTypesAndApplyColors extends RemoveTypes {
    private final ColorPool.ShardView colorPoolShard;
    private final IdentityHashMap typePointersByJstype;

    RemoveTypesAndApplyColors(
        ColorPool.ShardView colorPoolShard, IdentityHashMap typePointersByJstype) {
      super();
      this.colorPoolShard = colorPoolShard;
      this.typePointersByJstype = typePointersByJstype;
    }

    @Override
    public void visit(NodeTraversal t, Node n, Node parent) {
      JSType oldType = n.getJSType();
      JSType oldTypeBeforeCast = n.getJSTypeBeforeCast();

      super.visit(t, n, parent);

      if (oldType != null) {
        Integer pointer = typePointersByJstype.get(oldType);
        if (pointer != null) {
          n.setColor(colorPoolShard.getColor(pointer));
        }
      }

      if (oldTypeBeforeCast != null) {
        // used by FunctionInjector and InlineVariables when inlining as a hint that a node has a
        // more specific color
        n.setColorFromTypeCast();
      }
    }
  }

  @Override
  public void process(Node externs, Node root) {
    if (compiler.getLifeCycleStage().hasColorAndSimplifiedJSDoc()) {
      // Pass is a no-op if we already have optimization colors or have finished the checks phase
      return;
    }
    // NOTE(lharker): this pass could probably safely run after normalization, except that the
    // LifeCycleStage enum assumes that normalization implies "colors + simplified JSDoc"
    checkState(
        !compiler.getLifeCycleStage().isNormalized(), "Not expected to run after normalization");

    Node externsAndJsRoot = root.getParent();

    if (!compiler.hasTypeCheckingRun()) {
      NodeTraversal.traverse(compiler, externsAndJsRoot, new RemoveTypes());
      compiler.clearJSTypeRegistry();
      this.compiler.initRuntimeLibraryTypedAsts(Optional.absent());
      return;
    }

    StringPool.Builder stringPoolBuilder = StringPool.builder();
    SerializeTypesToPointers serializeJstypes =
        SerializeTypesToPointers.create(compiler, stringPoolBuilder, this.serializationOptions);
    serializeJstypes.gatherTypesOnAst(externsAndJsRoot);

    TypePool typePool = serializeJstypes.getTypePool();
    StringPool stringPool = stringPoolBuilder.build();

    ColorPool.Builder colorPoolBuilder = ColorPool.builder();
    this.compiler.initRuntimeLibraryTypedAsts(Optional.of(colorPoolBuilder));

    RemoveTypesAndApplyColors callback =
        new RemoveTypesAndApplyColors(
            colorPoolBuilder.addShard(typePool, stringPool),
            serializeJstypes.getTypePointersByJstype());

    ColorPool colorPool = colorPoolBuilder.build();
    NodeTraversal.traverse(compiler, externsAndJsRoot, callback);

    compiler.clearJSTypeRegistry();
    compiler.setColorRegistry(colorPool.getRegistry());
  }
}