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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 2012 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.javascript.jscomp.parsing.parser.FeatureSet.ES5;

import com.google.common.collect.ImmutableList;
import com.google.javascript.jscomp.GlobalVarReferenceMap.GlobalVarRefCleanupPass;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.jstype.FunctionType;
import com.google.javascript.rhino.jstype.JSType;
import java.util.ArrayList;
import java.util.List;

/**
 * Provides passes that should be run before hot-swap/incremental builds.
 */
class CleanupPasses extends PassConfig {

  public CleanupPasses(CompilerOptions options) {
    super(options);
  }

  @Override
  protected List getChecks() {
    List checks = new ArrayList<>();
    checks.add(fieldCleanupPassFactory);
    checks.add(scopeCleanupPassFactory);
    checks.add(globalVarRefCleanupPassFactory);
    return checks;
  }

  @Override
  protected List getOptimizations() {
    return ImmutableList.of();
  }

  final PassFactory fieldCleanupPassFactory =
      PassFactory.builderForHotSwap()
          .setName("FieldCleanupPassFactory")
          .setInternalFactory(FieldCleanupPass::new)
          .setFeatureSet(ES5)
          .build();

  final PassFactory scopeCleanupPassFactory =
      PassFactory.builderForHotSwap()
          .setName("ScopeCleanupPassFactory")
          .setInternalFactory(MemoizedScopeCleanupPass::new)
          .setFeatureSet(ES5)
          .build();

  final PassFactory globalVarRefCleanupPassFactory =
      PassFactory.builderForHotSwap()
          .setName("GlobalVarRefCleanupPassFactory")
          .setInternalFactory(GlobalVarRefCleanupPass::new)
          .setFeatureSet(ES5)
          .build();

  /**
   * A CleanupPass implementation that will remove stored scopes from the
   * TypedScopeCreator of the compiler instance for a the hot swapped script.
   * 
   * This pass will also clear out Source Nodes of Function Types declared on
   * Vars tracked by TypedScopeCreator
   */
  static class MemoizedScopeCleanupPass implements HotSwapCompilerPass {

    private final AbstractCompiler compiler;

    public MemoizedScopeCleanupPass(AbstractCompiler compiler) {
      this.compiler = compiler;
    }

    @Override
    public void hotSwapScript(Node scriptRoot, Node originalRoot) {
      ScopeCreator creator = compiler.getTypedScopeCreator();
      if (creator instanceof TypedScopeCreator) {
        TypedScopeCreator scopeCreator = (TypedScopeCreator) creator;
        String newSrc = scriptRoot.getSourceFileName();
        for (TypedVar var : scopeCreator.getAllSymbols()) {
          JSType type = var.getType();
          if (type != null) {
            FunctionType fnType = type.toMaybeFunctionType();
            if (fnType != null
                && newSrc.equals(NodeUtil.getSourceName(fnType.getSource()))) {
              fnType.setSource(null);
            }
          }
        }
        scopeCreator.removeScopesForScript(originalRoot.getSourceFileName());
      }
    }

    @Override
    public void process(Node externs, Node root) {
      // MemoizedScopeCleanupPass should not do work during process.
    }
  }
}