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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 2016 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.checkNotNull;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.javascript.jscomp.deps.DependencyInfo;
import com.google.javascript.jscomp.deps.ModuleLoader;
import com.google.javascript.jscomp.parsing.parser.FeatureSet;
import com.google.javascript.jscomp.parsing.parser.FeatureSet.Feature;
import java.util.Map;
import java.util.TreeMap;
import org.jspecify.nullness.Nullable;

/** A DependencyInfo class that determines load flags by parsing the AST just-in-time. */
public class LazyParsedDependencyInfo implements DependencyInfo {

  private final DependencyInfo delegate;
  private @Nullable JsAst ast;
  private final transient AbstractCompiler compiler;

  private ImmutableMap loadFlags;

  public LazyParsedDependencyInfo(DependencyInfo delegate, JsAst ast, AbstractCompiler compiler) {
    this.delegate = checkNotNull(delegate);
    this.ast = checkNotNull(ast);
    this.compiler = checkNotNull(compiler);
  }

  @Override
  public boolean isEs6Module() {
    // Instead of doing a full parse to read all load flags, just ask the delegate, which at least
    // has this much info
    return delegate.isEs6Module();
  }

  @Override
  public boolean isGoogModule() {
    // Instead of doing a full parse to read all load flags, just ask the delegate, which at least
    // has this much info
    return delegate.isGoogModule();
  }

  @Override
  public ImmutableMap getLoadFlags() {
    if (loadFlags == null) {
      Map loadFlagsBuilder = new TreeMap<>();
      boolean hadSourceInMemory = ast.getSourceFile().hasSourceInMemory();
      loadFlagsBuilder.putAll(delegate.getLoadFlags());
      FeatureSet features = ast.getFeatures(compiler);
      if (features.has(Feature.MODULES)) {
        String previousModule = loadFlagsBuilder.get("module");
        if (previousModule != null && !previousModule.equals("es6")) {
          compiler.report(
              JSError.make(
                  getName(),
                  /* lineno= */ -1,
                  /* charno= */ -1,
                  ModuleLoader.MODULE_CONFLICT,
                  getName()));
        }
        loadFlagsBuilder.put("module", "es6");
      }
      String version = features.version();
      if (!version.equals("es3")) {
        loadFlagsBuilder.put("lang", version);
      }
      loadFlags = ImmutableMap.copyOf(loadFlagsBuilder);

      // Don't preserve the source in memory if it was loaded only for getLoadFlags().
      if (!hadSourceInMemory) {
        ast.getSourceFile().clearCachedSource();
      }
      // Don't preserve the full AST longer than necessary.  It can consume a lot of memory.
      ast = null;
    }
    return loadFlags;
  }

  @Override
  public String getName() {
    return delegate.getName();
  }

  @Override
  public String getPathRelativeToClosureBase() {
    return delegate.getPathRelativeToClosureBase();
  }

  @Override
  public ImmutableList getRequires() {
    return delegate.getRequires();
  }

  @Override
  public ImmutableList getTypeRequires() {
    return delegate.getTypeRequires();
  }

  @Override
  public ImmutableList getProvides() {
    return delegate.getProvides();
  }

  @Override
  public boolean getHasExternsAnnotation() {
    return delegate.getHasExternsAnnotation();
  }

  @Override
  public boolean getHasNoCompileAnnotation() {
    return delegate.getHasNoCompileAnnotation();
  }
}