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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 2014 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 com.google.javascript.rhino.Node;

/**
 * Adds runtime libraries to the beginning of the AST. The libraries for runtime typechecking are
 * added, if needed, as well as any other libraries explicitly requested via the {@link
 * CompilerOptions#forceLibraryInjection} field.
 *
 * TODO(b/120486392): merge this pass with {@link InjectTranspilationRuntimeLibraries}.
 */
class InjectRuntimeLibraries implements CompilerPass {
  private final AbstractCompiler compiler;
  private final Stage stage;
  // The runtime type check library code is special in that it is the only library that should be
  // injected before typechecking. All other library code is expected to be injected during the
  // optimization phase. This is because runtime typechecking is incompatible with a binary reading
  // from precompiled TypedASTs.
  private static final String RUNTIME_TYPE_CHECK_LIB = "runtime_type_check";

  private enum Stage {
    CHECKS,
    OPTIMIZATIONS
  }

  private InjectRuntimeLibraries(AbstractCompiler compiler, Stage stage) {
    this.compiler = compiler;
    this.stage = stage;
  }

  @Override
  public void process(Node externs, Node root) {
    // TODO(bradfordcsmith): Passes should not read the compiler options object.
    CompilerOptions options = compiler.getOptions();
    switch (this.stage) {
      case CHECKS:
        injectCheckLibraries(options);
        return;
      case OPTIMIZATIONS:
        injectOptimizationsLibraries(options);
        return;
    }
    throw new AssertionError();
  }

  private void injectCheckLibraries(CompilerOptions options) {
    if (options.runtimeTypeCheck
        || options.forceLibraryInjection.contains(RUNTIME_TYPE_CHECK_LIB)) {
      compiler.ensureLibraryInjected(RUNTIME_TYPE_CHECK_LIB, true);
    }
  }

  private void injectOptimizationsLibraries(CompilerOptions options) {
    for (String forced : options.forceLibraryInjection) {
      if (!forced.equals(RUNTIME_TYPE_CHECK_LIB)) {
        compiler.ensureLibraryInjected(forced, true);
      }
    }
  }

  public static InjectRuntimeLibraries forChecks(AbstractCompiler compiler) {
    return new InjectRuntimeLibraries(compiler, Stage.CHECKS);
  }

  public static InjectRuntimeLibraries forOptimizations(AbstractCompiler compiler) {
    return new InjectRuntimeLibraries(compiler, Stage.OPTIMIZATIONS);
  }
}