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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 2019 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.common.collect.ImmutableSet;
import com.google.javascript.jscomp.modules.Module;
import com.google.javascript.jscomp.modules.ModuleMap;
import com.google.javascript.rhino.Node;
import javax.annotation.Nullable;

/**
 * Resolves module requires into {@link TypedVar}s.
 *
 * Currently this only supports goog.modules, but can be extended for ES modules.
 */
final class ModuleImportResolver {

  private final ModuleMap moduleMap;

  private static final String GOOG = "goog";
  private static final ImmutableSet googDependencyCalls =
      ImmutableSet.of("require", "requireType", "forwardDeclare");

  ModuleImportResolver(ModuleMap moduleMap) {
    this.moduleMap = moduleMap;
  }

  /** Returns whether this is a CALL node for goog.require(Type) or goog.forwardDeclare */
  boolean isGoogModuleDependencyCall(Node value) {
    if (value == null || !value.isCall()) {
      return false;
    }
    Node callee = value.getFirstChild();
    if (!callee.isGetProp()) {
      return false;
    }
    Node owner = callee.getFirstChild();
    Node property = callee.getSecondChild();
    return owner.isName()
        && owner.getString().equals(GOOG)
        && googDependencyCalls.contains(property.getString());
  }

  /**
   * Attempts to look up the type of a Closure namespace from a require call
   *
   * This returns null if the given {@link ModuleMap} is null, if the required module does not
   * exist, or if support is missing for the type of required {@link Module}. Currently only
   * requires of other goog.modules are supported.
   *
   * @param googRequire a CALL node representing some kind of Closure require.
   */
  ScopedName getClosureNamespaceTypeFromCall(Node googRequire) {
    if (moduleMap == null) {
      // TODO(b/124919359): make sure all tests have generated a ModuleMap
      return null;
    }
    String moduleId = googRequire.getSecondChild().getString();
    Module module = moduleMap.getClosureModule(moduleId);
    if (module == null) {
      return null;
    }

    Node scopeRoot = getModuleScopeRoot(module);
    if (scopeRoot != null) {
      return ScopedName.of("exports", scopeRoot);
    }
    // TODO(b/124919359): assert that this is non-nullable once getModuleScopeRoot handles modules
    // other than goog.modules.
    return null;
  }

  /** Converts a {@link Module} reference to a {@link Node} scope root. */
  @Nullable
  private Node getModuleScopeRoot(@Nullable Module module) {
    if (!module.metadata().isGoogModule()) {
      // TODO(b/124919359): also handle ES modules and goog.provides
      return null;
    }
    Node scriptNode = module.metadata().rootNode();

    if (scriptNode.isScript()
        && scriptNode.hasOneChild()
        && scriptNode.getOnlyChild().isModuleBody()) {
      // The module root node should be a SCRIPT, whose first child is a MODULE_BODY.
      // The map is keyed off a MODULE_BODY node for a goog.module,
      // which is the only child of our SCRIPT node.
      return scriptNode.getOnlyChild();
    } else if (scriptNode.isCall()) {
      // This is a goog.loadModule call, and the scope is keyed off the FUNCTION node's BLOCK in:
      //   goog.loadModule(function(exports)
      Node functionLiteral = scriptNode.getSecondChild();
      return NodeUtil.getFunctionBody(functionLiteral);
    }
    // TODO(b/124919359): this case should not happen, but is triggering on goog.require calls in
    // rewritten modules with preserveClosurePrimitives enabled.
    return null;
  }
}