import com.google.javascript.jscomp.DefinitionsRemover.ExternalNameOnlyDefinition; //导入依赖的package包/类
/**
 * Drop untyped stub definitions (ExternalNameOnlyDefinition) in externs if a typed extern of the
 * same qualified name also exists and has type annotations.
 *
 * <p>TODO: This hack is mostly for the purpose of preventing untyped stubs from showing up in the
 * {@link PureFunctionIdentifier} and causing unknown side effects from propagating everywhere.
 * This should probably be solved in one of the following ways instead:
 *
 * <p>a) Have a pass earlier in the compiler that goes in and removes these stub definitions.
 *
 * <p>b) Fix all extern files so that there are no untyped stubs mixed with typed ones and add a
 * restriction to the compiler to prevent this.
 *
 * <p>c) Drop these stubs in the {@link PureFunctionIdentifier} instead. This "DefinitionProvider"
 * should not have to drop definitions itself.
 */
private void dropUntypedExterns() {
  for (String name : definitionsByName.keySet()) {
    for (Definition definition : new ArrayList<>(definitionsByName.get(name))) {
      if (!(definition instanceof ExternalNameOnlyDefinition)) {
        continue;
      }
      Node definitionNode = definition.getLValue();
      if (jsdocContainsDeclarations(definitionNode)) {
        continue;
      }

      for (Definition previousDefinition : definitionsByName.get(name)) {
        if (previousDefinition != definition
            && definitionNode.matchesQualifiedName(previousDefinition.getLValue())) {
          // *DON'T* remove from definitionNodes since it is desired to retain references to
          // stub definitions.
          definitionsByName.remove(name, definition);
          DefinitionSite definitionSite =
              definitionSitesByDefinitionSiteNode.remove(definitionNode);
          Node scopeNode = NodeUtil.getEnclosingChangeScopeRoot(definitionNode);
          definitionSitesByScopeNode.remove(scopeNode, definitionSite);

          // Since it's a stub we know its keyed by the name/getProp node.
          checkNotNull(definitionSite);
          break;
        }
      }
    }
  }
}