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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.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;

/** Checks for invalid code references to type-only imports (i.e., goog.requireType). */
public final class CheckTypeImportCodeReferences extends AbstractPostOrderCallback
    implements CompilerPass {
  public static final DiagnosticType TYPE_IMPORT_CODE_REFERENCE =
      DiagnosticType.error(
          "JSC_TYPE_IMPORT_CODE_REFERENCE",
          "Cannot reference goog.requireType()''d name {0} outside of a type annotation.");

  private static final Node GOOG_REQUIRE_TYPE =
      IR.getprop(IR.name("goog"), IR.string("requireType"));

  private final AbstractCompiler compiler;

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

  @Override
  public void process(Node externs, Node root) {
    NodeTraversal.traverse(compiler, root, this);
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    if (!n.isName()) {
      return;
    }

    Var var = t.getScope().getVar(n.getString());
    if (var == null) {
      return;
    }

    Node declNameNode = var.getNameNode();

    if (declNameNode == null || declNameNode == n || !NodeUtil.isDeclarationLValue(declNameNode)) {
      return;
    }

    Node decl =
        declNameNode.getParent().isStringKey()
            ? declNameNode.getGrandparent().getGrandparent()
            : declNameNode.getParent();
    if (!NodeUtil.isNameDeclaration(decl)
        || !decl.hasOneChild()
        || !decl.getFirstChild().hasChildren()
        || !decl.getFirstChild().getLastChild().isCall()) {
      return;
    }

    Node callNode = decl.getFirstChild().getLastChild();
    if (!callNode.getFirstChild().matchesQualifiedName(GOOG_REQUIRE_TYPE)) {
      return;
    }

    t.report(n, TYPE_IMPORT_CODE_REFERENCE, n.getString());
  }
}