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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 2015 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.lint;

import com.google.common.collect.ImmutableSet;
import com.google.javascript.jscomp.AbstractCompiler;
import com.google.javascript.jscomp.CompilerPass;
import com.google.javascript.jscomp.DiagnosticType;
import com.google.javascript.jscomp.JSError;
import com.google.javascript.jscomp.NodeTraversal;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.jstype.JSType;
import com.google.javascript.rhino.jstype.JSTypeNative;
import com.google.javascript.rhino.jstype.TemplatizedType;

/**
 * Lints against passing arrays to goog.object methods with the intention of iterating over them as
 * though with a for-in loop, which is discouraged with arrays.
 */
public final class CheckArrayWithGoogObject extends NodeTraversal.AbstractPostOrderCallback
    implements CompilerPass {
  final AbstractCompiler compiler;

  private static final ImmutableSet GOOG_OBJECT_METHODS =
      ImmutableSet.of(
          "goog.object.forEach",
          "goog.object.filter",
          "goog.object.map",
          "goog.object.some",
          "goog.object.every",
          "goog.object.getCount",
          "goog.object.getAnyKey",
          "goog.object.getAnyValue",
          "goog.object.contains",
          "goog.object.getValues",
          "goog.object.getKeys",
          "goog.object.findKey",
          "goog.object.findValue",
          "goog.object.isEmpty",
          "goog.object.clear",
          "goog.object.remove",
          "goog.object.equals",
          "goog.object.clone",
          "goog.object.transpose");

  public static final DiagnosticType ARRAY_PASSED_TO_GOOG_OBJECT =
      DiagnosticType.warning(
          "JSC_ARRAY_PASSED_TO_GOOG_OBJECT",
          "{0} expects an object, not an array. Did you mean to use goog.array?");

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

  public boolean isGoogObjectIterationOverArray(Node n) {
    if (!n.isCall()) {
      return false;
    }
    if (!n.getFirstChild().isQualifiedName()) {
      return false;
    }

    String name = n.getFirstChild().getQualifiedName();
    if (!GOOG_OBJECT_METHODS.contains(name)) {
      return false;
    }

    Node firstArg = n.getSecondChild();
    if (firstArg == null) {
      return false;
    }
    JSType type = firstArg.getJSType();
    return type != null && containsArray(type);
  }

  private boolean containsArray(JSType type) {
    // Check if type is itself an array
    if (type.isArrayType()) {
      return true;
    }
    TemplatizedType templatizedType = type.toMaybeTemplatizedType();
    if (templatizedType != null && templatizedType.getReferencedType().isArrayType()) {
      return true;
    }

    // Check if this is a union that contains an array
    if (type.isUnionType()) {
      JSType arrayType = compiler.getTypeRegistry().getNativeType(JSTypeNative.ARRAY_TYPE);
      for (JSType alternate : type.toMaybeUnionType().getAlternates()) {
        if (alternate.isSubtypeOf(arrayType)) {
          return true;
        }
      }
    }
    return false;
  }

  @Override
  public void visit(NodeTraversal unused, Node n, Node parent) {
    if (isGoogObjectIterationOverArray(n)) {
      compiler.report(
          JSError.make(n, ARRAY_PASSED_TO_GOOG_OBJECT, n.getFirstChild().getQualifiedName()));
    }
  }

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