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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.base.Function;
import com.google.common.base.Preconditions;
import com.google.common.collect.Ordering;
import com.google.javascript.jscomp.AbstractCompiler;
import com.google.javascript.jscomp.DiagnosticType;
import com.google.javascript.jscomp.HotSwapCompilerPass;
import com.google.javascript.jscomp.NodeTraversal;
import com.google.javascript.jscomp.NodeTraversal.AbstractShallowCallback;
import com.google.javascript.jscomp.NodeUtil;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;

import java.util.ArrayList;
import java.util.List;

/**
 * Checks that goog.require() and goog.provide() calls are sorted alphabetically.
 */
public final class CheckRequiresAndProvidesSorted extends AbstractShallowCallback
    implements HotSwapCompilerPass {
  public static final DiagnosticType REQUIRES_NOT_SORTED =
      DiagnosticType.warning(
          "JSC_REQUIRES_NOT_SORTED", "goog.require() statements are not sorted.");

  public static final DiagnosticType PROVIDES_NOT_SORTED =
      DiagnosticType.warning(
          "JSC_PROVIDES_NOT_SORTED", "goog.provide() statements are not sorted.");

  public static final DiagnosticType PROVIDES_AFTER_REQUIRES =
      DiagnosticType.warning(
          "JSC_PROVIDES_AFTER_REQUIRES",
          "goog.provide() statements should be before goog.require() statements.");

  private List requires;
  private List provides;
  private boolean containsShorthandRequire = false;

  private final AbstractCompiler compiler;

  public CheckRequiresAndProvidesSorted(AbstractCompiler compiler) {
    this.compiler = compiler;
    this.requires = new ArrayList<>();
    this.provides = new ArrayList<>();
  }

  @Override
  public void process(Node externs, Node root) {
    NodeTraversal.traverseEs6(compiler, root, this);
  }

  @Override
  public void hotSwapScript(Node scriptRoot, Node originalRoot) {
    NodeTraversal.traverseEs6(compiler, scriptRoot, this);
  }

  private final Function getNamespace =
      new Function() {
        @Override
        public String apply(Node n) {
          Preconditions.checkState(n.isCall(), n);
          return n.getLastChild().getString();
        }
      };

  private final Ordering alphabetical = Ordering.natural().onResultOf(getNamespace);

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    switch (n.getType()) {
      case Token.SCRIPT:
        // For now, don't report any sorting-related warnings if there are
        // "var x = goog.require('goog.x');" style requires.
        if (!containsShorthandRequire) {
          if (!alphabetical.isOrdered(requires)) {
            t.report(requires.get(0), REQUIRES_NOT_SORTED);
          }
          if (!alphabetical.isOrdered(provides)) {
            t.report(provides.get(0), PROVIDES_NOT_SORTED);
          }
        }
        requires.clear();
        provides.clear();
        containsShorthandRequire = false;
        break;
      case Token.CALL:
        Node callee = n.getFirstChild();
        if (!callee.matchesQualifiedName("goog.require")
            && !callee.matchesQualifiedName("goog.provide")
            && !callee.matchesQualifiedName("goog.module")) {
          return;
        }

        if (parent.isExprResult() && parent.getParent().isScript()) {
          String namespace = n.getLastChild().getString();
          if (namespace == null) {
            return;
          }
          if (callee.matchesQualifiedName("goog.require")) {
            requires.add(n);
          } else {
            if (!requires.isEmpty()) {
              t.report(n, PROVIDES_AFTER_REQUIRES);
            }
            if (callee.matchesQualifiedName("goog.provide")) {
              provides.add(n);
            }
          }
        } else if (NodeUtil.isNameDeclaration(parent.getParent())
            && callee.matchesQualifiedName("goog.require")) {
          containsShorthandRequire = true;
        }
        break;
    }
  }
}