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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.lint;

import static com.google.common.collect.ImmutableList.toImmutableList;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import com.google.javascript.jscomp.DiagnosticType;
import com.google.javascript.jscomp.NodeTraversal;
import com.google.javascript.jscomp.NodeUtil;
import com.google.javascript.rhino.Node;
import java.util.ArrayList;
import java.util.List;
import org.jspecify.nullness.Nullable;

/**
 * Checks that goog.provide statements are sorted and deduplicated, exposing the necessary
 * information to produce a suggested fix.
 */
public final class CheckProvidesSorted implements NodeTraversal.Callback {
  public static final DiagnosticType PROVIDES_NOT_SORTED =
      DiagnosticType.warning(
          "JSC_PROVIDES_NOT_SORTED",
          "goog.provide() statements are not sorted."
              + " The correct order is:\n\n{0}\n");

  /** Operation modes. */
  public enum Mode {
    /** Collect information to determine whether a fix is required, but do not report a warning. */
    COLLECT_ONLY,
    /** Additionally report a warning. */
    COLLECT_AND_REPORT
  };

  private final Mode mode;

  // The provided namespaces in the order they appear.
  private final List originalProvides = new ArrayList<>();

  // The provided namespaces in canonical order.
  private @Nullable Node firstNode = null;
  private @Nullable Node lastNode = null;
  private boolean finished = false;

  private @Nullable String replacement = null;
  private boolean needsFix = false;

  public CheckProvidesSorted(Mode mode) {
    this.mode = mode;
  }

  /** Returns the node for the first recognized provide statement. */
  public Node getFirstNode() {
    return firstNode;
  }

  /** Returns the node for the last recognized provide statement. */
  public Node getLastNode() {
    return lastNode;
  }

  /** Returns a textual replacement yielding a canonical version of the provides. */
  public String getReplacement() {
    return replacement;
  }

  /**
   * Returns whether the provides need to be fixed, i.e., whether they are *not* already canonical.
   */
  public boolean needsFix() {
    return needsFix;
  }

  @Override
  public boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
    // Traverse top-level statements until a block of contiguous provides is found.
    return !finished
        && (parent == null || parent.isRoot() || parent.isScript() || parent.isModuleBody());
  }

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

    if (NodeUtil.isGoogProvideCall(n) && areProvideArgumentsValid(n.getFirstChild())) {
      originalProvides.add(getNamespace(n));
      if (firstNode == null) {
        firstNode = lastNode = n;
      } else {
        lastNode = n;
      }
    } else if (!originalProvides.isEmpty()) {
      finished = true;
    }
  }

  private static boolean areProvideArgumentsValid(Node call) {
    return call.hasTwoChildren() && call.getSecondChild().isStringLit();
  }

  private static String getNamespace(Node n) {
    return n.getFirstChild().getSecondChild().getString();
  }

  /** Returns the code for a correctly formatted provide call. */
  private static String formatProvide(String namespace) {
    StringBuilder sb = new StringBuilder();

    sb.append("goog.provide('");
    sb.append(namespace);
    sb.append("');");

    return sb.toString();
  }

  private void checkCanonical(NodeTraversal t) {
    @Nullable
    ImmutableList canonicalProvides =
        originalProvides.stream().distinct().sorted().collect(toImmutableList());
    if (!originalProvides.equals(canonicalProvides)) {
      needsFix = true;
      replacement =
          String.join(
              "\n", Iterables.transform(canonicalProvides, CheckProvidesSorted::formatProvide));
      if (mode == Mode.COLLECT_AND_REPORT) {
        t.report(firstNode, PROVIDES_NOT_SORTED, replacement);
      }
    }
  }
}