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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 2014 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.refactoring;

import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import com.google.javascript.jscomp.AbstractCompiler;
import com.google.javascript.jscomp.JSError;
import com.google.javascript.jscomp.NodeTraversal;
import com.google.javascript.jscomp.NodeUtil;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Maps a JSError to a SuggestedFix.
 * TODO(tbreisacher): Move this into the compiler itself (i.e. into the jscomp package). This will
 *     make it easier for people adding new warnings to also add fixes for them.
 */
public final class ErrorToFixMapper {
  private ErrorToFixMapper() {} // All static

  private static final Pattern DID_YOU_MEAN = Pattern.compile(".*Did you mean (.*)\\?");
  private static final Pattern MISSING_REQUIRE =
      Pattern.compile("missing require: '([^']+)'");
  private static final Pattern EXTRA_REQUIRE =
      Pattern.compile("extra require: '([^']+)'");

  public static List getFixesForJsError(JSError error, AbstractCompiler compiler) {
    SuggestedFix fix = getFixForJsError(error, compiler);
    if (fix != null) {
      return ImmutableList.of(fix);
    }
    switch (error.getType().key) {
      case "JSC_IMPLICITLY_NULLABLE_JSDOC":
        return getFixesForImplicitlyNullableJsDoc(error);
      default:
        return ImmutableList.of();
    }
  }

  /**
   * Creates a SuggestedFix for the given error. Note that some errors have multiple fixes
   * so getFixesForJsError should often be used instead of this.
   */
  public static SuggestedFix getFixForJsError(JSError error, AbstractCompiler compiler) {
    switch (error.getType().key) {
      case "JSC_MISSING_SEMICOLON":
        return getFixForMissingSemicolon(error);
      case "JSC_REQUIRES_NOT_SORTED":
        return getFixForUnsortedRequiresOrProvides("goog.require", error, compiler);
      case "JSC_PROVIDES_NOT_SORTED":
        return getFixForUnsortedRequiresOrProvides("goog.provide", error, compiler);
      case "JSC_DEBUGGER_STATEMENT_PRESENT":
      case "JSC_USELESS_EMPTY_STATEMENT":
        return removeNode(error);
      case "JSC_INEXISTENT_PROPERTY":
        return getFixForInexistentProperty(error);
      case "JSC_MISSING_CALL_TO_SUPER":
        return getFixForMissingSuper(error);
      case "JSC_INVALID_SUPER_CALL_WITH_SUGGESTION":
        return getFixForInvalidSuper(error, compiler);
      case "JSC_MISSING_REQUIRE_WARNING":
      case "JSC_MISSING_REQUIRE_CALL_WARNING":
        return getFixForMissingRequire(error, compiler);
      case "JSC_DUPLICATE_REQUIRE_WARNING":
      case "JSC_EXTRA_REQUIRE_WARNING":
        return getFixForExtraRequire(error, compiler);
      default:
        return null;
    }
  }

  private static List getFixesForImplicitlyNullableJsDoc(JSError error) {
    SuggestedFix qmark = new SuggestedFix.Builder()
        .setOriginalMatchedNode(error.node)
        .insertBefore(error.node, "?")
        .setDescription("Make nullability explicit")
        .build();
    SuggestedFix bang = new SuggestedFix.Builder()
        .setOriginalMatchedNode(error.node)
        .insertBefore(error.node, "!")
        .setDescription("Make type non-nullable")
        .build();
    return ImmutableList.of(qmark, bang);
  }

  private static SuggestedFix removeNode(JSError error) {
    return new SuggestedFix.Builder()
        .setOriginalMatchedNode(error.node)
        .delete(error.node).build();
  }

  private static SuggestedFix getFixForMissingSemicolon(JSError error) {
    return new SuggestedFix.Builder()
        .setOriginalMatchedNode(error.node)
        .insertAfter(error.node, ";")
        .build();
  }

  private static SuggestedFix getFixForMissingSuper(JSError error) {
    Node body = NodeUtil.getFunctionBody(error.node);
    return new SuggestedFix.Builder()
        .setOriginalMatchedNode(error.node)
        .addChildToFront(body, "super();")
        .build();
  }

  private static SuggestedFix getFixForInvalidSuper(JSError error, AbstractCompiler compiler) {
    Matcher m = DID_YOU_MEAN.matcher(error.description);
    if (m.matches()) {
      return new SuggestedFix.Builder()
          .setOriginalMatchedNode(error.node)
          .replace(error.node, NodeUtil.newQName(compiler, m.group(1)), compiler)
          .build();
    }
    return null;
  }

  private static SuggestedFix getFixForInexistentProperty(JSError error) {
    Matcher m = DID_YOU_MEAN.matcher(error.description);
    if (m.matches()) {
      String suggestedPropName = m.group(1);
      return new SuggestedFix.Builder()
          .setOriginalMatchedNode(error.node)
          .rename(error.node, suggestedPropName).build();
    }
    return null;
  }

  private static SuggestedFix getFixForMissingRequire(JSError error, AbstractCompiler compiler) {
    Matcher regexMatcher = MISSING_REQUIRE.matcher(error.description);
    Preconditions.checkState(regexMatcher.matches(),
        "Unexpected error description: %s", error.description);
    String namespaceToRequire = regexMatcher.group(1);
    NodeMetadata metadata = new NodeMetadata(compiler);
    Match match = new Match(error.node, metadata);
    return new SuggestedFix.Builder()
        .setOriginalMatchedNode(error.node)
        .addGoogRequire(match, namespaceToRequire)
        .build();
  }

  private static SuggestedFix getFixForExtraRequire(JSError error, AbstractCompiler compiler) {
    Matcher regexMatcher = EXTRA_REQUIRE.matcher(error.description);
    Preconditions.checkState(regexMatcher.matches(),
        "Unexpected error description: %s", error.description);
    String namespace = regexMatcher.group(1);
    NodeMetadata metadata = new NodeMetadata(compiler);
    Match match = new Match(error.node, metadata);
    return new SuggestedFix.Builder()
        .setOriginalMatchedNode(error.node)
        .removeGoogRequire(match, namespace)
        .build();
  }

  private static SuggestedFix getFixForUnsortedRequiresOrProvides(
      String closureFunction, JSError error, AbstractCompiler compiler) {
    SuggestedFix.Builder fix = new SuggestedFix.Builder();
    fix.setOriginalMatchedNode(error.node);
    Node script = NodeUtil.getEnclosingScript(error.node);
    RequireProvideSorter cb = new RequireProvideSorter(closureFunction);
    NodeTraversal.traverseEs6(compiler, script, cb);
    Node first = cb.calls.get(0);
    Node last = Iterables.getLast(cb.calls);

    cb.sortCallsAlphabetically();
    StringBuilder sb = new StringBuilder();
    for (Node n : cb.calls) {
      String statement = fix.generateCode(compiler, n);
      JSDocInfo jsDoc = NodeUtil.getBestJSDocInfo(n);
      if (jsDoc != null) {
        statement = jsDoc.getOriginalCommentString() + "\n" + statement;
      }
      sb.append(statement);
    }
    // Trim to remove the newline after the last goog.require/provide.
    String newContent = sb.toString().trim();
    return fix.replaceRange(first, last, newContent).build();
  }

  private static String getNamespaceFromClosureNode(Node exprResult) {
    Preconditions.checkState(exprResult.isExprResult());
    return exprResult.getFirstChild().getLastChild().getString();
  }

  private static class RequireProvideSorter extends NodeTraversal.AbstractShallowCallback
      implements Comparator {
    private final String closureFunction;
    private final List calls = new ArrayList<>();

    RequireProvideSorter(String closureFunction) {
      this.closureFunction = closureFunction;
    }

    @Override
    public final void visit(NodeTraversal nodeTraversal, Node n, Node parent) {
      if (n.isCall()
          && parent.isExprResult()
          && n.getFirstChild().matchesQualifiedName(closureFunction)) {
        calls.add(parent);
      }
    }

    public void sortCallsAlphabetically() {
      Collections.sort(calls, this);
    }

    @Override
    public int compare(Node n1, Node n2) {
      String namespace1 = getNamespaceFromClosureNode(n1);
      String namespace2 = getNamespaceFromClosureNode(n2);
      return namespace1.compareTo(namespace2);
    }
  }
}