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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.jscomp;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.javascript.jscomp.CheckRegExp.MALFORMED_REGEXP;

import com.google.common.annotations.VisibleForTesting;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.jscomp.parsing.Config.LanguageMode;
import com.google.javascript.jscomp.parsing.parser.FeatureSet;
import com.google.javascript.jscomp.parsing.parser.FeatureSet.Feature;
import com.google.javascript.jscomp.regex.RegExpTree;
import com.google.javascript.jscomp.regex.RegExpTree.LookbehindAssertion;
import com.google.javascript.jscomp.regex.RegExpTree.NamedCaptureGroup;
import com.google.javascript.jscomp.regex.RegExpTree.UnicodePropertyEscape;
import com.google.javascript.rhino.Node;
import java.util.function.Predicate;

/**
 * Looks for presence of features that are not supported for transpilation (mostly new RegExp
 * features). Reports errors for any features are present in the root and not present in the
 * targeted output language.
 */
public final class MarkUntranspilableFeaturesAsRemoved extends AbstractPostOrderCallback
    implements CompilerPass {

  @VisibleForTesting
  public static final DiagnosticType UNTRANSPILABLE_FEATURE_PRESENT =
      DiagnosticType.error(
          "JSC_UNTRANSPILABLE",
          // TODO(b/123768968) suggest users raise their language level once we support language
          // output higher than ES5.
          "Cannot convert {0} feature \"{1}\" to targeted output language.");

  private static final FeatureSet UNTRANSPILABLE_2018_FEATURES =
      FeatureSet.BARE_MINIMUM.with(
          Feature.REGEXP_FLAG_S,
          Feature.REGEXP_LOOKBEHIND,
          Feature.REGEXP_NAMED_GROUPS,
          Feature.REGEXP_UNICODE_PROPERTY_ESCAPE);

  private static final FeatureSet UNTRANSPILABLE_2019_FEATURES =
      FeatureSet.BARE_MINIMUM.with(
          // We could transpile this, but there's no point. We always escape these in the output,
          // no need to have a separate pass to escape them. So we'll piggy back off this pass to
          // mark it as transpiled. Note that we never complain that this feature won't be
          // transpiled below.
          Feature.UNESCAPED_UNICODE_LINE_OR_PARAGRAPH_SEP);

  private static final FeatureSet UNTRANSPILABLE_2022_FEATURES =
      FeatureSet.BARE_MINIMUM.with(Feature.REGEXP_FLAG_D);

  private static final FeatureSet ALL_UNTRANSPILABLE_FEATURES =
      FeatureSet.BARE_MINIMUM
          .union(UNTRANSPILABLE_2018_FEATURES)
          .union(UNTRANSPILABLE_2019_FEATURES)
          .union(UNTRANSPILABLE_2022_FEATURES);

  private final AbstractCompiler compiler;
  private final FeatureSet untranspilableFeaturesToRemove;

  MarkUntranspilableFeaturesAsRemoved(AbstractCompiler compiler, FeatureSet outputFeatures) {
    checkNotNull(compiler);
    checkNotNull(outputFeatures);
    this.compiler = compiler;
    this.untranspilableFeaturesToRemove =
        ALL_UNTRANSPILABLE_FEATURES // Features that we can't transpile...
            .without(outputFeatures); // and do not exist in the output language features
  }

  @Override
  public void process(Node externs, Node root) {
    checkForUntranspilable(root);
  }

  private void checkForUntranspilable(Node root) {
    // Non-flag RegExp features are not attached to nodes, so we must force traversal.
    NodeTraversal.traverse(compiler, root, this);
    TranspilationPasses.maybeMarkFeaturesAsTranspiledAway(compiler, untranspilableFeaturesToRemove);
  }

  private void reportUntranspilable(Feature feature, Node node) {
    compiler.report(
        JSError.make(
            node,
            UNTRANSPILABLE_FEATURE_PRESENT,
            LanguageMode.minimumRequiredFor(feature).toString(),
            feature.toString()));
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    switch (n.getToken()) {
      case REGEXP:
        {
          String pattern = n.getFirstChild().getString();
          String flags = n.hasTwoChildren() ? n.getLastChild().getString() : "";
          RegExpTree reg;
          try {
            reg = RegExpTree.parseRegExp(pattern, flags);
          } catch (IllegalArgumentException | IndexOutOfBoundsException ex) {
            t.report(n, MALFORMED_REGEXP, ex.getMessage());
            break;
          }
          if (untranspilableFeaturesToRemove.contains(Feature.REGEXP_FLAG_S)) {
            checkForRegExpSFlag(n);
          }
          if (untranspilableFeaturesToRemove.contains(Feature.REGEXP_LOOKBEHIND)) {
            checkForLookbehind(n, reg);
          }
          if (untranspilableFeaturesToRemove.contains(Feature.REGEXP_NAMED_GROUPS)) {
            checkForNamedGroups(n, reg);
          }
          if (untranspilableFeaturesToRemove.contains(Feature.REGEXP_UNICODE_PROPERTY_ESCAPE)) {
            checkForUnicodePropertyEscape(n, reg);
          }
          if (untranspilableFeaturesToRemove.contains(Feature.REGEXP_FLAG_D)) {
            checkForRegExpDFlag(n);
          }
          break;
        }

      default:
        break;
    }
  }

  private void checkForRegExpSFlag(Node regexpNode) {
    checkArgument(regexpNode.isRegExp());
    String flags = regexpNode.hasTwoChildren() ? regexpNode.getLastChild().getString() : "";
    if (flags.contains("s")) {
      reportUntranspilable(Feature.REGEXP_FLAG_S, regexpNode);
    }
  }

  private void checkForLookbehind(Node regexpNode, RegExpTree tree) {
    checkArgument(regexpNode != null);
    if (anySubtreeMeetsPredicate(tree, t -> t instanceof LookbehindAssertion)) {
      reportUntranspilable(Feature.REGEXP_LOOKBEHIND, regexpNode);
    }
  }

  private void checkForNamedGroups(Node regexpNode, RegExpTree tree) {
    checkArgument(regexpNode != null);
    if (anySubtreeMeetsPredicate(tree, t -> t instanceof NamedCaptureGroup)) {
      reportUntranspilable(Feature.REGEXP_NAMED_GROUPS, regexpNode);
    }
  }

  private void checkForUnicodePropertyEscape(Node regexpNode, RegExpTree tree) {
    checkArgument(regexpNode != null);
    if (anySubtreeMeetsPredicate(tree, t -> t instanceof UnicodePropertyEscape)) {
      reportUntranspilable(Feature.REGEXP_UNICODE_PROPERTY_ESCAPE, regexpNode);
    }
  }

  private void checkForRegExpDFlag(Node regexpNode) {
    checkArgument(regexpNode.isRegExp());
    String flags = regexpNode.hasTwoChildren() ? regexpNode.getLastChild().getString() : "";
    if (flags.contains("d")) {
      reportUntranspilable(Feature.REGEXP_FLAG_D, regexpNode);
    }
  }

  private static boolean anySubtreeMeetsPredicate(RegExpTree tree, Predicate p) {
    if (p.test(tree)) {
      return true;
    }
    for (RegExpTree subTree : tree.children()) {
      if (anySubtreeMeetsPredicate(subTree, p)) {
        return true;
      }
    }
    return false;
  }

}