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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 2017 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.deps;

import static com.google.common.collect.ImmutableSet.toImmutableSet;
import static java.util.stream.Collectors.joining;

import com.google.auto.value.AutoValue;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.javascript.jscomp.CheckLevel;
import com.google.javascript.jscomp.DiagnosticType;
import com.google.javascript.jscomp.ErrorHandler;
import com.google.javascript.jscomp.JSError;
import com.google.javascript.jscomp.deps.ModuleLoader.ModuleResolverFactory;
import com.google.javascript.jscomp.deps.ModuleLoader.PathEscaper;
import java.util.Comparator;
import org.jspecify.nullness.Nullable;

/**
 * Limited superset of the {@link BrowserModuleResolver} that allows for replacing some path
 * prefixes before resolving.
 */
public class BrowserWithTransformedPrefixesModuleResolver extends ModuleResolver {

  static final DiagnosticType INVALID_AMBIGUOUS_PATH =
      DiagnosticType.error(
          "JSC_INVALID_AMBIGUOUS_PATH",
          "The path \"{0}\" is invalid. Expected any of the following prefixes for non-relative "
              + "paths: {1}.");

  /** Factory for {@link BrowserWithTransformedPrefixesModuleResolver}. */
  public static final class Factory implements ModuleResolverFactory {
    private final ImmutableMap prefixReplacements;

    public Factory(ImmutableMap prefixReplacements) {
      this.prefixReplacements = prefixReplacements;
    }

    @Override
    public ModuleResolver create(
        ImmutableSet modulePaths,
        ImmutableList moduleRootPaths,
        ErrorHandler errorHandler,
        PathEscaper pathEscaper) {
      return new BrowserWithTransformedPrefixesModuleResolver(
          modulePaths, moduleRootPaths, errorHandler, pathEscaper, prefixReplacements);
    }
  }

  /**
   * Struct of prefix and replacement. Has a natural ordering from longest prefix to shortest
   * prefix.
   */
  @AutoValue
  abstract static class PrefixReplacement {
    abstract String prefix();

    abstract String replacement();

    public static PrefixReplacement of(String prefix, String replacement) {
      return new AutoValue_BrowserWithTransformedPrefixesModuleResolver_PrefixReplacement(
          prefix, replacement);
    }
  }

  private final ImmutableSet prefixReplacements;
  private final String expectedPrefixes;

  public BrowserWithTransformedPrefixesModuleResolver(
      ImmutableSet modulePaths,
      ImmutableList moduleRootPaths,
      ErrorHandler errorHandler,
      PathEscaper pathEscaper,
      ImmutableMap prefixReplacements) {
    super(modulePaths, moduleRootPaths, errorHandler, pathEscaper);
    this.prefixReplacements =
        prefixReplacements.entrySet().stream()
            .map(entry -> PrefixReplacement.of(entry.getKey(), entry.getValue()))
            .sorted(
                // Sort by length in descending order to prefixes are applied most specific to
                // least specific.
                Comparator.comparingInt(r -> r.prefix().length())
                    .reversed()
                    .thenComparing(PrefixReplacement::prefix))
            .collect(toImmutableSet());
    this.expectedPrefixes =
        this.prefixReplacements.stream()
            .map(PrefixReplacement::prefix)
            .sorted()
            .collect(joining(", "));
  }

  @Override
  public @Nullable String resolveJsModule(
      String scriptAddress, String moduleAddress, String sourcename, int lineno, int colno) {
    String transformedAddress = moduleAddress;

    boolean replaced = false;

    for (PrefixReplacement prefixReplacement : prefixReplacements) {
      if (moduleAddress.startsWith(prefixReplacement.prefix())) {
        transformedAddress =
            prefixReplacement.replacement()
                + moduleAddress.substring(prefixReplacement.prefix().length());
        replaced = true;
        break;
      }
    }

    // If ambiguous after the loop it was not transformed and the original moduleAddress is
    // ambiguous with an unrecognized prefix. Allow transformed paths to be ambiguous after
    // transformation to maybe match how files are passed to the compiler.
    if (!replaced && ModuleLoader.isAmbiguousIdentifier(transformedAddress)) {
      errorHandler.report(
          CheckLevel.WARNING,
          JSError.make(
              sourcename,
              lineno,
              colno,
              INVALID_AMBIGUOUS_PATH,
              transformedAddress,
              expectedPrefixes));
      return null;
    }

    String loadAddress = locate(scriptAddress, transformedAddress);
    if (transformedAddress == null) {
      errorHandler.report(
          CheckLevel.WARNING,
          JSError.make(sourcename, lineno, colno, ModuleLoader.LOAD_WARNING, moduleAddress));
    }
    return loadAddress;
  }

  @Override
  public String resolveModuleAsPath(String scriptAddress, String moduleAddress) {
    if (ModuleLoader.isRelativeIdentifier(moduleAddress)) {
      return super.resolveModuleAsPath(scriptAddress, moduleAddress);
    }

    String transformedAddress = moduleAddress;
    for (PrefixReplacement prefixReplacement : prefixReplacements) {
      if (moduleAddress.startsWith(prefixReplacement.prefix())) {
        transformedAddress =
            prefixReplacement.replacement()
                + moduleAddress.substring(prefixReplacement.prefix().length());
        break;
      }
    }

    return ModuleLoader.normalize(transformedAddress, moduleRootPaths);
  }
}