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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 2018 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.modules;

import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Sets;
import com.google.javascript.jscomp.AbstractCompiler;
import com.google.javascript.jscomp.CompilerPass;
import com.google.javascript.jscomp.DiagnosticType;
import com.google.javascript.jscomp.deps.ModuleLoader.ModulePath;
import com.google.javascript.jscomp.modules.ModuleMetadataMap.ModuleMetadata;
import com.google.javascript.jscomp.modules.ModuleMetadataMap.ModuleType;
import com.google.javascript.rhino.Node;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import org.jspecify.nullness.Nullable;

/** Creates a {@link ModuleMap}. */
public class ModuleMapCreator implements CompilerPass {
  public static final DiagnosticType DOES_NOT_HAVE_EXPORT =
      DiagnosticType.error(
          "JSC_DOES_NOT_HAVE_EXPORT", "Requested module does not have an export \"{0}\".");

  public static final DiagnosticType DOES_NOT_HAVE_EXPORT_WITH_DETAILS =
      DiagnosticType.error(
          "JSC_DOES_NOT_HAVE_EXPORT_WITH_DETAILS",
          "Requested module does not have an export \"{0}\".{1}");

  private final class ModuleRequestResolverImpl implements ModuleRequestResolver {
    private UnresolvedModule getFallbackForMissingNonClosureModule(ModulePath path) {
      ModuleMetadata metadata =
          ModuleMetadata.builder()
              .rootNode(null)
              .path(path)
              .moduleType(ModuleType.ES6_MODULE)
              .isTestOnly(false)
              .usesClosure(false)
              .build();

      return new UnresolvedModule() {
        @Override
        void reset() {}

        @Override
        Module resolve(
            ModuleRequestResolver moduleRequestResolver, @Nullable String moduleSpecifier) {
          return Module.builder()
              .boundNames(ImmutableMap.of())
              .namespace(ImmutableMap.of())
              .localNameToLocalExport(ImmutableMap.of())
              .path(path)
              .metadata(metadata)
              .build();
        }

        @Override
        ModuleMetadata metadata() {
          return metadata;
        }

        @Override
        ImmutableSet getExportedNames(ModuleRequestResolver moduleRequestResolver) {
          return ImmutableSet.of();
        }

        @Override
        protected ImmutableSet getExportedNames(
            ModuleRequestResolver moduleRequestResolver, Set visited) {
          return ImmutableSet.of();
        }

        @Override
        ResolveExportResult resolveExport(
            ModuleRequestResolver moduleRequestResolver,
            @Nullable String moduleSpecifier,
            String exportName,
            Set resolveSet,
            Set exportStarSet) {
          return ResolveExportResult.of(
              Binding.from(
                  Export.builder()
                      .localName(exportName)
                      .moduleMetadata(metadata)
                      .modulePath(path)
                      .closureNamespace(null)
                      .build(),
                  /* sourceNode= */ null));
        }
      };
    }

    private UnresolvedModule getFallbackForMissingClosureModule(String namespace) {
      return nonEsModuleProcessor.process(
          ModuleMetadata.builder()
              .addGoogNamespace(namespace)
              .isTestOnly(false)
              .moduleType(ModuleType.GOOG_PROVIDE)
              .path(null)
              .rootNode(null)
              .usesClosure(true)
              .build(),
          /* path= */ null,
          /* script= */ null);
    }

    @Override
    public @Nullable UnresolvedModule resolve(Import i) {
      if (i.modulePath() == null) {
        return resolveForClosure(i.moduleRequest());
      }
      return resolve(i.moduleRequest(), i.modulePath(), i.importNode());
    }

    @Override
    public @Nullable UnresolvedModule resolve(Export e) {
      return resolve(e.moduleRequest(), e.modulePath(), e.exportNode());
    }

    private @Nullable UnresolvedModule resolveForClosure(String namespace) {
      return unresolvedModulesByClosureNamespace.computeIfAbsent(
          namespace, this::getFallbackForMissingClosureModule);
    }

    private @Nullable UnresolvedModule resolve(
        String moduleRequest, ModulePath modulePath, Node forLineInfo) {

      if (GoogEsImports.isGoogImportSpecifier(moduleRequest)) {
        String namespace = GoogEsImports.getClosureIdFromGoogImportSpecifier(moduleRequest);
        return resolveForClosure(namespace);
      }

      ModulePath requestedPath =
          modulePath.resolveJsModule(
              moduleRequest,
              forLineInfo.getSourceFileName(),
              forLineInfo.getLineno(),
              forLineInfo.getCharno());

      if (requestedPath == null) {
        requestedPath = modulePath.resolveModuleAsPath(moduleRequest);

        if (!unresolvedModules.containsKey(requestedPath.toModuleName())) {
          UnresolvedModule module = getFallbackForMissingNonClosureModule(requestedPath);
          unresolvedModules.put(requestedPath.toModuleName(), module);
          return module;
        }
      }

      return unresolvedModules.get(requestedPath.toModuleName());
    }
  }

  /** A basic interface that can scan and return information about a module. */
  interface ModuleProcessor {
    UnresolvedModule process(ModuleMetadata metadata, ModulePath path, Node script);
  }

  private final AbstractCompiler compiler;
  private final EsModuleProcessor esModuleProcessor;
  private final ClosureModuleProcessor closureModuleProcessor;
  private final NonEsModuleProcessor nonEsModuleProcessor;
  private final Map unresolvedModules;
  private final Map unresolvedModulesByClosureNamespace;
  private final ModuleMetadataMap moduleMetadataMap;

  public ModuleMapCreator(AbstractCompiler compiler, ModuleMetadataMap moduleMetadataMap) {
    this.compiler = compiler;
    this.moduleMetadataMap = moduleMetadataMap;
    this.esModuleProcessor = new EsModuleProcessor(compiler);
    this.closureModuleProcessor = new ClosureModuleProcessor(compiler);
    this.nonEsModuleProcessor = new NonEsModuleProcessor();
    unresolvedModules = new HashMap<>();
    unresolvedModulesByClosureNamespace = new HashMap<>();
  }

  private ModuleMap create() {
    unresolvedModules.clear();
    unresolvedModulesByClosureNamespace.clear();

    // There are modules that aren't associated with scripts - nested goog.modules in
    // goog.loadModule calls.
    for (ModuleMetadata moduleMetadata : moduleMetadataMap.getAllModuleMetadata()) {
      process(moduleMetadata);
    }

    return resolve();
  }

  private ModuleMap resolve() {
    ModuleRequestResolver requestResolver = new ModuleRequestResolverImpl();
    Map resolvedModules = new HashMap<>();
    Map resolvedClosureModules = new HashMap<>();

    // We need to resolve in a loop as any missing reference will add a fake to the
    // unresolvedModules map (see getFallback* methods above). This would cause a concurrent
    // modification exception if we just iterated over unresolvedModules. So the first loop through
    // should resolve any "known" modules, and the second any "unrecognized" modules.
    do {
      ImmutableSet toResolve =
          Sets.difference(unresolvedModules.keySet(), resolvedModules.keySet()).immutableCopy();

      for (String key : toResolve) {
        Module resolved = unresolvedModules.get(key).resolve(requestResolver);
        resolvedModules.put(key, resolved);

        for (String namespace : resolved.metadata().googNamespaces()) {
          resolvedClosureModules.put(namespace, resolved);
        }
      }

    } while (!resolvedModules.keySet().containsAll(unresolvedModules.keySet()));

    do {
      ImmutableSet toResolve =
          Sets.difference(
                  unresolvedModulesByClosureNamespace.keySet(), resolvedClosureModules.keySet())
              .immutableCopy();

      for (String namespace : toResolve) {
        resolvedClosureModules.put(
            namespace, unresolvedModulesByClosureNamespace.get(namespace).resolve(requestResolver));
      }
    } while (!resolvedClosureModules
        .keySet()
        .containsAll(unresolvedModulesByClosureNamespace.keySet()));

    unresolvedModules.clear();
    unresolvedModulesByClosureNamespace.clear();

    return new ModuleMap(
        ImmutableMap.copyOf(resolvedModules), ImmutableMap.copyOf(resolvedClosureModules));
  }

  private void process(ModuleMetadata moduleMetadata) {
    final ModuleProcessor processor;
    switch (moduleMetadata.moduleType()) {
      case ES6_MODULE:
        processor = esModuleProcessor;
        break;
      case GOOG_MODULE:
      case LEGACY_GOOG_MODULE:
        if (moduleMetadata.googNamespaces().size() == 1) {
          processor = closureModuleProcessor;
        } else {
          // this indicates some malformed Closure module. We should already have reported an
          // error.
          processor = nonEsModuleProcessor;
        }
        break;
      default:
        processor = nonEsModuleProcessor;
        break;
    }
    UnresolvedModule module =
        processor.process(moduleMetadata, moduleMetadata.path(), moduleMetadata.rootNode());

    // Have to use module names as keys because path "resolution" (ModuleLoader) "respects"
    // leading slashes. Meaning that if you look up "file.js" and "/file.js" you'll get
    // different paths back. But they'll have the same module name.
    if (moduleMetadata.path() != null) {
      unresolvedModules.put(moduleMetadata.path().toModuleName(), module);
    }

    for (String namespace : moduleMetadata.googNamespaces()) {
      unresolvedModulesByClosureNamespace.put(namespace, module);
    }
  }

  @Override
  public void process(Node externs, Node root) {
    compiler.setModuleMap(create());
  }

}