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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.modules;

import static com.google.common.base.Preconditions.checkArgument;

import com.google.auto.value.AutoValue;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.javascript.jscomp.NodeUtil;
import com.google.javascript.jscomp.modules.Binding.CreatedBy;
import com.google.javascript.rhino.Node;
import org.jspecify.nullness.Nullable;

/**
 * Handles creating an {@link Import} from goog.require(Type) or goog.forwardDeclare.
 *
 * This logic can be used by both goog.modules and ES modules
 */
final class ClosureRequireProcessor {
  private final Node nameDeclaration;
  private final CreatedBy requireKind;

  /** Represents a goog.require(Type) or goog.forwardDeclare */
  @AutoValue
  abstract static class Require {
    /** The name local to the module with the require; e.g. `b` in `const b = goog.require('a');` */
    abstract String localName();
    /** An {@link Import} containing all metadata about this require */
    abstract Import importRecord();
    /** Whether this is a goog.require, goog.requireType, or goog.forwardDeclare */
    abstract CreatedBy createdBy();

    private static Require create(String localName, Import importRecord, CreatedBy createdBy) {
      checkArgument(createdBy.isClosureImport());
      return new AutoValue_ClosureRequireProcessor_Require(localName, importRecord, createdBy);
    }
  }

  private ClosureRequireProcessor(Node nameDeclaration, CreatedBy requireKind) {
    checkArgument(NodeUtil.isNameDeclaration(nameDeclaration));
    this.nameDeclaration = nameDeclaration;
    this.requireKind = requireKind;
  }

  /**
   * Returns all Require built from the given statement, or null if it is not a require
   *
   * @param nameDeclaration a VAR, LET, or CONST
   * @return all Requires contained in this declaration
   */
  static ImmutableList getAllRequires(Node nameDeclaration) {
    Node rhs =
        nameDeclaration.getFirstChild().isDestructuringLhs()
            ? nameDeclaration.getFirstChild().getSecondChild()
            : nameDeclaration.getFirstFirstChild();
    // This may be a require, requireType, or forwardDeclare.
    CreatedBy requireKind = getModuleDependencyTypeFromRhs(rhs);
    if (requireKind == null) {
      return ImmutableList.of();
    }

    return new ClosureRequireProcessor(nameDeclaration, requireKind).getAllRequiresInDeclaration();
  }

  private static final ImmutableMap GOOG_DEPENDENCY_CALLS =
      ImmutableMap.of(
          "require",
          CreatedBy.GOOG_REQUIRE,
          "requireType",
          CreatedBy.GOOG_REQUIRE_TYPE,
          "forwardDeclare",
          CreatedBy.GOOG_FORWARD_DECLARE);

  /**
   * Checks if the given rvalue is a goog.require(Type) or goog.forwardDeclare call, and if so
   * returns which one.
   *
   * @return A Closure require (where {@link CreatedBy#isClosureImport()} is true) or null.
   */
  private static @Nullable CreatedBy getModuleDependencyTypeFromRhs(@Nullable Node value) {
    if (value == null
        || !value.isCall()
        || !value.hasTwoChildren()
        || !value.getSecondChild().isStringLit()) {
      return null;
    }
    Node callee = value.getFirstChild();
    if (!callee.isGetProp()) {
      return null;
    }
    Node owner = callee.getFirstChild();
    if (!owner.isName() || !owner.getString().equals("goog")) {
      return null;
    }
    return GOOG_DEPENDENCY_CALLS.get(callee.getString());
  }

  /** Returns a new list of all required names in {@link #nameDeclaration} */
  private ImmutableList getAllRequiresInDeclaration() {
    Node rhs =
        nameDeclaration.getFirstChild().isDestructuringLhs()
            ? nameDeclaration.getFirstChild().getSecondChild()
            : nameDeclaration.getFirstFirstChild();

    String namespace = rhs.getSecondChild().getString();

    if (nameDeclaration.getFirstChild().isName()) {
      // const modA = goog.require('modA');
      Node lhs = nameDeclaration.getFirstChild();
      return ImmutableList.of(
          Require.create(
              lhs.getString(),
              Import.builder()
                  .moduleRequest(namespace)
                  .localName(lhs.getString())
                  .importName(Export.NAMESPACE)
                  .importNode(nameDeclaration)
                  .nameNode(lhs)
                  .build(),
              requireKind));
    } else {
      // const {x, y} = goog.require('modA');
      Node objectPattern = nameDeclaration.getFirstFirstChild();
      if (!objectPattern.isObjectPattern()) {
        // bad JS, ignore
        return ImmutableList.of();
      }
      return getAllRequiresFromDestructuring(objectPattern, namespace);
    }
  }

  /** Returns all requires from destructruring, like `const {x, y, z} = goog.require('a');` */
  private ImmutableList getAllRequiresFromDestructuring(
      Node objectPattern, String namespace) {
    ImmutableList.Builder requireBuilder = ImmutableList.builder();
    for (Node key = objectPattern.getFirstChild(); key != null; key = key.getNext()) {
      if (!key.isStringKey()) {
        // Bad code, just ignore. We warn elsewhere.
        continue;
      }
      Node lhs = key.getOnlyChild();
      if (!lhs.isName()) {
        // Bad code ( e.g. `const {a = 0} = goog.require(...)`). We warn elsewhere.
        continue;
      }

      requireBuilder.add(
          Require.create(
              lhs.getString(),
              Import.builder()
                  .moduleRequest(namespace)
                  .localName(lhs.getString())
                  .importName(key.getString())
                  .importNode(nameDeclaration)
                  .nameNode(lhs)
                  .build(),
              requireKind));
    }
    return requireBuilder.build();
  }
}