angular-docs-cn/packages/compiler-cli/linker/src/linker_import_generator.ts

/**
 * @license
 * Copyright Google LLC All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */
import {ImportGenerator, NamedImport} from '../../src/ngtsc/translator';
import {FatalLinkerError} from './fatal_linker_error';

/**
 * A class that is used to generate imports when translating from Angular Output AST to an AST to
 * render, such as Babel.
 *
 * Note that, in the linker, there can only be imports from `@angular/core` and that these imports
 * must be achieved by property access on an `ng` namespace identifer, which is passed in via the
 * constructor.
 */
export class LinkerImportGenerator<TExpression> implements ImportGenerator<TExpression> {
  constructor(private ngImport: TExpression) {}

  generateNamespaceImport(moduleName: string): TExpression {
    this.assertModuleName(moduleName);
    return this.ngImport;
  }

  generateNamedImport(moduleName: string, originalSymbol: string): NamedImport<TExpression> {
    this.assertModuleName(moduleName);
    return {moduleImport: this.ngImport, symbol: originalSymbol};
  }

  private assertModuleName(moduleName: string): void {
    if (moduleName !== '@angular/core') {
      throw new FatalLinkerError(
          this.ngImport, `Unable to import from anything other than '@angular/core'`);
    }
  }
}