refactor(compiler-cli): support Buffer files in `FileSystem` (#36843)

Adding `readFileBuffer()` method and allowing `writeFile()` to accept a
Buffer object will be useful when reading and writing non-text files,
such as is done in the `@angular/localize` package.

PR Close #36843

packages/compiler-cli/src/ngtsc/file_system/src/invalid_file_system.ts

@@ -22,7 +22,10 @@ export class InvalidFileSystem implements FileSystem {
   readFile(path: AbsoluteFsPath): string {
     throw makeError();
   }
-  writeFile(path: AbsoluteFsPath, data: string, exclusive?: boolean): void {
+  readFileBuffer(path: AbsoluteFsPath): Buffer {
+    throw makeError();
+  }
+  writeFile(path: AbsoluteFsPath, data: string|Buffer, exclusive?: boolean): void {
     throw makeError();
   }
   removeFile(path: AbsoluteFsPath): void {

packages/compiler-cli/src/ngtsc/file_system/src/node_js_file_system.ts

@@ -23,7 +23,10 @@ export class NodeJSFileSystem implements FileSystem {
   readFile(path: AbsoluteFsPath): string {
     return fs.readFileSync(path, 'utf8');
   }
-  writeFile(path: AbsoluteFsPath, data: string, exclusive: boolean = false): void {
+  readFileBuffer(path: AbsoluteFsPath): Buffer {
+    return fs.readFileSync(path);
+  }
+  writeFile(path: AbsoluteFsPath, data: string|Buffer, exclusive: boolean = false): void {
     fs.writeFileSync(path, data, exclusive ? {flag: 'wx'} : undefined);
   }
   removeFile(path: AbsoluteFsPath): void {

packages/compiler-cli/src/ngtsc/file_system/src/types.ts

@@ -37,7 +37,8 @@ export type PathSegment = BrandedPath<'PathSegment'>;
 export interface FileSystem {
   exists(path: AbsoluteFsPath): boolean;
   readFile(path: AbsoluteFsPath): string;
-  writeFile(path: AbsoluteFsPath, data: string, exclusive?: boolean): void;
+  readFileBuffer(path: AbsoluteFsPath): Buffer;
+  writeFile(path: AbsoluteFsPath, data: string|Buffer, exclusive?: boolean): void;
   removeFile(path: AbsoluteFsPath): void;
   symlink(target: AbsoluteFsPath, path: AbsoluteFsPath): void;
   readdir(path: AbsoluteFsPath): PathSegment[];

packages/compiler-cli/src/ngtsc/file_system/test/node_js_file_system_spec.ts

@@ -44,6 +44,16 @@ describe('NodeJSFileSystem', () => {
     });
   });
 
+  describe('readFileBuffer()', () => {
+    it('should delegate to fs.readFileSync()', () => {
+      const buffer = new Buffer('Some contents');
+      const spy = spyOn(realFs, 'readFileSync').and.returnValue(buffer);
+      const result = fs.readFileBuffer(abcPath);
+      expect(result).toBe(buffer);
+      expect(spy).toHaveBeenCalledWith(abcPath);
+    });
+  });
+
   describe('writeFile()', () => {
     it('should delegate to fs.writeFileSync()', () => {
       const spy = spyOn(realFs, 'writeFileSync');

packages/compiler-cli/src/ngtsc/file_system/testing/src/mock_file_system.ts

@@ -32,13 +32,22 @@ export abstract class MockFileSystem implements FileSystem {
   readFile(path: AbsoluteFsPath): string {
     const {entity} = this.findFromPath(path);
     if (isFile(entity)) {
-      return entity;
+      return entity.toString();
     } else {
       throw new MockFileSystemError('ENOENT', path, `File "${path}" does not exist.`);
     }
   }
 
-  writeFile(path: AbsoluteFsPath, data: string, exclusive: boolean = false): void {
+  readFileBuffer(path: AbsoluteFsPath): Buffer {
+    const {entity} = this.findFromPath(path);
+    if (isFile(entity)) {
+      return Buffer.isBuffer(entity) ? entity : new Buffer(entity);
+    } else {
+      throw new MockFileSystemError('ENOENT', path, `File "${path}" does not exist.`);
+    }
+  }
+
+  writeFile(path: AbsoluteFsPath, data: string|Buffer, exclusive: boolean = false): void {
     const [folderPath, basename] = this.splitIntoFolderAndFile(path);
     const {entity} = this.findFromPath(folderPath);
     if (entity === null || !isFolder(entity)) {
@@ -286,7 +295,7 @@ export type Entity = Folder|File|SymLink;
 export interface Folder {
   [pathSegments: string]: Entity;
 }
-export type File = string;
+export type File = string|Buffer;
 export class SymLink {
   constructor(public path: AbsoluteFsPath) {}
 }
@@ -311,7 +320,7 @@ class MockFileSystemError extends Error {
 }
 
 export function isFile(item: Entity|null): item is File {
-  return typeof item === 'string';
+  return Buffer.isBuffer(item) || typeof item === 'string';
 }
 
 export function isSymLink(item: Entity|null): item is SymLink {