perf(ivy): ngcc - add a cache to the FileSystem (#30525)

When profiling ngcc it is notable that a large amount of time
is spent dealing with an exception that is thrown (and handled
internally by fs) when checking the existence of a file.

We check file existence a lot in both finding entry-points
and when TS is compiling code. This commit adds a simple
cached `FileSystem`, which wraps a real `FileSystem` delegate.
This will reduce the number of calls through to `fs.exists()` and
`fs.readFile()` on the delegate.

Initial benchmarks indicate that the cache is miss to hit ratio
for `exists()` is about 2:1, which means that we save about 1/3
of the calls to `fs.existsSync()`.

Note that this implements a "non-expiring" cache, so it is not suitable
for a long lived `FileSystem`, where files may be modified externally.
The cache will be updated if a file is changed or moved via
calls to `FileSystem` methods but it will not be aware of changes
to the files system from outside the `FileSystem` service.

For ngcc we must create a new `FileSystem` service
for each run of `mainNgcc` and ensure that all file operations
(including TS compilation) use the `FileSystem` service.
This ensures that it is very unlikely that a file will change
externally during `mainNgcc` processing.

PR Close #30525

packages/compiler-cli/ngcc/index.ts

@@ -5,20 +5,25 @@
  * 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 {CachedFileSystem, NodeJSFileSystem, setFileSystem} from '../src/ngtsc/file_system';
 
-import {NodeJSFileSystem, setFileSystem} from '../src/ngtsc/file_system';
+import {mainNgcc} from './src/main';
 import {hasBeenProcessed as _hasBeenProcessed} from './src/packages/build_marker';
 import {EntryPointJsonProperty, EntryPointPackageJson} from './src/packages/entry_point';
 
 export {ConsoleLogger, LogLevel} from './src/logging/console_logger';
 export {Logger} from './src/logging/logger';
-export {NgccOptions, mainNgcc as process} from './src/main';
+export {NgccOptions} from './src/main';
 export {PathMappings} from './src/utils';
 
 export function hasBeenProcessed(packageJson: object, format: string) {
-  // We are wrapping this function to hide the internal types.
+  // Recreate the file system on each call to reset the cache
+  setFileSystem(new CachedFileSystem(new NodeJSFileSystem()));
   return _hasBeenProcessed(packageJson as EntryPointPackageJson, format as EntryPointJsonProperty);
 }
 
-// Configure the file-system for external users.
-setFileSystem(new NodeJSFileSystem());
+export function process(...args: Parameters<typeof mainNgcc>) {
+  // Recreate the file system on each call to reset the cache
+  setFileSystem(new CachedFileSystem(new NodeJSFileSystem()));
+  return mainNgcc(...args);
+}

packages/compiler-cli/ngcc/main-ngcc.ts

@@ -8,7 +8,7 @@
  */
 import * as yargs from 'yargs';
 
-import {resolve, setFileSystem, NodeJSFileSystem} from '../src/ngtsc/file_system';
+import {resolve, setFileSystem, CachedFileSystem, NodeJSFileSystem} from '../src/ngtsc/file_system';
 import {mainNgcc} from './src/main';
 import {ConsoleLogger, LogLevel} from './src/logging/console_logger';
 
@@ -57,7 +57,7 @@ if (require.main === module) {
     process.exit(1);
   }
 
-  setFileSystem(new NodeJSFileSystem());
+  setFileSystem(new CachedFileSystem(new NodeJSFileSystem()));
 
   const baseSourcePath = resolve(options['s'] || './node_modules');
   const propertiesToConsider: string[] = options['p'];