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feat(metro-file-map): Lazily stat files and populate symlinks for Node crawled file trees #1686

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0fd5007
Avoid stat when file is new/unaccessed
kitten Apr 10, 2026
5fae6ef
Add new test cases
kitten Apr 10, 2026
34e30b4
Lazily populate cold startup symlinks
kitten Apr 10, 2026
6d1b062
Add new test cases #2
kitten Apr 10, 2026
3c2d74c
Rebuild ts-defs
kitten Apr 11, 2026
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57 changes: 57 additions & 0 deletions packages/metro-file-map/src/__tests__/index-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -176,6 +176,19 @@ jest.mock('fs', () => ({
error.code = 'ENOENT';
throw error;
}),
readlinkSync: jest.fn(path => {
const entry = mockFs[path];
if (!entry) {
const error = new Error(`Cannot read path '${path}'.`);
// $FlowFixMe[prop-missing] code
error.code = 'ENOENT';
throw error;
}
if (typeof entry.link !== 'string') {
throw new Error(`Not a symlink: '${path}'.`);
}
return entry.link;
}),
writeFileSync: jest.fn((path, data, options) => {
expect(options).toBe(require('v8').serialize ? undefined : 'utf8');
mockFs[path] = data;
Expand Down Expand Up @@ -749,6 +762,50 @@ describe('FileMap', () => {
);
});

test('defers symlink resolution for entries with null mtime', async () => {
const node = require('../crawlers/node').default;
const fsModule = require('fs');

// $FlowFixMe[prop-missing]
// $FlowFixMe[missing-local-annot]
node.mockImplementation(options => {
const changedFiles = createMap<FileMetadata>({
[path.join('fruits', 'Strawberry.js')]: [32, 42, 0, null, 0, null],
[path.join('fruits', 'LinkToStrawberry.js')]: [
null,
0,
0,
null,
1,
null,
],
});
return Promise.resolve({changedFiles, removedFiles: new Set()});
});

const {fileSystem} = await buildNewFileMap({
enableSymlinks: true,
useWatchman: false,
});

expect(fsModule.promises.readlink).not.toHaveBeenCalledWith(
expect.stringContaining('LinkToStrawberry'),
);

expect(
fileSystem.lookup(
path.join('/', 'project', 'fruits', 'LinkToStrawberry.js'),
),
).toMatchObject({
exists: true,
realPath: path.join('/', 'project', 'fruits', 'Strawberry.js'),
});

expect(fsModule.readlinkSync).toHaveBeenCalledWith(
path.join('/', 'project', 'fruits', 'LinkToStrawberry.js'),
);
});

test('handles a Haste module moving between builds', async () => {
mockFs = object({
[path.join('/', 'project', 'vegetables', 'Melon.js')]: `
Expand Down
73 changes: 42 additions & 31 deletions packages/metro-file-map/src/crawlers/__tests__/integration-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -80,44 +80,55 @@ function oneOf(this: $FlowFixMe, actual: unknown, ...expectOneOf: unknown[]) {
* https://fburl.com/gdoc/y8dn025u */
expect.extend({oneOf});

const CASES = [
[
true,
new Map([
['foo.js', [expect.any(Number), 245, 0, null, 0, null]],
[
join('directory', 'bar.js'),
[expect.any(Number), 245, 0, null, 0, null],
],
[
'link-to-directory',
[expect.any(Number), 9, 0, null, expect.oneOf(1, 'directory'), null],
],
[
'link-to-foo.js',
[expect.any(Number), 6, 0, null, expect.oneOf(1, 'foo.js'), null],
],
]),
],
[
false,
new Map([
[
join('directory', 'bar.js'),
[expect.any(Number), 245, 0, null, 0, null],
],
['foo.js', [expect.any(Number), 245, 0, null, 0, null]],
]),
],
];
function getCases(skipsStat: boolean) {
const fileEntry = skipsStat
? [null, 0, 0, null, 0, null]
: [expect.any(Number), 245, 0, null, 0, null];
return [
[
true,
new Map([
['foo.js', fileEntry],
[join('directory', 'bar.js'), fileEntry],
[
'link-to-directory',
skipsStat
? [null, 0, 0, null, 1, null]
: [
expect.any(Number),
9,
0,
null,
expect.oneOf(1, 'directory'),
null,
],
],
[
'link-to-foo.js',
skipsStat
? [null, 0, 0, null, 1, null]
: [expect.any(Number), 6, 0, null, expect.oneOf(1, 'foo.js'), null],
],
]),
],
[
false,
new Map([
[join('directory', 'bar.js'), fileEntry],
['foo.js', fileEntry],
]),
],
];
}

describe.each(Object.keys(CRAWLERS))(
'Crawler integration tests (%s)',
crawlerName => {
const crawl = CRAWLERS[crawlerName];
const maybeTest = crawl ? test : test.skip;
const skipsStat = crawlerName === 'node-recursive';

maybeTest.each(CASES)(
maybeTest.each(getCases(skipsStat))(
'Finds the expected files (includeSymlinks: %s)',
async (includeSymlinks, expectedChangedFiles) => {
invariant(crawl, 'crawl should not be null within maybeTest');
Expand Down
118 changes: 108 additions & 10 deletions packages/metro-file-map/src/crawlers/__tests__/node-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -272,8 +272,8 @@ describe('node crawler', () => {
);
expect(changedFiles).toEqual(
createMap({
'fruits/directory/strawberry.js': [33, 42, 0, null, 0, null],
'fruits/tomato.js': [32, 42, 0, null, 0, null],
'fruits/directory/strawberry.js': [null, 0, 0, null, 0, null],
'fruits/tomato.js': [null, 0, 0, null, 0, null],
}),
);
expect(removedFiles).toEqual(new Set());
Expand All @@ -297,8 +297,8 @@ describe('node crawler', () => {

expect(changedFiles).toEqual(
createMap({
'fruits/directory/strawberry.js': [33, 42, 0, null, 0, null],
'fruits/tomato.js': [32, 42, 0, null, 0, null],
'fruits/directory/strawberry.js': [null, 0, 0, null, 0, null],
'fruits/tomato.js': [null, 0, 0, null, 0, null],
}),
);
expect(removedFiles).toEqual(new Set());
Expand All @@ -321,8 +321,8 @@ describe('node crawler', () => {
expect(childProcess.spawn).toHaveBeenCalledTimes(0);
expect(changedFiles).toEqual(
createMap({
'fruits/directory/strawberry.js': [33, 42, 0, null, 0, null],
'fruits/tomato.js': [32, 42, 0, null, 0, null],
'fruits/directory/strawberry.js': [null, 0, 0, null, 0, null],
'fruits/tomato.js': [null, 0, 0, null, 0, null],
}),
);
expect(removedFiles).toEqual(new Set());
Expand Down Expand Up @@ -386,17 +386,115 @@ describe('node crawler', () => {

expect(changedFiles).toEqual(
createMap({
'fruits/directory/strawberry.js': [33, 42, 0, null, 0, null],
'fruits/tomato.js': [32, 42, 0, null, 0, null],
'fruits/directory/strawberry.js': [null, 0, 0, null, 0, null],
'fruits/tomato.js': [null, 0, 0, null, 0, null],
}),
);
expect(removedFiles).toEqual(new Set());
// once for /project/fruits, once for /project/fruits/directory
expect(fs.readdir).toHaveBeenCalledTimes(2);
// once for strawberry.js, once for tomato.js
expect(fs.lstat).toHaveBeenCalledTimes(0);
});

test('skips lstat for files with no prior mtime', async () => {
nodeCrawl = require('../node').default;
const fs = require('graceful-fs');

const files = createMap({
'fruits/tomato.js': [null, 0, 0, null, 0, null],
'fruits/directory/strawberry.js': [null, 0, 0, null, 0, null],
});

const {changedFiles, removedFiles} = await nodeCrawl({
console: global.console,
previousState: {fileSystem: getFS(files)},
extensions: ['js'],
forceNodeFilesystemAPI: true,
ignore: pearMatcher,
rootDir,
roots: ['/project/fruits'],
});

expect(changedFiles).toEqual(new Map());
expect(removedFiles).toEqual(new Set());
expect(fs.lstat).toHaveBeenCalledTimes(0);
});

test('calls lstat only for files with existing mtime', async () => {
nodeCrawl = require('../node').default;
const fs = require('graceful-fs');

const files = createMap({
'fruits/tomato.js': [31, 42, 1, null, 0, null],
'fruits/directory/strawberry.js': [null, 0, 0, null, 0, null],
});

const {changedFiles, removedFiles} = await nodeCrawl({
console: global.console,
previousState: {fileSystem: getFS(files)},
extensions: ['js'],
forceNodeFilesystemAPI: true,
ignore: pearMatcher,
rootDir,
roots: ['/project/fruits'],
});

expect(changedFiles).toEqual(
createMap({
'fruits/tomato.js': [32, 42, 0, null, 0, null],
}),
);
expect(removedFiles).toEqual(new Set());
expect(fs.lstat).toHaveBeenCalledTimes(1);
});

test('excludes unchanged files when lstat mtime matches cache', async () => {
nodeCrawl = require('../node').default;
const fs = require('graceful-fs');

const files = createMap({
'fruits/tomato.js': [32, 42, 1, null, 0, null],
'fruits/directory/strawberry.js': [33, 42, 1, null, 0, null],
});

const {changedFiles, removedFiles} = await nodeCrawl({
console: global.console,
previousState: {fileSystem: getFS(files)},
extensions: ['js'],
forceNodeFilesystemAPI: true,
ignore: pearMatcher,
rootDir,
roots: ['/project/fruits'],
});

expect(changedFiles).toEqual(new Map());
expect(removedFiles).toEqual(new Set());
expect(fs.lstat).toHaveBeenCalledTimes(2);
});

test('marks symlinks correctly when stat is skipped', async () => {
nodeCrawl = require('../node').default;

const {changedFiles} = await nodeCrawl({
console: global.console,
previousState: {fileSystem: emptyFS},
extensions: ['js'],
forceNodeFilesystemAPI: true,
includeSymlinks: true,
ignore: pearMatcher,
rootDir,
roots: ['/project/fruits'],
});

expect(changedFiles.get(normalize('fruits/symlink'))).toEqual([
null,
0,
0,
null,
1,
null,
]);
});

test('aborts the crawl on pre-aborted signal', async () => {
nodeCrawl = require('../node').default;
const err = new Error('aborted for test');
Expand Down
43 changes: 28 additions & 15 deletions packages/metro-file-map/src/crawlers/node/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@ import type {
CrawlerOptions,
CrawlResult,
FileData,
FileSystem,
IgnoreMatcher,
} from '../../flow-types';

Expand All @@ -36,6 +37,7 @@ function find(
includeSymlinks: boolean,
rootDir: string,
console: Console,
previousFileSystem: FileSystem | null,
callback: Callback,
): void {
const result: FileData = new Map();
Expand All @@ -58,7 +60,8 @@ function find(
return;
}

if (entry.isSymbolicLink() && !includeSymlinks) {
const isSymlink = entry.isSymbolicLink();
if (isSymlink && !includeSymlinks) {
return;
}

Expand All @@ -67,29 +70,38 @@ function find(
return;
}

activeCalls++;

fs.lstat(file, (err, stat) => {
activeCalls--;
const ext = path.extname(file).substr(1);
if (!isSymlink && !extensions.includes(ext)) {
return;
}

if (!err && stat) {
const ext = path.extname(file).substr(1);
if (stat.isSymbolicLink() || extensions.includes(ext)) {
result.set(pathUtils.absoluteToNormal(file), [
const fileNormal = pathUtils.absoluteToNormal(file);
const mtime = previousFileSystem?.getMtimeByNormalPath(fileNormal);
if (mtime == null || mtime === 0) {
// When we're in a cold start or a previous file doesn't exist, we can skip
// the mtime/size lstat now and treat the file as new
result.set(fileNormal, [null, 0, 0, null, isSymlink ? 1 : 0, null]);
} else {
activeCalls++;
fs.lstat(file, (err, stat) => {
activeCalls--;

if (!err && stat) {
result.set(fileNormal, [
stat.mtime.getTime(),
stat.size,
0,
null,
stat.isSymbolicLink() ? 1 : 0,
isSymlink ? 1 : 0,
null,
]);
}
}

if (activeCalls === 0) {
callback(result);
}
});
if (activeCalls === 0) {
callback(result);
}
});
}
});
}

Expand Down Expand Up @@ -232,6 +244,7 @@ export default async function nodeCrawl(
includeSymlinks,
rootDir,
console,
previousState.fileSystem,
callback,
);
}
Expand Down
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