feat: introduce injectable filesystem context

.nx/version-plans/version-plan-1784629893636.md

@@ -0,0 +1,5 @@
+---
+__default__: minor
+---
+
+Add an injectable filesystem context and in-memory filesystem helper for hermetic Harness integrations and tests.

packages/github-action/eslint.config.mjs

@@ -2,6 +2,29 @@ import baseConfig from '../../eslint.config.mjs';
 
 export default [
   ...baseConfig,
+  {
+    files: ['src/shared/**/*.ts'],
+    ignores: ['src/shared/__tests__/**'],
+    rules: {
+      'no-restricted-imports': [
+        'error',
+        {
+          paths: [
+            {
+              name: 'node:fs',
+              message:
+                'Use getFs() from @react-native-harness/tools/harness-context instead.',
+            },
+            {
+              name: 'node:fs/promises',
+              message:
+                'Use getFs() from @react-native-harness/tools/harness-context instead.',
+            },
+          ],
+        },
+      ],
+    },
+  },
   {
     files: ['**/*.json'],
     rules: {

packages/github-action/package.json

@@ -13,7 +13,8 @@
   "dependencies": {
     "@react-native-harness/cache": "workspace:*",
     "@react-native-harness/config": "workspace:*",
-    "@react-native-harness/platform-android": "workspace:*"
+    "@react-native-harness/platform-android": "workspace:*",
+    "@react-native-harness/tools": "workspace:*"
   },
   "devDependencies": {
     "tsup": "^8.5.1"

packages/github-action/src/shared/__tests__/plan-restore.test.ts

@@ -1,7 +1,11 @@
-import fs from 'node:fs';
-import os from 'node:os';
 import path from 'node:path';
+import {
+  runWithHarnessContext,
+  type FileSystem,
+} from '@react-native-harness/tools/harness-context';
+import { createInMemoryFileSystem } from '@react-native-harness/tools/testing';
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { run } from '../plan-restore-run.js';
 
 const mocks = vi.hoisted(() => ({
   getConfig: vi.fn(),
@@ -23,16 +27,18 @@ vi.mock('@react-native-harness/cache', () => ({
 describe('plan-restore', () => {
   let projectRoot: string;
   let githubOutputPath: string;
+  let fileSystem: FileSystem;
   let planRestoreMock: ReturnType<typeof vi.fn>;
   let writeKeysFileMock: ReturnType<typeof vi.fn>;
 
   beforeEach(() => {
-    vi.resetModules();
     vi.clearAllMocks();
 
-    projectRoot = fs.mkdtempSync(path.join(os.tmpdir(), 'gha-plan-restore-'));
+    fileSystem = createInMemoryFileSystem();
+    projectRoot = '/project';
     githubOutputPath = path.join(projectRoot, 'github-output.txt');
-    fs.writeFileSync(githubOutputPath, '');
+    fileSystem.mkdirSync(projectRoot, { recursive: true });
+    fileSystem.writeFileSync(githubOutputPath, '');
 
     process.env.INPUT_PROJECTROOT = projectRoot;
     process.env.GITHUB_OUTPUT = githubOutputPath;
@@ -69,21 +75,20 @@ describe('plan-restore', () => {
   });
 
   afterEach(() => {
-    fs.rmSync(projectRoot, { recursive: true, force: true });
     delete process.env.INPUT_PROJECTROOT;
     delete process.env.GITHUB_OUTPUT;
     delete process.env.RUNNER_OS;
     vi.restoreAllMocks();
   });
 
   it('writes metroRestoreKey and metroRestorePrefixes (as JSON) to GITHUB_OUTPUT', async () => {
-    await import('../plan-restore.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(writeKeysFileMock).toHaveBeenCalled();
     });
 
-    const output = fs.readFileSync(githubOutputPath, 'utf8');
+    const output = fileSystem.readFileSync(githubOutputPath, 'utf8');
     expect(output).toContain('metroRestoreKey=harness-metro-linux-abc\n');
     expect(output).toContain(
       'metroRestorePrefixes=["harness-metro-linux-abc-"]\n'
@@ -94,7 +99,7 @@ describe('plan-restore', () => {
   });
 
   it('calls planRestore with the os and staticInputs assembled from the Metro key recipe', async () => {
-    await import('../plan-restore.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(planRestoreMock).toHaveBeenCalled();
@@ -111,7 +116,7 @@ describe('plan-restore', () => {
   it('fails loudly (process.exit(1)) when GITHUB_OUTPUT is not set', async () => {
     delete process.env.GITHUB_OUTPUT;
 
-    await import('../plan-restore.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(process.exit).toHaveBeenCalledWith(1);

packages/github-action/src/shared/__tests__/plan-save.test.ts

@@ -1,7 +1,11 @@
-import fs from 'node:fs';
-import os from 'node:os';
 import path from 'node:path';
+import {
+  runWithHarnessContext,
+  type FileSystem,
+} from '@react-native-harness/tools/harness-context';
+import { createInMemoryFileSystem } from '@react-native-harness/tools/testing';
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { run } from '../plan-save-run.js';
 
 const mocks = vi.hoisted(() => ({
   getConfig: vi.fn(),
@@ -21,16 +25,18 @@ vi.mock('@react-native-harness/cache', () => ({
 describe('plan-save', () => {
   let projectRoot: string;
   let githubOutputPath: string;
+  let fileSystem: FileSystem;
   let planSaveMock: ReturnType<typeof vi.fn>;
   let writeKeysFileMock: ReturnType<typeof vi.fn>;
 
   beforeEach(() => {
-    vi.resetModules();
     vi.clearAllMocks();
 
-    projectRoot = fs.mkdtempSync(path.join(os.tmpdir(), 'gha-plan-save-'));
+    fileSystem = createInMemoryFileSystem();
+    projectRoot = '/project';
     githubOutputPath = path.join(projectRoot, 'github-output.txt');
-    fs.writeFileSync(githubOutputPath, '');
+    fileSystem.mkdirSync(projectRoot, { recursive: true });
+    fileSystem.writeFileSync(githubOutputPath, '');
 
     process.env.INPUT_PROJECTROOT = projectRoot;
     process.env.GITHUB_OUTPUT = githubOutputPath;
@@ -69,7 +75,6 @@ describe('plan-save', () => {
   });
 
   afterEach(() => {
-    fs.rmSync(projectRoot, { recursive: true, force: true });
     delete process.env.INPUT_PROJECTROOT;
     delete process.env.GITHUB_OUTPUT;
     delete process.env.RUNNER_OS;
@@ -80,21 +85,21 @@ describe('plan-save', () => {
   });
 
   it('writes metroShouldSave and metroSaveKey to GITHUB_OUTPUT', async () => {
-    await import('../plan-save.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(writeKeysFileMock).toHaveBeenCalled();
     });
 
-    const output = fs.readFileSync(githubOutputPath, 'utf8');
+    const output = fileSystem.readFileSync(githubOutputPath, 'utf8');
     expect(output).toContain('metroShouldSave=true\n');
     expect(output).toContain(
       'metroSaveKey=harness-metro-linux-abc-contenthash\n'
     );
   });
 
   it('parses the metroSnapshot input and builds the SavePolicy from env/input', async () => {
-    await import('../plan-save.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(planSaveMock).toHaveBeenCalled();
@@ -110,7 +115,7 @@ describe('plan-save', () => {
   it('treats an unparseable metroSnapshot input as an empty snapshot instead of throwing', async () => {
     process.env.INPUT_METRO_SNAPSHOT = 'not json';
 
-    await import('../plan-save.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(planSaveMock).toHaveBeenCalled();
@@ -127,7 +132,7 @@ describe('plan-save', () => {
   it('defaults an unrecognized cacheSavePolicy input to "default-branch"', async () => {
     process.env.INPUT_CACHESAVEPOLICY = 'bogus';
 
-    await import('../plan-save.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(planSaveMock).toHaveBeenCalled();
@@ -156,7 +161,7 @@ describe('plan-save', () => {
       },
     });
 
-    await import('../plan-save.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(writeKeysFileMock).toHaveBeenCalled();
@@ -179,7 +184,7 @@ describe('plan-save', () => {
       },
     });
 
-    await import('../plan-save.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(writeKeysFileMock).toHaveBeenCalled();
@@ -203,7 +208,7 @@ describe('plan-save', () => {
       },
     });
 
-    await import('../plan-save.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(writeKeysFileMock).toHaveBeenCalled();
@@ -227,7 +232,7 @@ describe('plan-save', () => {
       },
     });
 
-    await import('../plan-save.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(writeKeysFileMock).toHaveBeenCalled();
@@ -241,7 +246,7 @@ describe('plan-save', () => {
   it('fails loudly (process.exit(1)) when GITHUB_OUTPUT is not set', async () => {
     delete process.env.GITHUB_OUTPUT;
 
-    await import('../plan-save.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(process.exit).toHaveBeenCalledWith(1);

packages/github-action/src/shared/__tests__/snapshot-metro.test.ts

@@ -1,7 +1,11 @@
-import fs from 'node:fs';
-import os from 'node:os';
 import path from 'node:path';
+import {
+  runWithHarnessContext,
+  type FileSystem,
+} from '@react-native-harness/tools/harness-context';
+import { createInMemoryFileSystem } from '@react-native-harness/tools/testing';
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { run } from '../snapshot-metro-run.js';
 
 const mocks = vi.hoisted(() => ({
   getConfig: vi.fn(),
@@ -19,15 +23,17 @@ vi.mock('@react-native-harness/cache', () => ({
 describe('snapshot-metro', () => {
   let projectRoot: string;
   let githubOutputPath: string;
+  let fileSystem: FileSystem;
   let snapshotMock: ReturnType<typeof vi.fn>;
 
   beforeEach(() => {
-    vi.resetModules();
     vi.clearAllMocks();
 
-    projectRoot = fs.mkdtempSync(path.join(os.tmpdir(), 'gha-snapshot-metro-'));
+    fileSystem = createInMemoryFileSystem();
+    projectRoot = '/project';
     githubOutputPath = path.join(projectRoot, 'github-output.txt');
-    fs.writeFileSync(githubOutputPath, '');
+    fileSystem.mkdirSync(projectRoot, { recursive: true });
+    fileSystem.writeFileSync(githubOutputPath, '');
 
     process.env.INPUT_PROJECTROOT = projectRoot;
     process.env.GITHUB_OUTPUT = githubOutputPath;
@@ -51,21 +57,20 @@ describe('snapshot-metro', () => {
   });
 
   afterEach(() => {
-    fs.rmSync(projectRoot, { recursive: true, force: true });
     delete process.env.INPUT_PROJECTROOT;
     delete process.env.GITHUB_OUTPUT;
     delete process.env.METRO_RESTORED_KEY;
     vi.restoreAllMocks();
   });
 
   it('writes the current cache snapshot to GITHUB_OUTPUT as metroSnapshot', async () => {
-    await import('../snapshot-metro.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(snapshotMock).toHaveBeenCalled();
     });
 
-    const output = fs.readFileSync(githubOutputPath, 'utf8');
+    const output = fileSystem.readFileSync(githubOutputPath, 'utf8');
     expect(output).toContain(
       'metroSnapshot={"metro":[{"path":"metro/a","sizeBytes":3,"mtimeMs":1}]}\n'
     );
@@ -80,7 +85,7 @@ describe('snapshot-metro', () => {
       ],
     });
 
-    await import('../snapshot-metro.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(snapshotMock).toHaveBeenCalled();
@@ -94,7 +99,7 @@ describe('snapshot-metro', () => {
   it('reports a cold start when no cache entry matched', async () => {
     delete process.env.METRO_RESTORED_KEY;
 
-    await import('../snapshot-metro.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(snapshotMock).toHaveBeenCalled();
@@ -108,7 +113,7 @@ describe('snapshot-metro', () => {
   it('fails loudly (process.exit(1)) when GITHUB_OUTPUT is not set', async () => {
     delete process.env.GITHUB_OUTPUT;
 
-    await import('../snapshot-metro.js');
+    await runWithHarnessContext({ fs: fileSystem }, run);
 
     await vi.waitFor(() => {
       expect(process.exit).toHaveBeenCalledWith(1);

packages/github-action/src/shared/index.ts

@@ -3,8 +3,12 @@ import {
   getEmulatorCpuCores,
   getHostAndroidSystemImageArch,
 } from '@react-native-harness/platform-android';
+import {
+  getFs,
+  getHarnessContext,
+  runWithHarnessContext,
+} from '@react-native-harness/tools/harness-context';
 import path from 'node:path';
-import fs from 'node:fs';
 
 const resolveAvdCachingEnabled = ({
   snapshotEnabled,
@@ -122,7 +126,7 @@ const run = async (): Promise<void> => {
     const output = `config=${JSON.stringify(
       resolvedRunner
     )}\nprojectRoot=${relativeProjectRoot}\n`;
-    fs.appendFileSync(githubOutput, output);
+    getFs().appendFileSync(githubOutput, output);
   } catch (error) {
     if (error instanceof Error) {
       console.error(error.message);
@@ -134,4 +138,4 @@ const run = async (): Promise<void> => {
   }
 };
 
-run();
+runWithHarnessContext(getHarnessContext(), run);

packages/github-action/src/shared/metro-cache-inputs.ts

@@ -1,6 +1,6 @@
-import fs from 'node:fs';
 import path from 'node:path';
 import { computeMetroStaticInputs } from '@react-native-harness/cache';
+import { getFs } from '@react-native-harness/tools/harness-context';
 
 const FALLBACK_BUNDLER_METRO_VERSION = 'unknown';
 
@@ -16,7 +16,7 @@ export const resolveRepoRoot = (projectRoot: string): string => {
   let dir = projectRoot;
 
   while (true) {
-    if (fs.existsSync(path.join(dir, '.git'))) {
+    if (getFs().existsSync(path.join(dir, '.git'))) {
       return dir;
     }
 
@@ -65,7 +65,9 @@ const resolveBundlerMetroPackageJson = (projectRoot: string): string => {
 export const resolveBundlerMetroVersion = (projectRoot: string): string => {
   try {
     const packageJsonPath = resolveBundlerMetroPackageJson(projectRoot);
-    const packageJson = JSON.parse(fs.readFileSync(packageJsonPath, 'utf8'));
+    const packageJson = JSON.parse(
+      getFs().readFileSync(packageJsonPath, 'utf8')
+    );
 
     if (typeof packageJson.version !== 'string') {
       throw new Error('"version" field is missing or not a string');