Doist
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diff --git a/‎src/index.integration.test.mts‎
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@@ -6,7 +6,7 @@
 
 The [React Compiler](https://react.dev/learn/react-compiler) automatically memoizes your components, eliminating the need for `useCallback` and `useMemo`. However, certain code patterns cause the compiler to bail out. When this happens, your components lose automatic optimization, potentially causing performance regressions.
 
-Inspired by [esplint](https://github.com/hjylewis/esplint) and [react-compiler-marker](https://github.com/blazejkustra/react-compiler-marker), this tool tracks compiler errors in a `.react-compiler-tracker.json` file and integrates with Git hooks and CI to prevent new violations from being introduced.
+Inspired by [esplint](https://github.com/hjylewis/esplint) and [react-compiler-marker](https://github.com/blazejkustra/react-compiler-marker), this tool tracks compiler errors in a `.react-compiler.rec.json` file and integrates with Git hooks and CI to prevent new violations from being introduced.
 
 ## Prerequisites
 
@@ -22,24 +22,66 @@ npm install --save-dev babel-plugin-react-compiler
 npm install --save-dev @doist/react-compiler-tracker
 ```
 
+## Configuration
+
+Create a `.react-compiler-tracker.config.json` file in your project root to customize the tool's behavior:
+
+```json
+{
+    "recordsFile": ".react-compiler.rec.json",
+    "sourceGlob": "src/**/*.{js,jsx,ts,tsx}"
+}
+```
+
+All fields are optional. Default values are shown above.
+
+| Option | Description | Default |
+|--------|-------------|---------|
+| `recordsFile` | Path to the records file | `.react-compiler.rec.json` |
+| `sourceGlob` | Glob pattern for source files | `src/**/*.{js,jsx,ts,tsx}` |
+
+### Monorepo Usage
+
+In a monorepo, run the tool from your package directory. The config file and all paths are relative to where you run the command. The defaults typically work out of the box:
+
+```
+my-monorepo/
+├── packages/
+│   └── frontend/
+│       ├── .react-compiler-tracker.config.json  # Optional config
+│       ├── .react-compiler.rec.json             # Records file
+│       └── src/
+│           └── ...
+```
+
+If your source files are in a different location (e.g., `app/` instead of `src/`), customize the config:
+
+```json
+{
+    "sourceGlob": "app/**/*.{ts,tsx}"
+}
+```
+
 ## Usage
 
 ### `--overwrite`
 
-Regenerates the entire `.react-compiler-tracker.json` by scanning all supported source files (`src/**/*.{js,jsx,ts,tsx}`). Useful for initialization or picking up changes from skipped Git hooks.
+Regenerates the entire records file by scanning all source files matching `sourceGlob`. Useful for initialization or picking up changes from skipped Git hooks.
 
 ```bash
 npx @doist/react-compiler-tracker --overwrite
 ```
 
-### `--stage-record-file`
+### `--stage-record-file <file1> <file2> ...`
 
-Checks Git staged files and updates the records. Exits with code 1 if errors increase (preventing the commit), otherwise updates `.react-compiler-tracker.json` for staged files.
+Checks the provided files and updates the records. Exits with code 1 if errors increase (preventing the commit), otherwise updates the records file for the checked files.
 
 ```bash
-npx @doist/react-compiler-tracker --stage-record-file
+npx @doist/react-compiler-tracker --stage-record-file src/components/Button.tsx src/hooks/useData.ts
 ```
 
+If no files are provided, exits cleanly with a success message.
+
 ### `--check-files <file1> <file2> ...`
 
 Checks specific files without updating records. Exits with code 1 if checked files show increased error counts (or new errors). Primarily for CI to ensure PRs don't introduce new compiler errors.
@@ -50,7 +92,7 @@ npx @doist/react-compiler-tracker --check-files src/components/Button.tsx src/ho
 
 ### No flags
 
-Checks all supported source files and reports the total error count. The records file is **not** updated in this mode.
+Checks all source files matching `sourceGlob` and reports the total error count. The records file is **not** updated in this mode.
 
 ```bash
 npx @doist/react-compiler-tracker
@@ -65,11 +107,13 @@ In `package.json`:
 ```json
 {
   "lint-staged": {
-    "src/**/*.{js,jsx,ts,tsx}": "npx @doist/react-compiler-tracker --stage-record-file"
+    "*.{js,jsx,ts,tsx}": "npx @doist/react-compiler-tracker --stage-record-file"
   }
 }
 ```
 
+With lint-staged, the matched files are automatically passed as arguments to the command.
+
 ### GitHub Actions CI
 
 ```yaml
@@ -82,6 +126,17 @@ In `package.json`:
     fi
 ```
 
+### Pre-commit hook (manual)
+
+```bash
+#!/bin/sh
+# Get staged files and pass them to the tracker
+FILES=$(git diff --diff-filter=ACMR --cached --name-only -- '*.tsx' '*.ts' '*.jsx' '*.js' | tr '\n' ' ')
+if [ -n "$FILES" ]; then
+  npx @doist/react-compiler-tracker --stage-record-file $FILES
+fi
+```
+
 ## License
 
 Released under the [MIT License](https://opensource.org/licenses/MIT).
@@ -0,0 +1,53 @@
+import { existsSync, readFileSync } from 'node:fs'
+import { join } from 'node:path'
+
+type Config = {
+    recordsFile: string
+    sourceGlob: string
+}
+
+const DEFAULT_CONFIG: Config = {
+    recordsFile: '.react-compiler.rec.json',
+    sourceGlob: 'src/**/*.{js,jsx,ts,tsx}',
+}
+
+const CONFIG_FILE_NAME = '.react-compiler-tracker.config.json'
+
+function isValidConfig(config: unknown): config is Partial<Config> {
+    if (typeof config !== 'object' || config === null || Array.isArray(config)) {
+        return false
+    }
+    const obj = config as Record<string, unknown>
+    if (obj.recordsFile !== undefined && typeof obj.recordsFile !== 'string') {
+        return false
+    }
+    if (obj.sourceGlob !== undefined && typeof obj.sourceGlob !== 'string') {
+        return false
+    }
+    return true
+}
+
+function loadConfig(): Config {
+    const configPath = join(process.cwd(), CONFIG_FILE_NAME)
+
+    if (!existsSync(configPath)) {
+        return { ...DEFAULT_CONFIG }
+    }
+
+    try {
+        const configContent = readFileSync(configPath, 'utf8')
+        const parsed: unknown = JSON.parse(configContent)
+        if (!isValidConfig(parsed)) {
+            throw new Error(`Invalid config file at ${configPath}`)
+        }
+
+        return {
+            ...DEFAULT_CONFIG,
+            ...parsed,
+        }
+    } catch (error) {
+        throw new Error(`Failed to parse config at ${configPath}: ${error}`)
+    }
+}
+
+export { type Config, DEFAULT_CONFIG, loadConfig }
@@ -0,0 +1,83 @@
+import { existsSync, readFileSync } from 'node:fs'
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { DEFAULT_CONFIG, loadConfig } from './config.mjs'
+
+vi.mock('node:fs', () => ({
+    existsSync: vi.fn(),
+    readFileSync: vi.fn(),
+}))
+
+afterEach(() => {
+    vi.clearAllMocks()
+})
+
+describe('loadConfig', () => {
+    it('returns defaults when no config file exists', () => {
+        vi.mocked(existsSync).mockReturnValue(false)
+
+        const result = loadConfig()
+
+        expect(result).toEqual(DEFAULT_CONFIG)
+    })
+
+    it('loads and merges user config correctly', () => {
+        vi.mocked(existsSync).mockReturnValue(true)
+        vi.mocked(readFileSync).mockReturnValue(
+            JSON.stringify({
+                recordsFile: 'custom-records.json',
+                sourceGlob: 'app/**/*.{ts,tsx}',
+            }),
+        )
+
+        const result = loadConfig()
+
+        expect(result).toEqual({
+            recordsFile: 'custom-records.json',
+            sourceGlob: 'app/**/*.{ts,tsx}',
+        })
+    })
+
+    it('handles partial config (only some fields specified)', () => {
+        vi.mocked(existsSync).mockReturnValue(true)
+        vi.mocked(readFileSync).mockReturnValue(
+            JSON.stringify({
+                sourceGlob: 'packages/frontend/**/*.tsx',
+            }),
+        )
+
+        const result = loadConfig()
+
+        expect(result).toEqual({
+            recordsFile: DEFAULT_CONFIG.recordsFile,
+            sourceGlob: 'packages/frontend/**/*.tsx',
+        })
+    })
+
+    it('throws when config file is invalid JSON', () => {
+        vi.mocked(existsSync).mockReturnValue(true)
+        // Trailing comma - a common mistake when editing JSON by hand
+        vi.mocked(readFileSync).mockReturnValue(`{
+            "recordsFile": ".react-compiler.rec.json",
+        }`)
+
+        expect(() => loadConfig()).toThrow('Failed to parse config')
+    })
+
+    it('throws when config has invalid field types', () => {
+        vi.mocked(existsSync).mockReturnValue(true)
+        vi.mocked(readFileSync).mockReturnValue(
+            JSON.stringify({
+                recordsFile: { path: '.react-compiler.rec.json' },
+            }),
+        )
+
+        expect(() => loadConfig()).toThrow('Invalid config file')
+    })
+
+    it('throws when config file contains an array instead of object', () => {
+        vi.mocked(existsSync).mockReturnValue(true)
+        vi.mocked(readFileSync).mockReturnValue(JSON.stringify([{ recordsFile: 'records.json' }]))
+
+        expect(() => loadConfig()).toThrow('Invalid config file')
+    })
+})
@@ -1,12 +1,13 @@
 import { execSync } from 'node:child_process'
-import { existsSync, readFileSync, rmSync } from 'node:fs'
+import { existsSync, readFileSync, rmSync, writeFileSync } from 'node:fs'
 import { dirname, join } from 'node:path'
 import { fileURLToPath } from 'node:url'
 import { afterEach, describe, expect, it } from 'vitest'
 
 const __dirname = dirname(fileURLToPath(import.meta.url))
 const fixtureDir = join(__dirname, '__fixtures__/sample-project')
 const recordsPath = join(fixtureDir, '.react-compiler.rec.json')
+const configPath = join(fixtureDir, '.react-compiler-tracker.config.json')
 
 function runCLI(args: string[] = [], cwd = fixtureDir): string {
     const cliPath = join(__dirname, 'index.mts')
@@ -27,6 +28,9 @@ describe('CLI', () => {
         if (existsSync(recordsPath)) {
             rmSync(recordsPath)
         }
+        if (existsSync(configPath)) {
+            rmSync(configPath)
+        }
     })
 
     it('runs check on all files when no flag provided', () => {
@@ -50,6 +54,12 @@ describe('CLI', () => {
         expect(() => JSON.parse(readFileSync(recordsPath, 'utf8'))).toThrow()
     })
 
+    it('errors when file does not exist', () => {
+        const output = runCLI(['--check-files', 'src/nonexistent-file.tsx'])
+
+        expect(output).toContain('File not found: src/nonexistent-file.tsx')
+    })
+
     it('accepts --overwrite flag', () => {
         const output = runCLI(['--overwrite'])
 
@@ -72,4 +82,93 @@ describe('CLI', () => {
             },
         })
     })
+
+    describe('--stage-record-file flag', () => {
+        it('exits cleanly when no files provided', () => {
+            const output = runCLI(['--stage-record-file'])
+
+            expect(output).toContain('✅ No files to check')
+        })
+
+        it('checks provided files and reports increased errors', () => {
+            const output = runCLI([
+                '--stage-record-file',
+                'src/bad-component.tsx',
+                'src/bad-hook.ts',
+            ])
+
+            expect(output).toContain(
+                '🔍 Checking 2 files for React Compiler errors and updating records…',
+            )
+            expect(output).toContain('React Compiler errors have increased in:')
+            expect(output).toContain('• src/bad-component.tsx: +1')
+            expect(output).toContain('• src/bad-hook.ts: +3')
+        })
+
+        it('checks provided files with existing records', () => {
+            // First create records
+            runCLI(['--overwrite'])
+
+            // Then check staged files - should pass since errors match records
+            const output = runCLI([
+                '--stage-record-file',
+                'src/bad-component.tsx',
+                'src/good-component.tsx',
+            ])
+
+            expect(output).toContain(
+                '🔍 Checking 2 files for React Compiler errors and updating records…',
+            )
+            // The staging step may fail in test environment due to gitignore,
+            // but the important thing is that error checking passed
+            expect(output).not.toContain('React Compiler errors have increased')
+        })
+    })
+
+    describe('config file', () => {
+        it('uses custom sourceGlob from config', () => {
+            writeFileSync(
+                configPath,
+                JSON.stringify({
+                    sourceGlob: 'src/**/*.tsx',
+                }),
+            )
+
+            const output = runCLI()
+
+            // Should only find .tsx files (2 instead of 4)
+            expect(output).toContain('🔍 Checking all 2 source files for React Compiler errors…')
+        })
+
+        it('uses custom recordsFile from config', () => {
+            const customRecordsPath = join(fixtureDir, 'custom-records.json')
+            writeFileSync(
+                configPath,
+                JSON.stringify({
+                    recordsFile: 'custom-records.json',
+                }),
+            )
+
+            try {
+                runCLI(['--overwrite'])
+
+                expect(existsSync(customRecordsPath)).toBe(true)
+                expect(existsSync(recordsPath)).toBe(false)
+
+                const records = JSON.parse(readFileSync(customRecordsPath, 'utf8'))
+                expect(records.files).toEqual({
+                    'src/bad-component.tsx': {
+                        CompileError: 1,
+                    },
+                    'src/bad-hook.ts': {
+                        CompileError: 3,
+                    },
+                })
+            } finally {
+                if (existsSync(customRecordsPath)) {
+                    rmSync(customRecordsPath)
+                }
+            }
+        })
+    })
 })