feat: Add validateFilesExist to error on missing files

Files that don't exist now throw an error instead of being silently
ignored. This provides clear feedback when lint-staged passes a path
to a file that was deleted.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: frankieyan

src/index.integration.test.mts

@@ -54,6 +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'])
 

src/index.mts

@@ -47,6 +47,7 @@ async function main() {
                     filePaths: sourceFiles.normalizeFilePaths(filePathParams),
                     globPattern: config.sourceGlob,
                 })
+                sourceFiles.validateFilesExist(filePaths)
 
                 return await runStageRecords({
                     filePaths,
@@ -65,6 +66,7 @@ async function main() {
                     filePaths: sourceFiles.normalizeFilePaths(filePathParams),
                     globPattern: config.sourceGlob,
                 })
+                sourceFiles.validateFilesExist(filePaths)
 
                 return await runCheckFiles({ filePaths, recordsFilePath: config.recordsFile })
             }

src/source-files.mts

@@ -1,4 +1,5 @@
 import { execSync } from 'node:child_process'
+import { existsSync } from 'node:fs'
 import { relative } from 'node:path'
 import { glob } from 'glob'
 import { minimatch } from 'minimatch'
@@ -71,4 +72,16 @@ function filterByGlob({ filePaths, globPattern }: { filePaths: string[]; globPat
     return filePaths.filter((filePath) => minimatch(filePath, globPattern))
 }
 
-export { getAll, normalizeFilePaths, filterByGlob }
+/**
+ * Validates that all file paths exist on the filesystem.
+ * Throws an error if any file is not found.
+ */
+function validateFilesExist(filePaths: string[]) {
+    for (const filePath of filePaths) {
+        if (!existsSync(filePath)) {
+            throw new Error(`File not found: ${filePath}`)
+        }
+    }
+}
+
+export { getAll, normalizeFilePaths, filterByGlob, validateFilesExist }

src/source-files.test.mts

@@ -1,12 +1,17 @@
 import { execSync } from 'node:child_process'
+import { existsSync } from 'node:fs'
 import { glob } from 'glob'
 import { afterEach, describe, expect, it, vi } from 'vitest'
-import { filterByGlob, getAll, normalizeFilePaths } from './source-files.mjs'
+import { filterByGlob, getAll, normalizeFilePaths, validateFilesExist } from './source-files.mjs'
 
 vi.mock('node:child_process', () => ({
     execSync: vi.fn(),
 }))
 
+vi.mock('node:fs', () => ({
+    existsSync: vi.fn(),
+}))
+
 vi.mock('glob', () => ({
     glob: {
         sync: vi.fn(),
@@ -152,3 +157,27 @@ describe('filterByGlob', () => {
         expect(result).toEqual(['src/a.ts', 'src/b.tsx'])
     })
 })
+
+describe('validateFilesExist', () => {
+    it('throws error when file does not exist', () => {
+        vi.mocked(existsSync).mockReturnValue(false)
+
+        expect(() => validateFilesExist(['nonexistent.tsx'])).toThrow(
+            'File not found: nonexistent.tsx',
+        )
+    })
+
+    it('does not throw when all files exist', () => {
+        vi.mocked(existsSync).mockReturnValue(true)
+
+        expect(() => validateFilesExist(['exists.tsx'])).not.toThrow()
+    })
+
+    it('throws on first missing file', () => {
+        vi.mocked(existsSync).mockImplementation((path) => path === 'exists.tsx')
+
+        expect(() => validateFilesExist(['exists.tsx', 'missing.tsx'])).toThrow(
+            'File not found: missing.tsx',
+        )
+    })
+})