From 17646ac7294e02200082bc40225d3158d5e3451b Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Tue, 18 Aug 2026 15:59:56 +0900
Subject: [PATCH] fix(snapshot): reject when `toMatchFileSnapshot` uses same
 snapshot file as `toMatchSnapshot` (#10978)

Co-authored-by: Hiroshi Ogawa <4232207+hi-ogawa@users.noreply.github.com>
Co-authored-by: OpenCode <noreply@opencode.ai>
Co-authored-by: Vladimir <sleuths.slews0s@icloud.com>
---
 docs/guide/snapshot.md          |  4 +++
 packages/snapshot/src/client.ts |  8 ++++++
 test/e2e/snapshots/file.test.ts | 46 ++++++++++++++++++++++++++++++++-
 3 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/docs/guide/snapshot.md b/docs/guide/snapshot.md
index df11944d2..69acc1076 100644
--- a/docs/guide/snapshot.md
+++ b/docs/guide/snapshot.md
@@ -108,6 +108,10 @@ it('render basic', async () => {
 
 It will compare with the content of `./test/basic.output.html`. And can be written back with the `--update` flag.
 
+::: warning
+Do not use a snapshot path managed by Vitest, such as `__snapshots__/basic.test.ts.snap`, with `toMatchFileSnapshot`. Choose a separate file path pattern for file snapshots.
+:::
+
 ## Visual Snapshots
 
 For visual regression testing of UI components and pages, Vitest provides built-in support through [browser mode](/guide/browser/) with the [`toMatchScreenshot()`](/api/browser/assertions#tomatchscreenshot) assertion:
diff --git a/packages/snapshot/src/client.ts b/packages/snapshot/src/client.ts
index 9a398cfbd..85aa7f3fd 100644
--- a/packages/snapshot/src/client.ts
+++ b/packages/snapshot/src/client.ts
@@ -135,6 +135,14 @@ export class SnapshotClient {
     }
 
     const snapshotState = this.getSnapshotState(filepath)
+    if (rawSnapshot?.file === snapshotState.snapshotPath) {
+      // note that this hard rejection is best-effort in a sense that,
+      // if `toMatchFileSnapshot` is called with a different test file's snapshot path,
+      // this check will not catch it.
+      throw new Error(
+        `File snapshot cannot use the same path as the test snapshot file: ${rawSnapshot.file}`,
+      )
+    }
     const testName = [name, ...(message ? [message] : [])].join(' > ')
 
     // Probe first so we can mark as checked even on early return
diff --git a/test/e2e/snapshots/file.test.ts b/test/e2e/snapshots/file.test.ts
index 0aa5b246b..fa4d37f8e 100644
--- a/test/e2e/snapshots/file.test.ts
+++ b/test/e2e/snapshots/file.test.ts
@@ -1,6 +1,6 @@
 import { join } from 'node:path'
 import { expect, test } from 'vitest'
-import { editFile, runVitest } from '../../test-utils'
+import { editFile, runInlineTests, runVitest } from '../../test-utils'
 
 test('white space sensitive', async () => {
   const root = join(import.meta.dirname, 'fixtures/file')
@@ -26,3 +26,47 @@ test('white space sensitive', async () => {
 `)
   expect(vitest.exitCode).toBe(1)
 })
+
+test('file snapshot cannot use the test snapshot path', async () => {
+  const result = await runInlineTests({
+    'basic.test.ts': `
+import { expect, test } from 'vitest'
+
+test('file snapshot', async () => {
+  await expect('content').toMatchFileSnapshot('__snapshots__/basic.test.ts.snap')
+})
+`,
+  })
+
+  expect(result.errorTree()).toMatchInlineSnapshot(`
+    {
+      "basic.test.ts": {
+        "file snapshot": [
+          "File snapshot cannot use the same path as the test snapshot file: <root>/__snapshots__/basic.test.ts.snap",
+        ],
+      },
+    }
+  `)
+})
+
+test('file snapshot can use another test filename', async () => {
+  const result = await runInlineTests({
+    'other.test.ts': `
+import { expect, test } from 'vitest'
+
+test('file snapshot', async () => {
+  await expect('content').toMatchFileSnapshot('__snapshots__/basic.test.ts.snap')
+})
+`,
+  }, { update: true })
+
+  expect(result.stderr).toBe('')
+  expect(result.testTree()).toMatchInlineSnapshot(`
+    {
+      "other.test.ts": {
+        "file snapshot": "passed",
+      },
+    }
+  `)
+  expect(result.fs.readFile('__snapshots__/basic.test.ts.snap')).toBe('content')
+})
-- 
2.51.2