feat(config): add snapshotSerializers option (#5092)

docs/config/index.md

@@ -1662,9 +1662,16 @@ Format options for snapshot testing. These options are passed down to [`pretty-f
 ::: tip
 Beware that `plugins` field on this object will be ignored.
 
-If you need to extend snapshot serializer via pretty-format plugins, please, use [`expect.addSnapshotSerializer`](/api/expect#expect-addsnapshotserializer) API.
+If you need to extend snapshot serializer via pretty-format plugins, please, use [`expect.addSnapshotSerializer`](/api/expect#expect-addsnapshotserializer) API or [snapshotSerializers](#snapshotserializers-1-3-0) option.
 :::
 
+### snapshotSerializers<NonProjectOption /> <Badge type="info">1.3.0+</Badge>
+
+- **Type:** `string[]`
+- **Default:** `[]`
+
+A list of paths to snapshot serializer modules for snapshot testing, useful if you want add custom snapshot serializers. See [Custom Serializer](/guide/snapshot#custom-serializer) for more information.
+
 ### resolveSnapshotPath<NonProjectOption />
 
 - **Type**: `(testPath: string, snapExtension: string) => string`

docs/guide/snapshot.md

@@ -117,7 +117,7 @@ You can learn more in the [`examples/image-snapshot`](https://github.com/vitest-
 
 You can add your own logic to alter how your snapshots are serialized. Like Jest, Vitest has default serializers for built-in JavaScript types, HTML elements, ImmutableJS and for React elements.
 
-Example serializer module:
+You can explicitly add custom serializer by using [`expect.addSnapshotSerializer`](/api/expect#expect-addsnapshotserializer) API.
 
 ```ts
 expect.addSnapshotSerializer({
@@ -137,6 +137,39 @@ expect.addSnapshotSerializer({
 })
 ```
 
+We also support [snapshotSerializers](/config/#snapshotserializers-1-3-0) option to implicitly add custom serializers.
+
+```ts
+import { SnapshotSerializer } from 'vitest'
+
+export default {
+  serialize(val, config, indentation, depth, refs, printer) {
+    // `printer` is a function that serializes a value using existing plugins.
+    return `Pretty foo: ${printer(
+      val.foo,
+      config,
+      indentation,
+      depth,
+      refs,
+    )}`
+  },
+  test(val) {
+    return val && Object.prototype.hasOwnProperty.call(val, 'foo')
+  },
+} satisfies SnapshotSerializer
+```
+
+
+```ts
+import { defineConfig } from 'vite'
+
+export default defineConfig({
+  test: {
+    snapshotSerializers: ['path/to/custom-serializer.ts']
+  },
+})
+```
+
 After adding a test like this:
 
 ```ts

packages/browser/src/client/main.ts

@@ -211,6 +211,7 @@ async function prepareTestEnvironment(config: ResolvedConfig) {
     startTests,
     setupCommonEnv,
     loadDiffConfig,
+    loadSnapshotSerializers,
     takeCoverageInsideWorker,
   } = await importId('vitest/browser') as typeof import('vitest/browser')
 
@@ -228,6 +229,7 @@ async function prepareTestEnvironment(config: ResolvedConfig) {
     startTests,
     setupCommonEnv,
     loadDiffConfig,
+    loadSnapshotSerializers,
     executor,
     runner,
   }
@@ -244,7 +246,7 @@ async function runTests(paths: string[], config: ResolvedConfig) {
     return
   }
 
-  const { startTests, setupCommonEnv, loadDiffConfig, executor, runner } = preparedData!
+  const { startTests, setupCommonEnv, loadDiffConfig, loadSnapshotSerializers, executor, runner } = preparedData!
 
   onCancel.then((reason) => {
     runner?.onCancel?.(reason)
@@ -254,7 +256,11 @@ async function runTests(paths: string[], config: ResolvedConfig) {
     config.snapshotOptions.snapshotEnvironment = new BrowserSnapshotEnvironment()
 
   try {
-    runner.config.diffOptions = await loadDiffConfig(config, executor as VitestExecutor)
+    const [diffOptions] = await Promise.all([
+      loadDiffConfig(config, executor as VitestExecutor),
+      loadSnapshotSerializers(config, executor as VitestExecutor),
+    ])
+    runner.config.diffOptions = diffOptions
 
     await setupCommonEnv(config)
     const files = paths.map((path) => {

packages/snapshot/src/index.ts

@@ -10,6 +10,7 @@ export type {
   SnapshotStateOptions,
   SnapshotMatchOptions,
   SnapshotResult,
+  SnapshotSerializer,
   UncheckedSnapshot,
   SnapshotSummary,
 } from './types'

packages/snapshot/src/types/index.ts

@@ -1,4 +1,4 @@
-import type { OptionsReceived as PrettyFormatOptions } from 'pretty-format'
+import type { OptionsReceived as PrettyFormatOptions, Plugin as PrettyFormatPlugin } from 'pretty-format'
 import type { RawSnapshotInfo } from '../port/rawSnapshot'
 import type { SnapshotEnvironment, SnapshotEnvironmentOptions } from './environment'
 
@@ -7,6 +7,8 @@ export type SnapshotData = Record<string, string>
 
 export type SnapshotUpdateState = 'all' | 'new' | 'none'
 
+export type SnapshotSerializer = PrettyFormatPlugin
+
 export interface SnapshotStateOptions {
   updateSnapshot: SnapshotUpdateState
   snapshotEnvironment: SnapshotEnvironment

packages/vitest/src/browser.ts

@@ -1,3 +1,3 @@
 export { startTests, processError } from '@vitest/runner'
-export { setupCommonEnv, loadDiffConfig } from './runtime/setup-common'
+export { setupCommonEnv, loadDiffConfig, loadSnapshotSerializers } from './runtime/setup-common'
 export { takeCoverageInsideWorker, stopCoverageInsideWorker, getCoverageProvider, startCoverageInsideWorker } from './integrations/coverage'

packages/vitest/src/node/config.ts

@@ -234,6 +234,12 @@ export function resolveConfig(
     snapshotEnvironment: null as any,
   }
 
+  resolved.snapshotSerializers ??= []
+  resolved.snapshotSerializers = resolved.snapshotSerializers.map(file =>
+    resolvePath(file, resolved.root),
+  )
+  resolved.forceRerunTriggers.push(...resolved.snapshotSerializers)
+
   if (options.resolveSnapshotPath)
     delete (resolved as UserConfig).resolveSnapshotPath
 

packages/vitest/src/runtime/runners/index.ts

@@ -6,7 +6,7 @@ import { distDir } from '../../paths'
 import { getWorkerState } from '../../utils/global'
 import { rpc } from '../rpc'
 import { takeCoverageInsideWorker } from '../../integrations/coverage'
-import { loadDiffConfig } from '../setup-common'
+import { loadDiffConfig, loadSnapshotSerializers } from '../setup-common'
 
 const runnersFile = resolve(distDir, 'runners.js')
 
@@ -38,7 +38,11 @@ export async function resolveTestRunner(config: ResolvedConfig, executor: Vitest
   if (!testRunner.importFile)
     throw new Error('Runner must implement "importFile" method.')
 
-  testRunner.config.diffOptions = await loadDiffConfig(config, executor)
+  const [diffOptions] = await Promise.all([
+    loadDiffConfig(config, executor),
+    loadSnapshotSerializers(config, executor),
+  ])
+  testRunner.config.diffOptions = diffOptions
 
   // patch some methods, so custom runners don't need to call RPC
   const originalOnTaskUpdate = testRunner.onTaskUpdate

packages/vitest/src/runtime/setup-common.ts

@@ -1,4 +1,6 @@
 import { setSafeTimers } from '@vitest/utils'
+import { addSerializer } from '@vitest/snapshot'
+import type { SnapshotSerializer } from '@vitest/snapshot'
 import { resetRunOnceCounter } from '../integrations/run-once'
 import type { ResolvedConfig } from '../types'
 import type { DiffOptions } from '../types/matcher-utils'
@@ -35,3 +37,23 @@ export async function loadDiffConfig(config: ResolvedConfig, executor: VitestExe
   else
     throw new Error(`invalid diff config file ${config.diff}. Must have a default export with config object`)
 }
+
+export async function loadSnapshotSerializers(config: ResolvedConfig, executor: VitestExecutor) {
+  const files = config.snapshotSerializers
+
+  const snapshotSerializers = await Promise.all(
+    files.map(async (file) => {
+      const mo = await executor.executeId(file)
+      if (!mo || typeof mo.default !== 'object' || mo.default === null)
+        throw new Error(`invalid snapshot serializer file ${file}. Must export a default object`)
+
+      const config = mo.default
+      if (typeof config.test !== 'function' || (typeof config.serialize !== 'function' && typeof config.print !== 'function'))
+        throw new Error(`invalid snapshot serializer in ${file}. Must have a 'test' method along with either a 'serialize' or 'print' method.`)
+
+      return config as SnapshotSerializer
+    }),
+  )
+
+  snapshotSerializers.forEach(serializer => addSerializer(serializer))
+}

packages/vitest/src/types/config.ts

@@ -533,6 +533,11 @@ export interface InlineConfig {
    */
   diff?: string
 
+  /**
+   * Paths to snapshot serializer modules.
+   */
+  snapshotSerializers?: string[]
+
   /**
    * Resolve custom snapshot path
    */

packages/vitest/src/types/snapshot.ts

@@ -6,4 +6,5 @@ export type {
   SnapshotResult,
   UncheckedSnapshot,
   SnapshotSummary,
+  SnapshotSerializer,
 } from '@vitest/snapshot'

test/snapshots/test/custom-serializers.test.ts

@@ -0,0 +1,11 @@
+import { expect, test } from 'vitest'
+import { runVitest } from '../../test-utils'
+
+test('it should pass', async () => {
+  const { stdout, stderr } = await runVitest({
+    root: 'test/fixtures/custom-serializers',
+  })
+
+  expect(stdout).toContain('✓ custom-serializers.test.ts >')
+  expect(stderr).toBe('')
+})

test/snapshots/test/fixtures/custom-serializers/custom-serializers.test.ts

@@ -0,0 +1,23 @@
+import { test, expect } from "vitest";
+
+test("", () => {
+  expect({foo: {
+    a: 1,
+    b: 2
+  }}).toMatchInlineSnapshot(`
+    Pretty foo: {
+      "a": 1,
+      "b": 2,
+    }
+  `);
+
+  expect({bar: {
+    a: 1,
+    b: 2
+  }}).toMatchInlineSnapshot(`
+    Pretty bar: {
+      "a": 1,
+      "b": 2,
+    }
+  `);
+})

test/snapshots/test/fixtures/custom-serializers/serializer-1.js

@@ -0,0 +1,14 @@
+export default {
+  serialize(val, config, indentation, depth, refs, printer) {
+    return `Pretty foo: ${printer(
+      val.foo,
+      config,
+      indentation,
+      depth,
+      refs,
+    )}`
+  },
+  test(val) {
+    return val && Object.prototype.hasOwnProperty.call(val, 'foo')
+  },
+}

test/snapshots/test/fixtures/custom-serializers/serializer-2.ts

@@ -0,0 +1,16 @@
+import { SnapshotSerializer } from 'vitest'
+
+export default {
+  serialize(val, config, indentation, depth, refs, printer) {
+    return `Pretty bar: ${printer(
+      val.bar,
+      config,
+      indentation,
+      depth,
+      refs,
+    )}`
+  },
+  test(val) {
+    return val && Object.prototype.hasOwnProperty.call(val, 'bar')
+  },
+} satisfies SnapshotSerializer

test/snapshots/test/fixtures/custom-serializers/vitest.config.ts

@@ -0,0 +1,7 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    snapshotSerializers: ['./serializer-1.js', './serializer-2.ts']
+  }
+})