feat(experimental): expose matchesTagsFilter to test if the current filter matches tags

docs/guide/test-tags.md

@@ -300,3 +300,19 @@ You can also pass multiple `--tags-filter` flags. They are combined with AND log
 # Run tests that match (unit OR e2e) AND are NOT slow
 vitest --tags-filter="unit || e2e" --tags-filter="!slow"
 ```
+
+### Checking Tags Filter at Runtime
+
+You can use `TestRunner.matchesTagsFilter` (since Vitest 4.1.1) to check whether the current tags filter matches a set of tags. This is useful for conditionally running expensive setup logic only when relevant tests are included:
+
+```ts
+import { beforeAll, TestRunner } from 'vitest'
+
+beforeAll(async () => {
+  if (TestRunner.matchesTagsFilter(['db'])) {
+    await seedDatabase()
+  }
+})
+```
+
+The method accepts an array of tags and returns `true` if the current `--tags-filter` would include a test with those tags. If no tags filter is active, it always returns `true`.

packages/runner/src/collect.ts

@@ -36,6 +36,8 @@ export async function collectTests(
       'collect_spec',
       { 'code.file.path': filepath },
       async () => {
+        runner._currentSpecification = typeof spec === 'string' ? { filepath: spec } : spec
+
         const testLocations = typeof spec === 'string' ? undefined : spec.testLocations
         const testNamePattern = typeof spec === 'string' ? undefined : spec.testNamePattern
         const testIds = typeof spec === 'string' ? undefined : spec.testIds

packages/runner/src/types/runner.ts

@@ -55,10 +55,10 @@ export interface FileSpecification {
   // file can be marked via a jsdoc comment to have tags,
   // these are _not_ tags to filter tests by
   fileTags?: string[]
-  testLocations: number[] | undefined
-  testNamePattern: RegExp | undefined
-  testTagsFilter: string[] | undefined
-  testIds: string[] | undefined
+  testLocations?: number[] | undefined
+  testNamePattern?: RegExp | undefined
+  testTagsFilter?: string[] | undefined
+  testIds?: string[] | undefined
 }
 
 export interface TestTagDefinition extends Omit<TestOptions, 'tags' | 'shuffle'> {
@@ -231,8 +231,10 @@ export interface VitestRunner {
   // eslint-disable-next-line ts/method-signature-style
   trace?<T>(name: string, attributes: Record<string, any>, cb: () => T): T
 
-  /** @private */
+  /** @internal */
+  _currentSpecification?: FileSpecification | undefined
+  /** @internal */
   _currentTaskStartTime?: number
-  /** @private */
+  /** @internal */
   _currentTaskTimeout?: number
 }

packages/runner/src/utils/index.ts

@@ -10,7 +10,7 @@ export {
 } from './collect'
 export { limitConcurrency } from './limit-concurrency'
 export { partitionSuiteChildren } from './suite'
-export { createTagsFilter, validateTags } from './tags'
+export { createTagsFilter, matchesTagsFilter, validateTags } from './tags'
 export {
   createTaskName,
   getFullName,

packages/runner/src/utils/tags.ts

@@ -1,4 +1,21 @@
 import type { TestTagDefinition, VitestRunnerConfig } from '../types/runner'
+import { getRunner } from '../suite'
+
+const filterMap = new WeakMap<string[], (testTags: string[]) => boolean>()
+
+export function matchesTagsFilter(testTags: string[]): boolean {
+  const runner = getRunner()
+  const tagsFilter = runner._currentSpecification?.testTagsFilter ?? runner.config.tagsFilter
+  if (!tagsFilter) {
+    return true
+  }
+  let tagsFilterPredicate = filterMap.get(tagsFilter)
+  if (!tagsFilterPredicate) {
+    tagsFilterPredicate = createTagsFilter(tagsFilter, runner.config.tags)
+    filterMap.set(tagsFilter, tagsFilterPredicate)
+  }
+  return tagsFilterPredicate(testTags)
+}
 
 export function validateTags(config: VitestRunnerConfig, tags: string[]): void {
   if (!config.strictTags) {

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

@@ -22,7 +22,7 @@ import {
   getFn,
   getHooks,
 } from '@vitest/runner'
-import { createChainable, getNames, getTestName, getTests } from '@vitest/runner/utils'
+import { createChainable, getNames, getTestName, getTests, matchesTagsFilter } from '@vitest/runner/utils'
 import { processError } from '@vitest/utils/error'
 import { normalize } from 'pathe'
 import { createExpect } from '../../integrations/chai/index'
@@ -278,6 +278,7 @@ export class TestRunner implements VitestTestRunner {
   static getTestFn: typeof getFn = getFn
   static setSuiteHooks: typeof getHooks = getHooks
   static setTestFn: typeof getFn = getFn
+  static matchesTagsFilter: typeof matchesTagsFilter = matchesTagsFilter
 
   /**
    * @deprecated