fix(coverage): c8 to log warning when run in Stackblitz (#2735)

packages/coverage-c8/package.json

@@ -43,6 +43,8 @@
   },
   "dependencies": {
     "c8": "^7.12.0",
+    "picocolors": "^1.0.0",
+    "std-env": "^3.3.1",
     "vitest": "workspace:*"
   },
   "devDependencies": {

packages/coverage-c8/src/provider.ts

@@ -3,6 +3,8 @@ import _url from 'url'
 import type { Profiler } from 'inspector'
 import { takeCoverage } from 'v8'
 import { extname, resolve } from 'pathe'
+import c from 'picocolors'
+import { provider } from 'std-env'
 import type { RawSourceMap } from 'vite-node'
 import { coverageConfigDefaults } from 'vitest/config'
 // eslint-disable-next-line no-restricted-imports
@@ -52,6 +54,9 @@ export class C8CoverageProvider implements CoverageProvider {
   async reportCoverage({ allTestsRun }: ReportContext = {}) {
     takeCoverage()
 
+    if (provider === 'stackblitz')
+      this.ctx.logger.log(c.blue(' % ') + c.yellow('@vitest/coverage-c8 does not work on Stackblitz. Report will be empty.'))
+
     const options: ConstructorParameters<typeof Report>[0] = {
       ...this.options,
       all: this.options.all && allTestsRun,