fix(vitest): add more type guards for --merge-reports

packages/vitest/src/node/reporters/blob.ts

@@ -1,4 +1,4 @@
-import { mkdir, readFile, readdir, writeFile } from 'node:fs/promises'
+import { mkdir, readFile, readdir, stat, writeFile } from 'node:fs/promises'
 import { existsSync } from 'node:fs'
 import { parse, stringify } from 'flatted'
 import { dirname, resolve } from 'pathe'
@@ -79,18 +79,37 @@ export async function readBlobs(
   // using process.cwd() because --merge-reports can only be used in CLI
   const resolvedDir = resolve(process.cwd(), blobsDirectory)
   const blobsFiles = await readdir(resolvedDir)
-  const promises = blobsFiles.map(async (file) => {
-    const content = await readFile(resolve(resolvedDir, file), 'utf-8')
+  const promises = blobsFiles.map(async (filename) => {
+    const fullPath = resolve(resolvedDir, filename)
+    const stats = await stat(fullPath)
+    if (!stats.isFile()) {
+      throw new TypeError(
+        `vitest.mergeReports() expects all paths in "${blobsDirectory}" to be files generated by the blob reporter, but "${filename}" is not a file`,
+      )
+    }
+    const content = await readFile(fullPath, 'utf-8')
     const [version, files, errors, moduleKeys, coverage] = parse(
       content,
     ) as MergeReport
-    return { version, files, errors, moduleKeys, coverage }
+    if (!version) {
+      throw new TypeError(
+        `vitest.mergeReports() expects all paths in "${blobsDirectory}" to be files generated by the blob reporter, but "${filename}" is not a valid blob file`,
+      )
+    }
+    return { version, files, errors, moduleKeys, coverage, file: filename }
   })
   const blobs = await Promise.all(promises)
 
   if (!blobs.length) {
     throw new Error(
-      `vitest.mergeReports() requires at least one blob file paths in the config`,
+      `vitest.mergeReports() requires at least one blob file in "${blobsDirectory}" directory, but none were found`,
+    )
+  }
+
+  const versions = new Set(blobs.map(blob => blob.version))
+  if (versions.size > 1) {
+    throw new Error(
+      `vitest.mergeReports() requires all blob files to be generated by the same Vitest version, received\n\n${blobs.map(b => `- "${b.file}" uses v${b.version}`).join('\n')}`,
     )
   }