fix(ssr): fix source map remapping with multiple sources

packages/vite/src/node/ssr/__tests__/fixtures/multi-source-sourcemaps/entrypoint.js

@@ -0,0 +1,12 @@
+/*
+ * You can rebuild this with:
+ * - rm -f ./dist.js ./dist.js.map
+ * - npx esbuild --bundle entrypoint.js --outfile=dist.js --sourcemap --format=esm
+ */
+
+import nested from './nested-directory/nested-file'
+
+export function entrypoint() {
+  console.log(nested)
+  throw new Error('Hello world')
+}

packages/vite/src/node/ssr/__tests__/fixtures/multi-source-sourcemaps/nested-directory/nested-file.js

@@ -0,0 +1 @@
+export default 'Nested file will trigger edge case that used to break sourcemaps'

packages/vite/src/node/ssr/__tests__/ssrTransform.spec.ts

@@ -441,6 +441,31 @@ test('sourcemap with multiple sources', async () => {
   }
 })
 
+test('sourcemap with multiple sources and nested paths', async () => {
+  const code = readFixture('dist.js')
+  const map = readFixture('dist.js.map')
+
+  const result = await ssrTransform(code, JSON.parse(map), '', code)
+  assert(result?.map)
+
+  const { sources } = result.map as SourceMap
+  expect(sources).toMatchInlineSnapshot(`
+    [
+      "nested-directory/nested-file.js",
+      "entrypoint.js",
+    ]
+  `)
+
+  function readFixture(filename: string) {
+    const url = new URL(
+      `./fixtures/multi-source-sourcemaps/${filename}`,
+      import.meta.url,
+    )
+
+    return readFileSync(fileURLToPath(url), 'utf8')
+  }
+})
+
 test('overwrite bindings', async () => {
   expect(
     await ssrTransformSimpleCode(

packages/vite/src/node/ssr/ssrTransform.ts

@@ -347,25 +347,20 @@ async function ssrTransformScript(
   })
 
   let map = s.generateMap({ hires: 'boundary' })
+  map.sources = [path.basename(url)]
+  // needs to use originalCode instead of code
+  // because code might be already transformed even if map is null
+  map.sourcesContent = [originalCode]
   if (
     inMap &&
     inMap.mappings &&
     'sources' in inMap &&
     inMap.sources.length > 0
   ) {
     map = combineSourcemaps(url, [
-      {
-        ...map,
-        sources: inMap.sources,
-        sourcesContent: inMap.sourcesContent,
-      } as RawSourceMap,
+      map as RawSourceMap,
       inMap as RawSourceMap,
     ]) as SourceMap
-  } else {
-    map.sources = [path.basename(url)]
-    // needs to use originalCode instead of code
-    // because code might be already transformed even if map is null
-    map.sourcesContent = [originalCode]
   }
 
   return {