perf: skip computing sourceRoot in injectSourcesContent (#15207)

packages/vite/src/node/server/sourcemap.ts

@@ -19,40 +19,56 @@ interface SourceMapLike {
   sourceRoot?: string
 }
 
-export async function injectSourcesContent(
-  map: SourceMapLike,
-  file: string,
-  logger: Logger,
-): Promise<void> {
+async function computeSourceRoute(map: SourceMapLike, file: string) {
   let sourceRoot: string | undefined
   try {
     // The source root is undefined for virtual modules and permission errors.
     sourceRoot = await fsp.realpath(
       path.resolve(path.dirname(file), map.sourceRoot || ''),
     )
   } catch {}
+  return sourceRoot
+}
+
+export async function injectSourcesContent(
+  map: SourceMapLike,
+  file: string,
+  logger: Logger,
+): Promise<void> {
+  let sourceRootPromise: Promise<string | undefined>
 
   const missingSources: string[] = []
   const sourcesContent = map.sourcesContent || []
-  await Promise.all(
-    map.sources.map(async (sourcePath, index) => {
-      let content = null
-      if (sourcePath && !virtualSourceRE.test(sourcePath)) {
-        sourcePath = decodeURI(sourcePath)
-        if (sourceRoot) {
-          sourcePath = path.resolve(sourceRoot, sourcePath)
-        }
-        // inject content from source file when sourcesContent is null
-        content =
-          sourcesContent[index] ??
-          (await fsp.readFile(sourcePath, 'utf-8').catch(() => {
-            missingSources.push(sourcePath)
-            return null
-          }))
-      }
-      sourcesContent[index] = content
-    }),
-  )
+  const sourcesContentPromises: Promise<void>[] = []
+  for (let index = 0; index < map.sources.length; index++) {
+    const sourcePath = map.sources[index]
+    if (
+      !sourcesContent[index] &&
+      sourcePath &&
+      !virtualSourceRE.test(sourcePath)
+    ) {
+      sourcesContentPromises.push(
+        (async () => {
+          // inject content from source file when sourcesContent is null
+          sourceRootPromise ??= computeSourceRoute(map, file)
+          const sourceRoot = await sourceRootPromise
+          let resolvedSourcePath = decodeURI(sourcePath)
+          if (sourceRoot) {
+            resolvedSourcePath = path.resolve(sourceRoot, resolvedSourcePath)
+          }
+
+          sourcesContent[index] = await fsp
+            .readFile(resolvedSourcePath, 'utf-8')
+            .catch(() => {
+              missingSources.push(resolvedSourcePath)
+              return null
+            })
+        })(),
+      )
+    }
+  }
+
+  await Promise.all(sourcesContentPromises)
 
   map.sourcesContent = sourcesContent