fix: handle sourcemap with empty script code

ref vitejs/vite-plugin-vue@7f73970

Author: sxzz

src/core/main.ts

@@ -193,14 +193,23 @@ export async function transformMain(
 
   let resolvedMap: RawSourceMap | undefined = undefined
   if (options.sourceMap) {
-    if (scriptMap && templateMap) {
-      // if the template is inlined into the main module (indicated by the presence
-      // of templateMap), we need to concatenate the two source maps.
-
+    // the mappings of the source map for the inlined template should be moved
+    // because the position does not include the script tag part.
+    // we also concatenate the two source maps while doing that.
+    if (templateMap) {
+      const from = scriptMap ?? {
+        file: filename,
+        sourceRoot: '',
+        version: 3,
+        sources: [],
+        sourcesContent: [],
+        names: [],
+        mappings: '',
+      }
       const gen = fromMap(
         // version property of result.map is declared as string
         // but actually it is `3`
-        scriptMap as Omit<RawSourceMap, 'version'> as TraceEncodedSourceMap,
+        from as Omit<RawSourceMap, 'version'> as TraceEncodedSourceMap,
       )
       const tracer = new TraceMap(
         // same above
@@ -228,8 +237,7 @@ export async function transformMain(
       // of the main module compile result, which has outdated sourcesContent.
       resolvedMap.sourcesContent = templateMap.sourcesContent
     } else {
-      // if one of `scriptMap` and `templateMap` is empty, use the other one
-      resolvedMap = scriptMap ?? templateMap
+      resolvedMap = scriptMap
     }
   }