feat: show warning if root is in build.outDir (#16454)

Author: sapphi-red

packages/vite/src/node/config.ts

@@ -45,6 +45,7 @@ import {
   isFilePathESM,
   isNodeBuiltin,
   isObject,
+  isParentDirectory,
   mergeAlias,
   mergeConfig,
   normalizeAlias,
@@ -914,6 +915,20 @@ assetFileNames isn't equal for every build.rollupOptions.output. A single patter
     )
   }
 
+  const resolvedBuildOutDir = normalizePath(
+    path.resolve(resolved.root, resolved.build.outDir),
+  )
+  if (
+    isParentDirectory(resolvedBuildOutDir, resolved.root) ||
+    resolvedBuildOutDir === resolved.root
+  ) {
+    resolved.logger.warn(
+      colors.yellow(`
+(!) build.outDir must not be the same directory of root or a parent directory of root as this could cause Vite to overwriting source files with build outputs.
+`),
+    )
+  }
+
   return resolved
 }