[llvm] [Support] Handle delete_pending case for Windows fs::status (PR #90655)

[Alexandre Ganea via llvm-commits]

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@@ -785,9 +785,20 @@ std::error_code status(const Twine &path, file_status &result, bool Follow) {
 
   DWORD Flags = FILE_FLAG_BACKUP_SEMANTICS;
   if (!Follow) {
-    DWORD attr = ::GetFileAttributesW(path_utf16.begin());
-    if (attr == INVALID_FILE_ATTRIBUTES)
-      return getStatus(INVALID_HANDLE_VALUE, result);
+    DWORD attr;
+
+    // If getting file attributes fails due to a pending deletion, try
+    // again in a loop to avoid returning a misleading permission denied
+    // error.
+    for (int Retry = 200; Retry >= 0; --Retry) {
+      attr = ::GetFileAttributesW(path_utf16.begin());
+      if (attr != INVALID_FILE_ATTRIBUTES)
+        break;
+      std::error_code code = getStatus(INVALID_HANDLE_VALUE, result);
+      if (code != llvm::errc::delete_pending || !Retry)
+        return code;
+      ::Sleep(15);
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aganea wrote:

At the risk of [repeating myself](https://github.com/llvm/llvm-project/issues/89137#issuecomment-2077056218), I feel all this is caused by the lack of synchronization between processes that write the module units (in Apple's symbol index generation). The filesystem is used as a synchronization, but since you can't provide "scopes" like a mutex guard, you end up with this issue. Is that something that was considered in the application's design @z2oh ?

https://github.com/llvm/llvm-project/pull/90655