[Frontend] Treat empty diagnostic category as "not present"

xedin · xedin · commit 782f7f17c8e6 · 2025-03-06T13:28:34.000-08:00
Serialized diagnostic stores an `std::string` which means that
the category gets marked as present even if its empty, which is
incorrect.
diff --git a/lib/Frontend/CachedDiagnostics.cpp b/lib/Frontend/CachedDiagnostics.cpp
@@ -617,7 +617,7 @@ llvm::Error DiagnosticSerializer::deserializeDiagnosticInfo(
                                   Kind,
                                   Info.FormatString,
                                   {},
-                                  Info.Category,
+                                  Info.Category.empty() ? StringRef() : Info.Category,
                                   *BICD,
                                   ChildDiagPtrs,
                                   Ranges,
