1 files changed, 23 insertions, 0 deletions
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 6202391ee0b..aba7049b0a5 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -9529,6 +9529,29 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
     }
   }
 
+  // Diagnose no_builtin attribute on function declaration that are not a
+  // definition.
+  // FIXME: We should really be doing this in
+  // SemaDeclAttr.cpp::handleNoBuiltinAttr, unfortunately we only have access to
+  // the FunctionDecl and at this point of the code
+  // FunctionDecl::isThisDeclarationADefinition() which always returns `false`
+  // because Sema::ActOnStartOfFunctionDef has not been called yet.
+  if (const auto *NBA = NewFD->getAttr<NoBuiltinAttr>())
+    switch (D.getFunctionDefinitionKind()) {
+    case FDK_Defaulted:
+    case FDK_Deleted:
+      Diag(NBA->getLocation(),
+           diag::err_attribute_no_builtin_on_defaulted_deleted_function)
+          << NBA->getSpelling();
+      break;
+    case FDK_Declaration:
+      Diag(NBA->getLocation(), diag::err_attribute_no_builtin_on_non_definition)
+          << NBA->getSpelling();
+      break;
+    case FDK_Definition:
+      break;
+    }
+
   return NewFD;
 }