[clang] [Clang][Sema]: Allow flexible arrays in unions and alone in structs (PR #84428)

[Kees Cook via cfe-commits]

================
@@ -1,13 +1,158 @@
-// RUN: %clang_cc1 %s -verify=c -fsyntax-only
-// RUN: %clang_cc1 %s -verify -fsyntax-only -x c++
-// RUN: %clang_cc1 %s -verify -fsyntax-only -fms-compatibility
-// RUN: %clang_cc1 %s -verify -fsyntax-only -fms-compatibility -x c++
+// RUN: %clang_cc1 %s -verify=stock,c -fsyntax-only
+// RUN: %clang_cc1 %s -verify=stock,cpp -fsyntax-only -x c++
+// RUN: %clang_cc1 %s -verify=stock,cpp -fsyntax-only -fms-compatibility -x c++
+// RUN: %clang_cc1 %s -verify=stock,c,gnu -fsyntax-only -Wgnu-flexible-array-union-member -Wgnu-empty-struct
+// RUN: %clang_cc1 %s -verify=stock,c,microsoft -fsyntax-only -fms-compatibility -Wmicrosoft
 
 // The test checks that an attempt to initialize union with flexible array
 // member with an initializer list doesn't crash clang.
 
 
-union { char x[]; } r = {0}; // c-error {{flexible array member 'x' in a union is not allowed}}
+union { char x[]; } r = {0}; /* gnu-warning {{flexible array member 'x' in a union is a GNU extension}}
----------------
kees wrote:

It looks like clang/test/CodeGen/object-size.c (via commit 804af933f7310f78d91e13ad8a13b64b00249614) already covers a lot of this? I'll explicitly add unions to that test too.

https://github.com/llvm/llvm-project/pull/84428