[clang] [Clang] handle both gnu and cpp11 attributes to ensure correct parsing inside extern block (PR #102864)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Oleksandr T. (a-tarasyuk)

<details>
<summary>Changes</summary>

Fixes #<!-- -->101990

---
Full diff: https://github.com/llvm/llvm-project/pull/102864.diff


3 Files Affected:

- (modified) clang/docs/ReleaseNotes.rst (+1) 
- (modified) clang/lib/Parse/ParseDeclCXX.cpp (+4-1) 
- (modified) clang/test/Parser/attr-order.cpp (+8) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 6796a619ba97f8..00a663fdd23454 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -217,6 +217,7 @@ Bug Fixes to C++ Support
 - Clang now preserves the unexpanded flag in a lambda transform used for pack expansion. (#GH56852), (#GH85667),
   (#GH99877).
 - Fixed a bug when diagnosing ambiguous explicit specializations of constrained member functions.
+- Clang now properly handles the order of attributes in `extern` blocks. (#GH101990).
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index aac89d910bbc83..d45a738fe4c596 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -425,7 +425,10 @@ Decl *Parser::ParseLinkage(ParsingDeclSpec &DS, DeclaratorContext Context) {
       [[fallthrough]];
     default:
       ParsedAttributes DeclAttrs(AttrFactory);
-      MaybeParseCXX11Attributes(DeclAttrs);
+      ParsedAttributes DeclSpecAttrs(AttrFactory);
+      while (MaybeParseCXX11Attributes(DeclAttrs) ||
+             MaybeParseGNUAttributes(DeclSpecAttrs))
+        ;
       ParseExternalDeclaration(DeclAttrs, DeclSpecAttrs);
       continue;
     }
diff --git a/clang/test/Parser/attr-order.cpp b/clang/test/Parser/attr-order.cpp
index 10bad38cac6447..369941ab24ee69 100644
--- a/clang/test/Parser/attr-order.cpp
+++ b/clang/test/Parser/attr-order.cpp
@@ -31,3 +31,11 @@ template <int a>
 
 template <int a>
 [[noreturn]] __declspec(dllexport) __attribute__((cdecl)) void k(); // ok
+
+extern "C" {
+  __attribute__ ((__warn_unused_result__)) [[__maybe_unused__]] int l(int); // ok
+  [[__maybe_unused__]] __attribute__ ((__warn_unused_result__)) int m(int); // ok
+}
+
+extern "C" __attribute__ ((__warn_unused_result__)) [[__maybe_unused__]] int n(int); // ok
+extern "C" [[__maybe_unused__]] __attribute__ ((__warn_unused_result__)) int o(int); // ok

``````````

</details>


https://github.com/llvm/llvm-project/pull/102864