[clang] 08b0c25 - [Clang] disallow use of attributes before extern template declarations (#136328)

[via cfe-commits]

Author: Oleksandr T.
Date: 2025-04-21T18:12:07+03:00
New Revision: 08b0c2517eb859667d59873bf04b6aa78a7583a7

URL: https://github.com/llvm/llvm-project/commit/08b0c2517eb859667d59873bf04b6aa78a7583a7
DIFF: https://github.com/llvm/llvm-project/commit/08b0c2517eb859667d59873bf04b6aa78a7583a7.diff

LOG: [Clang] disallow use of attributes before extern template declarations (#136328)

Fixes #79893 


--- 

This PR addresses the issue of _attributes_ being incorrectly allowed on
`extern template` declarations

```cpp
[[deprecated]] extern template struct S<int>;
```

Added: 
    clang/test/Parser/extern-template-attributes.cpp

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/lib/Parse/Parser.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 7417fdd71a392..36b528d9e20f8 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -301,6 +301,9 @@ related warnings within the method body.
   particularly relevant for AMDGPU targets, where they map to corresponding IR
   metadata.
 
+- Clang now disallows the use of attributes applied before an
+  ``extern template`` declaration (#GH79893).
+
 Improvements to Clang's diagnostics
 -----------------------------------
 

diff  --git a/clang/lib/Parse/Parser.cpp b/clang/lib/Parse/Parser.cpp
index d528664bca352..a82aea162716a 100644
--- a/clang/lib/Parse/Parser.cpp
+++ b/clang/lib/Parse/Parser.cpp
@@ -1049,6 +1049,8 @@ Parser::ParseExternalDeclaration(ParsedAttributes &Attrs,
 
   case tok::kw_extern:
     if (getLangOpts().CPlusPlus && NextToken().is(tok::kw_template)) {
+      ProhibitAttributes(Attrs);
+      ProhibitAttributes(DeclSpecAttrs);
       // Extern templates
       SourceLocation ExternLoc = ConsumeToken();
       SourceLocation TemplateLoc = ConsumeToken();

diff  --git a/clang/test/Parser/extern-template-attributes.cpp b/clang/test/Parser/extern-template-attributes.cpp
new file mode 100644
index 0000000000000..1301f2f680ccb
--- /dev/null
+++ b/clang/test/Parser/extern-template-attributes.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -std=c++17 -fms-extensions -verify %s
+
+template <class>
+struct S {};
+
+[[deprecated]] extern template struct S<int>;              // expected-error {{an attribute list cannot appear here}}
+__attribute__((deprecated)) extern template struct S<int>; // expected-error {{an attribute list cannot appear here}}
+__declspec(deprecated) extern template struct S<int>;      // expected-error {{expected unqualified-id}}