[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>;
```
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 7417fdd..36b528d 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -301,6 +301,9 @@
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 d528664..a82aea1 100644
--- a/clang/lib/Parse/Parser.cpp
+++ b/clang/lib/Parse/Parser.cpp
@@ -1049,6 +1049,8 @@
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 0000000..1301f2f
--- /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}}
