[clang] [clang] diagnose block pointer types as invalid for constant template parameters (PR #190464)

[via cfe-commits]

https://github.com/Serosh-commits updated https://github.com/llvm/llvm-project/pull/190464

>From 6645f88d531dd0cdc442ac163571c731464ba620 Mon Sep 17 00:00:00 2001
From: Serosh-commits <janmejayapanda400 at gmail.com>
Date: Sun, 5 Apr 2026 05:08:24 +0530
Subject: [PATCH] [Clang] Diagnose block pointer types as invalid for constant
 template parameters

---
 clang/docs/ReleaseNotes.rst     | 1 +
 clang/lib/Sema/SemaTemplate.cpp | 5 +++++
 clang/test/SemaCXX/blocks.cpp   | 4 ++++
 3 files changed, 10 insertions(+)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 2fe76e60946f5..1601be699a604 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -412,6 +412,7 @@ Bug Fixes to Attribute Support
 
 Bug Fixes to C++ Support
 ^^^^^^^^^^^^^^^^^^^^^^^^
+- Clang now rejects constant template parameters with block pointer types, since these are not implemented anyway and would lead to crashes. (#GH189247)
 - Fixed a crash on error recovery when dealing with invalid templates. (#GH183075)
 - Fixed a crash when instantiating ``requires`` expressions involving substitution failures in C++ concepts. (#GH176402)
 - Fixed an incorrect template argument deduction when matching packs of template
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index aa72cb8fa2895..4306e32104e9b 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -1459,6 +1459,11 @@ QualType Sema::CheckNonTypeTemplateParameterType(QualType T,
     return QualType();
   }
 
+  if (T->isBlockPointerType()) {
+    Diag(Loc, diag::err_template_nontype_parm_bad_type) << T;
+    return QualType();
+  }
+
   // C++ [temp.param]p4:
   //
   // A non-type template-parameter shall have one of the following
diff --git a/clang/test/SemaCXX/blocks.cpp b/clang/test/SemaCXX/blocks.cpp
index 997ac2b5721df..67ac7d42f52c9 100644
--- a/clang/test/SemaCXX/blocks.cpp
+++ b/clang/test/SemaCXX/blocks.cpp
@@ -163,3 +163,7 @@ void static_data_member() {
     };
   };
 }
+
+namespace gh189247 {
+  template<void (^)()> struct A; // expected-error {{a non-type template parameter cannot have type 'void (^)()'}}
+}