[clang] [Sema] Avoid attaching 'noreturn' attribute to explicit function temp… (PR #150003)

[Samarth Narang via cfe-commits]

https://github.com/snarang181 updated https://github.com/llvm/llvm-project/pull/150003

>From ff5dfd4fae47cd212a0882895396c0cb855e29a3 Mon Sep 17 00:00:00 2001
From: Samarth Narang <snarang at umass.edu>
Date: Tue, 22 Jul 2025 07:38:22 -0400
Subject: [PATCH 1/2] [Sema] Avoid attaching 'noreturn' attribute to explicit
 function template specializations

---
 clang/lib/Sema/SemaDecl.cpp     | 8 ++++++++
 clang/lib/Sema/SemaDeclAttr.cpp | 3 +++
 2 files changed, 11 insertions(+)

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 14403e65e8f42..bb412ef6788e7 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -3267,6 +3267,14 @@ void Sema::mergeDeclAttributes(NamedDecl *New, Decl *Old,
     if (isa<UsedAttr>(I) || isa<RetainAttr>(I))
       continue;
 
+    if (isa<InferredNoReturnAttr>(I)) {
+      if (auto *FD = dyn_cast<FunctionDecl>(New)) {
+        if (FD->getTemplateSpecializationKind() == TSK_ExplicitSpecialization)
+          continue; // Don't propagate inferred noreturn attributes to explicit
+                    // specializations.
+      }
+    }
+
     if (mergeDeclAttribute(*this, New, I, LocalAMK))
       foundAny = true;
   }
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 78f4804202ddc..a61d10c166578 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -1970,6 +1970,9 @@ void clang::inferNoReturnAttr(Sema &S, const Decl *D) {
   if (!FD)
     return;
 
+  if (FD->getTemplateSpecializationKind() == TSK_ExplicitSpecialization)
+    return; // Don't infer noreturn for explicit specializations.
+
   auto *NonConstFD = const_cast<FunctionDecl *>(FD);
   DiagnosticsEngine &Diags = S.getDiagnostics();
   if (Diags.isIgnored(diag::warn_falloff_nonvoid, FD->getLocation()) &&

>From eba957a9674942eae435b7693f7b6228b5ec63a6 Mon Sep 17 00:00:00 2001
From: Samarth Narang <snarang at umass.edu>
Date: Tue, 22 Jul 2025 09:13:20 -0400
Subject: [PATCH 2/2] Add LIT test

---
 clang/test/SemaCXX/wreturn-always-throws.cpp | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/clang/test/SemaCXX/wreturn-always-throws.cpp b/clang/test/SemaCXX/wreturn-always-throws.cpp
index addcadd1183dc..c307bc675c14b 100644
--- a/clang/test/SemaCXX/wreturn-always-throws.cpp
+++ b/clang/test/SemaCXX/wreturn-always-throws.cpp
@@ -44,3 +44,18 @@ void testTemplates() {
   throwErrorTemplate("ERROR");
   (void)ensureZeroTemplate(42);
 }
+
+// Ensure that explicit specialization of a member function does not inherit
+// the warning from the primary template.
+
+template<typename T>
+struct S {
+  void f();
+};
+
+template<typename T>
+void S<T>::f() { throw 0; } 
+template<>
+void S<int>::f() {} // expected-no-diagnostics
+
+