release/21.x: [clang] Avoid inheriting [[noreturn]] in explicit function template specializations (#150003)

[llvmbot]

Backport 22fef00

Requested by: @mstorsjo

[llvmbot]

@alexfh What do you think about merging this PR to the release branch?

[llvmbot]

@llvm/pr-subscribers-clang

Author: None (llvmbot)

Changes

Backport 22fef00

Requested by: @mstorsjo

---

Full diff: https://github.com/llvm/llvm-project/pull/151752.diff

3 Files Affected:

• (modified) clang/lib/Sema/SemaDecl.cpp (+8)
• (modified) clang/lib/Sema/SemaDeclAttr.cpp (+7)
• (modified) clang/test/SemaCXX/wreturn-always-throws.cpp (+20-1)

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 eff5f9568236a..a7897bdfe6e0f 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -1970,6 +1970,13 @@ void clang::inferNoReturnAttr(Sema &S, const Decl *D) {
   if (!FD)
     return;
 
+  // Skip explicit specializations here as they may have
+  // a user-provided definition that may deliberately differ from the primary
+  // template. If an explicit specialization truly never returns, the user
+  // should explicitly mark it with [[noreturn]].
+  if (FD->getTemplateSpecializationKind() == TSK_ExplicitSpecialization)
+    return;
+
   auto *NonConstFD = const_cast<FunctionDecl *>(FD);
   DiagnosticsEngine &Diags = S.getDiagnostics();
   if (Diags.isIgnored(diag::warn_falloff_nonvoid, FD->getLocation()) &&
diff --git a/clang/test/SemaCXX/wreturn-always-throws.cpp b/clang/test/SemaCXX/wreturn-always-throws.cpp
index addcadd1183dc..df7689f7063cc 100644
--- a/clang/test/SemaCXX/wreturn-always-throws.cpp
+++ b/clang/test/SemaCXX/wreturn-always-throws.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -fcxx-exceptions -fexceptions -Wreturn-type -verify %s
+// RUN: %clang_cc1 -fsyntax-only -fcxx-exceptions -fexceptions -Wreturn-type -Winvalid-noreturn -verify %s
 // expected-no-diagnostics
 
 namespace std {
@@ -44,3 +44,22 @@ 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();
+  void g();
+};
+
+template<typename T>
+void S<T>::f() { throw 0; } 
+template<>
+void S<int>::f() {}
+
+template<typename T> 
+void S<T>::g() {}  
+template<> 
+void S<int>::g() { throw 0; }

[github-actions]

⚠️ We detected that you are using a GitHub private e-mail address to contribute to the repo.
Please turn off Keep my email addresses private setting in your account.
See LLVM Developer Policy and LLVM Discourse for more information.

[cor3ntin]

LGTM
but main could be improved with an nfc commit
#150003 (review)

[github-actions]

@mstorsjo (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR.