llvm · HamzaHassanain · Jan 3, 2026 · Jan 3, 2026 · Jan 3, 2026 · Jan 3, 2026
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
@@ -623,6 +623,10 @@ Bug Fixes to C++ Support
 - Fix the result of ``__is_pointer_interconvertible_base_of`` when arguments are qualified and passed via template parameters. (#GH135273)
 - Fixed a crash when evaluating nested requirements in requires-expressions that reference invented parameters. (#GH166325)
 - Fixed a crash when standard comparison categories (e.g. ``std::partial_ordering``) are defined with incorrect static member types. (#GH170015) (#GH56571)
+- Fixed a crash where Clang would attempt to generate code for a static data 
+  member declared with an alias template without template arguments. 
+  Clang now correctly diagnoses this as an undeduced type and rejects 
+  the declaration. (#GH173349)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
@@ -14333,7 +14333,7 @@ void Sema::ActOnUninitializedDecl(Decl *RealDecl) {
       return;
     }
 
-    if (Type->isUndeducedType() &&
+    if (Type->getContainedDeducedType() &&
         DeduceVariableDeclarationType(Var, false, nullptr))
       return;
 

diff --git a/clang/test/SemaCXX/alias-template.cpp b/clang/test/SemaCXX/alias-template.cpp
@@ -1,5 +1,7 @@
 // RUN: %clang_cc1 -verify -std=c++14 -fcxx-exceptions %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++20 %s
 
+#if __cplusplus < 202002L
 namespace RedeclAliasTypedef {
   template<typename U> using T = int;
   template<typename U> using T = int;
@@ -198,3 +200,18 @@ int g = sfinae_me<int>(); // expected-error{{no matching function for call to 's
 namespace NullExceptionDecl {
 template<int... I> auto get = []() { try { } catch(...) {}; return I; }; // expected-error{{initializer contains unexpanded parameter pack 'I'}}
 }
+#endif
+
+#if __cplusplus >= 202002L
+namespace PR174281 {
+template <class T>
+struct A {
+  template <class U>
+  using E = U; // expected-note {{template is declared here}}
+  static E u2 = 0; // expected-error {{alias template 'E' requires template arguments; argument deduction only allowed for class templates or alias templates}}
+  static E u; // expected-error {{declaration of variable 'u' with deduced type 'E' requires an initializer}}
+};
+
+decltype(A<int>::u) a; // expected-note {{in instantiation of template class 'PR174281::A<int>' requested here}}
+}
+#endif
-Original file line number
+Diff line change
@@ Expand Up / @@ -14333,7 +14333,7 @@ void Sema::ActOnUninitializedDecl(Decl *RealDecl) { @@
           return;
         }
-        if (Type->isUndeducedType() &&
+        if (Type->getContainedDeducedType() &&
             DeduceVariableDeclarationType(Var, false, nullptr))
           return;
@@ Expand Down @@