[clang] 4cc0bae - [clang] fix getReplacedTemplateParameter for partial specialziations (#162955)

[via cfe-commits]

Author: Matheus Izvekov
Date: 2025-10-10T23:00:36-03:00
New Revision: 4cc0bae159e56dc02145f9154005dc1eb9ed1fd7

URL: https://github.com/llvm/llvm-project/commit/4cc0bae159e56dc02145f9154005dc1eb9ed1fd7
DIFF: https://github.com/llvm/llvm-project/commit/4cc0bae159e56dc02145f9154005dc1eb9ed1fd7.diff

LOG: [clang] fix getReplacedTemplateParameter for partial specialziations (#162955)

The template argument returned should be relative to the partial
specialization, which would correspond to the partial template parameter
list.

Unfortunately we don't save this anywhere in the AST, and would
otherwise need to deduce them again.

Simply avoid providing this argument for now, until we make it
available.

This fixes regressions which were never released, so there are no
release notes.

Fixes #162770
Fixes #162855

Added: 
    

Modified: 
    clang/lib/AST/DeclTemplate.cpp
    clang/test/SemaTemplate/concepts.cpp
    clang/test/SemaTemplate/partial-spec-instantiate.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/AST/DeclTemplate.cpp b/clang/lib/AST/DeclTemplate.cpp
index c0be986824cff..2f7ae6d6cac63 100644
--- a/clang/lib/AST/DeclTemplate.cpp
+++ b/clang/lib/AST/DeclTemplate.cpp
@@ -1670,20 +1670,25 @@ clang::getReplacedTemplateParameter(Decl *D, unsigned Index) {
     auto P = CTSD->getSpecializedTemplateOrPartial();
     TemplateParameterList *TPL;
     if (const auto *CTPSD =
-            dyn_cast<ClassTemplatePartialSpecializationDecl *>(P))
+            dyn_cast<ClassTemplatePartialSpecializationDecl *>(P)) {
       TPL = CTPSD->getTemplateParameters();
-    else
-      TPL = cast<ClassTemplateDecl *>(P)->getTemplateParameters();
+      // FIXME: Obtain Args deduced for the partial specialization.
+      return {TPL->getParam(Index), {}};
+    }
+    TPL = cast<ClassTemplateDecl *>(P)->getTemplateParameters();
     return {TPL->getParam(Index), CTSD->getTemplateArgs()[Index]};
   }
   case Decl::Kind::VarTemplateSpecialization: {
     const auto *VTSD = cast<VarTemplateSpecializationDecl>(D);
     auto P = VTSD->getSpecializedTemplateOrPartial();
     TemplateParameterList *TPL;
-    if (const auto *VTPSD = dyn_cast<VarTemplatePartialSpecializationDecl *>(P))
+    if (const auto *VTPSD =
+            dyn_cast<VarTemplatePartialSpecializationDecl *>(P)) {
       TPL = VTPSD->getTemplateParameters();
-    else
-      TPL = cast<VarTemplateDecl *>(P)->getTemplateParameters();
+      // FIXME: Obtain Args deduced for the partial specialization.
+      return {TPL->getParam(Index), {}};
+    }
+    TPL = cast<VarTemplateDecl *>(P)->getTemplateParameters();
     return {TPL->getParam(Index), VTSD->getTemplateArgs()[Index]};
   }
   case Decl::Kind::ClassTemplatePartialSpecialization:

diff  --git a/clang/test/SemaTemplate/concepts.cpp b/clang/test/SemaTemplate/concepts.cpp
index 768af09afe9e2..1dbb9897f941f 100644
--- a/clang/test/SemaTemplate/concepts.cpp
+++ b/clang/test/SemaTemplate/concepts.cpp
@@ -1476,3 +1476,20 @@ static_assert( requires {{ &f } -> C;} ); // expected-error {{reference to overl
 // expected-error at -1 {{static assertion failed due to requirement 'requires { { &f() } -> C; }'}}
 
 }
+
+namespace GH162770 {
+  enum e {};
+  template<e> struct s {};
+
+  template<typename> struct specialized;
+  template<e x> struct specialized<s<x>> {
+    static auto make(auto) -> s<x>;
+  };
+
+  template<e x> struct check {
+    static constexpr auto m = requires { specialized<s<x>>::make(0); };
+  };
+
+  template<typename... Ts> auto comma = (..., Ts());
+  auto b = comma<check<e{}>>;
+} // namespace GH162770

diff  --git a/clang/test/SemaTemplate/partial-spec-instantiate.cpp b/clang/test/SemaTemplate/partial-spec-instantiate.cpp
index 0b84df69562e2..44b58008a1d33 100644
--- a/clang/test/SemaTemplate/partial-spec-instantiate.cpp
+++ b/clang/test/SemaTemplate/partial-spec-instantiate.cpp
@@ -152,3 +152,16 @@ namespace GH60778 {
     ClassTemplate<>::Nested<int> instantiation;
   }
 }
+#if __cplusplus >= 201103L
+namespace GH162855 {
+  template <class...> using A = int;
+  template <class, int> struct B;
+  template <class...> struct C;
+  template <template <class, int...> class TT, long... X>
+  struct C<TT<int, X...>> {
+    template <class... Y> using l = A<B<Y, X>...>;
+  };
+  template <class> struct D;
+  template struct C<D<int>>;
+} // namespace GH162855
+#endif