[clang] [Clang] Diagnose unexpanded packs for NTTP type constraints (PR #121296)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 created https://github.com/llvm/llvm-project/pull/121296

Otherwise, the invalid unexpanded type would be passed to getAutoType and lead to a crash.

Fixes https://github.com/llvm/llvm-project/issues/88866

>From 102e031cae56c130f48f08bcb316b6f451facf49 Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109 at gmail.com>
Date: Sun, 29 Dec 2024 23:13:52 +0800
Subject: [PATCH] [Clang] Diagnose unexpanded packs for NTTP type constraints

---
 clang/docs/ReleaseNotes.rst             |  1 +
 clang/lib/Sema/SemaTemplate.cpp         | 12 +++++--
 clang/test/SemaCXX/cxx2c-fold-exprs.cpp | 43 +++++++++++++++++++++++++
 3 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 8b984ecaefecaf..78ae4c8cab3a9e 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -885,6 +885,7 @@ Bug Fixes to C++ Support
 - Fixed recognition of ``std::initializer_list`` when it's surrounded with ``extern "C++"`` and exported
   out of a module (which is the case e.g. in MSVC's implementation of ``std`` module). (#GH118218)
 - Fixed a pack expansion issue in checking unexpanded parameter sizes. (#GH17042)
+- Clang now identifies unexpanded parameter packs within the type constraint on a non-type template parameter. (#GH88866)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 5e7a3c8484c88f..eac184d468ce9a 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -1530,9 +1530,17 @@ NamedDecl *Sema::ActOnNonTypeTemplateParameter(Scope *S, Declarator &D,
   Param->setAccess(AS_public);
 
   if (AutoTypeLoc TL = TInfo->getTypeLoc().getContainedAutoTypeLoc())
-    if (TL.isConstrained())
-      if (AttachTypeConstraint(TL, Param, Param, D.getEllipsisLoc()))
+    if (TL.isConstrained()) {
+      if (const ASTTemplateArgumentListInfo *ArgumentList =
+              TL.getConceptReference()->getTemplateArgsAsWritten())
+        for (const TemplateArgumentLoc &Loc : ArgumentList->arguments()) {
+          Invalid |= DiagnoseUnexpandedParameterPack(
+              Loc, UnexpandedParameterPackContext::UPPC_TypeConstraint);
+        }
+      if (!Invalid &&
+          AttachTypeConstraint(TL, Param, Param, D.getEllipsisLoc()))
         Invalid = true;
+    }
 
   if (Invalid)
     Param->setInvalidDecl();
diff --git a/clang/test/SemaCXX/cxx2c-fold-exprs.cpp b/clang/test/SemaCXX/cxx2c-fold-exprs.cpp
index 0674135aac483f..00236a8a839135 100644
--- a/clang/test/SemaCXX/cxx2c-fold-exprs.cpp
+++ b/clang/test/SemaCXX/cxx2c-fold-exprs.cpp
@@ -305,3 +305,46 @@ static_assert(__is_same_as(_Three_way_comparison_result_with_tuple_like<tuple<in
 static_assert(__is_same_as(_Three_way_comparison_result_with_tuple_like<tuple<int>, 0>::type, long));
 
 }
+
+namespace GH88866 {
+
+template <typename...Ts> struct index_by;
+
+template <typename T, typename Indices>
+concept InitFunc = true;
+
+namespace Invalid {
+
+template <typename Indices, InitFunc<Indices> auto... init>
+struct LazyLitMatrix;
+
+template <
+    typename...Indices,
+    InitFunc<index_by<Indices>> auto... init
+    // expected-error at -1 {{type constraint contains unexpanded parameter pack 'Indices'}}
+>
+struct LazyLitMatrix<index_by<Indices...>, init...> {
+};
+
+static_assert(
+    !__is_same(LazyLitMatrix<index_by<int, char>, 42, 43>, LazyLitMatrix<index_by<int, char>, 42, 43>));
+// expected-error at -1 {{static assertion failed}}
+}
+
+namespace Valid {
+
+template <typename Indices, InitFunc<Indices> auto... init>
+struct LazyLitMatrix;
+
+template <
+    typename...Indices,
+    InitFunc<index_by<Indices...>> auto... init
+>
+struct LazyLitMatrix<index_by<Indices...>, init...> {
+};
+
+static_assert(__is_same(LazyLitMatrix<index_by<int, char>, 42, 43>, 
+                        LazyLitMatrix<index_by<int, char>, 42, 43>));
+}
+
+}