[clang] [clang] Handle invalid template template arguments in partial ordering (PR #233138)

[Hrólf Kraki via cfe-commits]

https://github.com/Serosh-commits updated https://github.com/llvm/llvm-project/pull/233138

>From cb0947634c41a24b761863b47be410467ef8e6c4 Mon Sep 17 00:00:00 2001
From: Serosh-commits <janmejayapanda400 at gmail.com>
Date: Sun, 18 Oct 2026 02:59:23 +0530
Subject: [PATCH 1/2] [clang] Handle invalid template template arguments in
 partial ordering

---
 clang/lib/Sema/SemaTemplateDeduction.cpp | 6 ++----
 clang/test/SemaTemplate/gh227649.cpp     | 6 ++++++
 2 files changed, 8 insertions(+), 4 deletions(-)
 create mode 100644 clang/test/SemaTemplate/gh227649.cpp

diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 1544fd56b82ae2..651114329d4e9e 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -6609,11 +6609,9 @@ bool Sema::isTemplateTemplateParameterAtLeastAsSpecializedAs(
   case TemplateDeductionResult::Success:
     return true;
 
-  // It doesn't seem possible to get a non-deduced mismatch when partial
-  // ordering TTPs, except with an invalid template parameter list which has
-  // a parameter after a pack.
+  // An invalid template parameter list can produce a non-deduced mismatch
+  // while finishing the deduction.
   case TemplateDeductionResult::NonDeducedMismatch:
-    assert(PArg->isInvalidDecl() && "Unexpected NonDeducedMismatch");
     return false;
 
   // Substitution failures should have already been diagnosed.
diff --git a/clang/test/SemaTemplate/gh227649.cpp b/clang/test/SemaTemplate/gh227649.cpp
new file mode 100644
index 00000000000000..02784971cb6907
--- /dev/null
+++ b/clang/test/SemaTemplate/gh227649.cpp
@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -fsyntax-only %s 2>&1 | FileCheck %s
+// CHECK: error: use of undeclared identifier 'foo'
+
+template <template <decltype(foo())> typename> struct S {};
+template <int &p> struct P;
+S<P> s;

>From c667e4ad3f25ca1b7dd1724eb44237f8a36aa015 Mon Sep 17 00:00:00 2001
From: Serosh-commits <janmejayapanda400 at gmail.com>
Date: Sun, 18 Oct 2026 02:59:23 +0530
Subject: [PATCH 2/2] address review

---
 clang/lib/Sema/SemaTemplate.cpp          | 4 ++++
 clang/lib/Sema/SemaTemplateDeduction.cpp | 6 ++++--
 clang/test/SemaTemplate/gh227649.cpp     | 5 ++---
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 5667cf53fee0b5..74d064ced4d8c0 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -1595,6 +1595,8 @@ NamedDecl *Sema::ActOnNonTypeTemplateParameter(Scope *S, Declarator &D,
   if (T.isNull()) {
     T = Context.IntTy; // Recover with an 'int' type.
     Invalid = true;
+  } else if (T->containsErrors()) {
+    Invalid = true;
   }
 
   CheckFunctionOrTemplateParamDeclarator(S, D);
@@ -2447,6 +2449,8 @@ bool Sema::CheckTemplateParameterList(TemplateParameterList *NewParams,
   for (TemplateParameterList::iterator NewParam = NewParams->begin(),
                                     NewParamEnd = NewParams->end();
        NewParam != NewParamEnd; ++NewParam) {
+    Invalid |= (*NewParam)->isInvalidDecl();
+
     // Whether we've seen a duplicate default argument in the same translation
     // unit.
     bool RedundantDefaultArg = false;
diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 651114329d4e9e..1544fd56b82ae2 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -6609,9 +6609,11 @@ bool Sema::isTemplateTemplateParameterAtLeastAsSpecializedAs(
   case TemplateDeductionResult::Success:
     return true;
 
-  // An invalid template parameter list can produce a non-deduced mismatch
-  // while finishing the deduction.
+  // It doesn't seem possible to get a non-deduced mismatch when partial
+  // ordering TTPs, except with an invalid template parameter list which has
+  // a parameter after a pack.
   case TemplateDeductionResult::NonDeducedMismatch:
+    assert(PArg->isInvalidDecl() && "Unexpected NonDeducedMismatch");
     return false;
 
   // Substitution failures should have already been diagnosed.
diff --git a/clang/test/SemaTemplate/gh227649.cpp b/clang/test/SemaTemplate/gh227649.cpp
index 02784971cb6907..730e343bced319 100644
--- a/clang/test/SemaTemplate/gh227649.cpp
+++ b/clang/test/SemaTemplate/gh227649.cpp
@@ -1,6 +1,5 @@
-// RUN: %clang_cc1 -fsyntax-only %s 2>&1 | FileCheck %s
-// CHECK: error: use of undeclared identifier 'foo'
+// RUN: %clang_cc1 -fsyntax-only -verify %s
 
-template <template <decltype(foo())> typename> struct S {};
+template <template <decltype(foo())> typename> struct S {}; // expected-error {{use of undeclared identifier 'foo'}}
 template <int &p> struct P;
 S<P> s;