[clang] [clang] CTAD: Track template template type parameters that referenced in (PR #85405)

[Haojian Wu via cfe-commits]

https://github.com/hokein updated https://github.com/llvm/llvm-project/pull/85405

>From 2d3aee2e763e3e4970d97406e59df66e5861d5ba Mon Sep 17 00:00:00 2001
From: Haojian Wu <hokein.wu at gmail.com>
Date: Fri, 15 Mar 2024 15:09:10 +0100
Subject: [PATCH 1/2] [clang] CTAD: Track template template type parameters
 that referenced in the template arguments of the RHS.

Fixes https://github.com/llvm/llvm-project/issues/85385.

The Finder was missing for this case, for the crash test, the template
parameter TTP was incorrectly considered as not referenced/appeared in
the template arguments of the right hand side of the alias template
decl, thus the synthesized deduction decl doesn't contain this TTP in
the template parameter list, but we have references in the declaration,
thus it caused crashes.
---
 clang/lib/Sema/SemaTemplate.cpp              |  6 ++++++
 clang/test/SemaCXX/cxx20-ctad-type-alias.cpp | 16 ++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 51e8db2dfbaac8..27714066d2748b 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -2696,6 +2696,12 @@ SmallVector<unsigned> TemplateParamsReferencedInTemplateArgumentList(
       return true;
     }
 
+    bool TraverseTemplateName(TemplateName Template) {
+      if (auto *TD = Template.getAsTemplateDecl())
+        MarkAppeared(TD);
+      return RecursiveASTVisitor::TraverseTemplateName(Template);
+    }
+
     void MarkAppeared(NamedDecl *ND) {
       if (TemplateParams.contains(ND))
         ReferencedTemplateParams.insert(ND);
diff --git a/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp b/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp
index 3ce26c8fcd984e..7ada48b7e58f01 100644
--- a/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp
+++ b/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp
@@ -247,3 +247,19 @@ using Bar = Foo<U>; // expected-note {{could not match 'Foo<type-parameter-0-0>'
 
 Bar s = {1}; // expected-error {{no viable constructor or deduction guide for deduction of template arguments}}
 } // namespace test18
+
+// GH85385
+namespace test19 {
+template <template <typename> typename T>
+struct K {};
+
+template <typename U>
+class Foo {};
+
+// Verify that template template type parameter TTP is referenced/used in the
+// template arguments of the RHS.
+template <template<typename> typename TTP>
+using Bar = Foo<K<TTP>>; // expected-note {{candidate template ignored: could not match 'Foo<K<>>' against 'int'}}
+
+Bar s = 1; // expected-error {{no viable constructor or deduction guide for deduction of template arguments of}}
+}

>From 35153db8d8160b9fb7f821b95c7191d1045d5fbf Mon Sep 17 00:00:00 2001
From: Haojian Wu <hokein.wu at gmail.com>
Date: Wed, 27 Mar 2024 10:50:24 +0100
Subject: [PATCH 2/2] Add a testcase to cover the valid code.

---
 clang/test/SemaCXX/cxx20-ctad-type-alias.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp b/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp
index 7ada48b7e58f01..1c5967777f3255 100644
--- a/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp
+++ b/clang/test/SemaCXX/cxx20-ctad-type-alias.cpp
@@ -261,5 +261,9 @@ class Foo {};
 template <template<typename> typename TTP>
 using Bar = Foo<K<TTP>>; // expected-note {{candidate template ignored: could not match 'Foo<K<>>' against 'int'}}
 
+template <class T>
+class Container {};
+Bar t = Foo<K<Container>>();
+
 Bar s = 1; // expected-error {{no viable constructor or deduction guide for deduction of template arguments of}}
 }