[Clang][Sema] Fix a bug on type constraint checking

[jcsxky]

Try to fix #84368
When visiting class members in TemplateDeclInstantiator::VisitClassTemplateDecl during Sema::InstantiateClass, we miss to set attribute of friend declaration if it is(isFriend is true). This will lead to Sema::AreConstraintExpressionsEqual return false when invoked in MatchTemplateParameterKind. Because it makes Sema::getTemplateInstantiationArgs returns incorrect template argument(MultiLevelTemplateArgumentList). When we handle CXXRecordDecl In Sema::getTemplateInstantiationArgs, friend declaration(its parent context is FileContext) makes us to choose LexicalDeclContext not DeclContext and this is what we want.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Qizhi Hu (jcsxky)

Changes

Try to fix #84368
[temp.friend]p1:
Similarly, each specialization of the task class template has the class template
specialization task<int> as a friend, and has all specializations of the class template frd as friends.

---

Full diff: https://github.com/llvm/llvm-project/pull/84671.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+2)
• (modified) clang/lib/Sema/SemaTemplateInstantiateDecl.cpp (+1)
• (added) clang/test/Sema/PR84368.cpp (+16)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 3b89d5a8720785..b32e739288dbc5 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -259,6 +259,8 @@ Bug Fixes in This Version
   operator.
   Fixes (#GH83267).
 
+- Fix a bug on type constraint checking (#GH84368). 
+
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 20c2c93ac9c7b4..765c5bc689ae1e 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -1698,6 +1698,7 @@ Decl *TemplateDeclInstantiator::VisitClassTemplateDecl(ClassTemplateDecl *D) {
     assert(!Owner->isDependentContext());
     Inst->setLexicalDeclContext(Owner);
     RecordInst->setLexicalDeclContext(Owner);
+    Inst->setObjectOfFriendDecl();
 
     if (PrevClassTemplate) {
       Inst->setCommonPtr(PrevClassTemplate->getCommonPtr());
diff --git a/clang/test/Sema/PR84368.cpp b/clang/test/Sema/PR84368.cpp
new file mode 100644
index 00000000000000..073530ffd8abea
--- /dev/null
+++ b/clang/test/Sema/PR84368.cpp
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -std=c++20 -verify %s
+// RUN: %clang_cc1 -std=c++23 -verify %s
+// expected-no-diagnostics
+
+template<class T> concept IsOk = requires() { typename T::Float; };
+
+template<IsOk T> struct Thing;
+
+template<IsOk T> struct Foobar {
+	template<int> struct Inner {
+		template<IsOk T2> friend struct Thing;
+	};
+};
+
+struct MyType { using Float=float; };
+Foobar<MyType>::Inner<0> foobar;

[erichkeane]

The commit message and release note needs to be MUCH more detailed. Else I think this looks like an acceptable patch.

[jcsxky]

The commit message and release note needs to be MUCH more detailed. Else I think this looks like an acceptable patch.

Thanks for you remind! I have updated commit message and release note to make it more clear.

[erichkeane]

Indenting here doesn't match our clang-format rules. Please fix that.

[jcsxky]

Fixed.