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

Author: huqizhi

clang/docs/ReleaseNotes.rst

@@ -376,6 +376,8 @@ Bug Fixes to C++ Support
 - Fixed a crash in constant evaluation when trying to access a
   captured ``this`` pointer in a lambda with an explicit object parameter.
   Fixes (#GH80997)
+- Fix an issue where missing set friend declaration in template class instantiation.
+  Fixes (#GH84368).
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -1727,6 +1727,7 @@ Decl *TemplateDeclInstantiator::VisitClassTemplateDecl(ClassTemplateDecl *D) {
     assert(!Owner->isDependentContext());
     Inst->setLexicalDeclContext(Owner);
     RecordInst->setLexicalDeclContext(Owner);
+    Inst->setObjectOfFriendDecl();
 
     if (PrevClassTemplate) {
       Inst->setCommonPtr(PrevClassTemplate->getCommonPtr());

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;