[Clang] fix generic lambda inside requires-clause of friend function template (#99813)

fixes #98258

The cause is that the assertion "Nothing should reference a value below
the actual template depth" is incorrect since we can have a generic
lambda inside requires-clause of friend function template, and the
generic lambda can reference to values with greater template depth.

---------

Co-authored-by: cor3ntin <[email protected]>

Author: Backl1ght

clang/docs/ReleaseNotes.rst

@@ -290,6 +290,8 @@ Bug Fixes to C++ Support
 - Clang now properly handles the order of attributes in `extern` blocks. (#GH101990).
 - Fixed an assertion failure by preventing null explicit object arguments from being deduced. (#GH102025).
 - Correctly check constraints of explicit instantiations of member functions. (#GH46029)
+- Fixed an assertion failure about a constraint of a friend function template references to a value with greater
+  template depth than the friend function template. (#GH98258)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaTemplate.cpp

@@ -1667,10 +1667,7 @@ class ConstraintRefersToContainingTemplateChecker
   }
 
   void CheckNonTypeTemplateParmDecl(NonTypeTemplateParmDecl *D) {
-    assert(D->getDepth() <= TemplateDepth &&
-           "Nothing should reference a value below the actual template depth, "
-           "depth is likely wrong");
-    if (D->getDepth() != TemplateDepth)
+    if (D->getDepth() < TemplateDepth)
       Result = true;
 
     // Necessary because the type of the NTTP might be what refers to the parent
@@ -1694,10 +1691,7 @@ class ConstraintRefersToContainingTemplateChecker
   using inherited::TransformTemplateTypeParmType;
   QualType TransformTemplateTypeParmType(TypeLocBuilder &TLB,
                                          TemplateTypeParmTypeLoc TL, bool) {
-    assert(TL.getDecl()->getDepth() <= TemplateDepth &&
-           "Nothing should reference a value below the actual template depth, "
-           "depth is likely wrong");
-    if (TL.getDecl()->getDepth() != TemplateDepth)
+    if (TL.getDecl()->getDepth() < TemplateDepth)
       Result = true;
     return inherited::TransformTemplateTypeParmType(
         TLB, TL,

clang/test/SemaTemplate/concepts-friends.cpp

@@ -504,3 +504,24 @@ template struct Z<int>;
 Y y(1);
 
 }
+
+namespace GH98258 {
+
+struct S {
+  template <typename U>
+  friend void f() requires requires { []<typename V>(V){}; } {
+    return;
+  }
+
+  template <typename U>
+  friend void f2() requires requires { [](auto){}; } {
+    return;
+  }
+
+  template <typename U>
+  friend void f3() requires requires { []<int X>(){ return X; }; } {
+    return;
+  }
+};
+
+}