[Clang] Drop unrelated template arguments in substituted parameter mapping (#163221)

The unused template arguments living in different levels would confuse
the substitution otherwise.

This is a trunk regression, so no release note.

Fixes #163057

Author: zyn0217

clang/include/clang/Sema/Template.h

@@ -205,8 +205,8 @@ enum class TemplateSubstitutionKind : char {
 
     /// Add a new outmost level to the multi-level template argument
     /// list.
-    /// A 'Final' substitution means that Subst* nodes won't be built
-    /// for the replacements.
+    /// A 'Final' substitution means that these Args don't need to be
+    /// resugared later.
     void addOuterTemplateArguments(Decl *AssociatedDecl, ArgList Args,
                                    bool Final) {
       assert(!NumRetainedOuterLevels &&

clang/lib/Sema/SemaConcept.cpp

@@ -606,10 +606,9 @@ ConstraintSatisfactionChecker::SubstitutionInTemplateArguments(
       Constraint.mappingOccurenceList();
   // The empty MLTAL situation should only occur when evaluating non-dependent
   // constraints.
-  if (!MLTAL.getNumSubstitutedLevels())
-    MLTAL.addOuterTemplateArguments(TD, {}, /*Final=*/false);
-  SubstitutedOuterMost =
-      llvm::to_vector_of<TemplateArgument>(MLTAL.getOutermost());
+  if (MLTAL.getNumSubstitutedLevels())
+    SubstitutedOuterMost =
+        llvm::to_vector_of<TemplateArgument>(MLTAL.getOutermost());
   unsigned Offset = 0;
   for (unsigned I = 0, MappedIndex = 0; I < Used.size(); I++) {
     TemplateArgument Arg;
@@ -627,8 +626,10 @@ ConstraintSatisfactionChecker::SubstitutionInTemplateArguments(
   if (Offset < SubstitutedOuterMost.size())
     SubstitutedOuterMost.erase(SubstitutedOuterMost.begin() + Offset);
 
-  MLTAL.replaceOutermostTemplateArguments(TD, SubstitutedOuterMost);
-  return std::move(MLTAL);
+  MultiLevelTemplateArgumentList SubstitutedTemplateArgs;
+  SubstitutedTemplateArgs.addOuterTemplateArguments(TD, SubstitutedOuterMost,
+                                                    /*Final=*/false);
+  return std::move(SubstitutedTemplateArgs);
 }
 
 ExprResult ConstraintSatisfactionChecker::EvaluateSlow(

clang/test/SemaTemplate/concepts.cpp

@@ -1416,6 +1416,31 @@ concept IsEntitySpec =
 
 }
 
+namespace case8 {
+
+template <class T>
+struct type_identity {
+    using type = T;
+};
+
+template <typename Inner>
+struct Cat {};
+
+template <typename T>
+concept CatConcept = requires {
+    []<class Inner>(type_identity<Cat<Inner>>) {}(type_identity<T>{});
+};
+
+template <typename Dummy>
+struct Feeder {
+    template <CatConcept Dummy2>
+    void feed() noexcept {}
+};
+
+void main() { Feeder<int>{}.feed<Cat<int>>(); }
+
+}
+
 }
 
 namespace GH162125 {