[Clang] Drop unrelated template arguments in substituted parameter mapping

[zyn0217]

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

This is a trunk regression.

Fixes #163057

[shafik]

The capitalization change added a lot of noise, obscuring the substantive change.

[llvmbot]

@llvm/pr-subscribers-hlsl

@llvm/pr-subscribers-clang

Author: Younan Zhang (zyn0217)

Changes

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

This is a trunk regression.

Fixes #163057

---

Full diff: https://github.com/llvm/llvm-project/pull/163221.diff

3 Files Affected:

• (modified) clang/include/clang/Sema/Template.h (+2-2)
• (modified) clang/lib/Sema/SemaConcept.cpp (+20-19)
• (modified) clang/test/SemaTemplate/concepts.cpp (+25)

diff --git a/clang/include/clang/Sema/Template.h b/clang/include/clang/Sema/Template.h
index 60c7d275f1aaf..4acb3a84c4f38 100644
--- a/clang/include/clang/Sema/Template.h
+++ b/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 are not needed to be
+    /// resugared later.
     void addOuterTemplateArguments(Decl *AssociatedDecl, ArgList Args,
                                    bool Final) {
       assert(!NumRetainedOuterLevels &&
diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index 7c44efd7b9c1c..77ccf6827b021 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -565,7 +565,7 @@ std::optional<MultiLevelTemplateArgumentList>
 ConstraintSatisfactionChecker::SubstitutionInTemplateArguments(
     const NormalizedConstraintWithParamMapping &Constraint,
     MultiLevelTemplateArgumentList MLTAL,
-    llvm::SmallVector<TemplateArgument> &SubstitutedOuterMost) {
+    llvm::SmallVector<TemplateArgument> &SubstitutedOutermost) {
 
   if (!Constraint.hasParameterMapping())
     return std::move(MLTAL);
@@ -606,37 +606,38 @@ 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;
     if (Used[I])
       Arg = CTAI.SugaredConverted[MappedIndex++];
-    if (I < SubstitutedOuterMost.size()) {
-      SubstitutedOuterMost[I] = Arg;
+    if (I < SubstitutedOutermost.size()) {
+      SubstitutedOutermost[I] = Arg;
       Offset = I + 1;
     } else {
-      SubstitutedOuterMost.push_back(Arg);
-      Offset = SubstitutedOuterMost.size();
+      SubstitutedOutermost.push_back(Arg);
+      Offset = SubstitutedOutermost.size();
     }
   }
-  if (Offset < SubstitutedOuterMost.size())
-    SubstitutedOuterMost.erase(SubstitutedOuterMost.begin() + Offset);
+  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(
     const AtomicConstraint &Constraint,
     const MultiLevelTemplateArgumentList &MLTAL) {
 
-  llvm::SmallVector<TemplateArgument> SubstitutedOuterMost;
+  llvm::SmallVector<TemplateArgument> SubstitutedOutermost;
   std::optional<MultiLevelTemplateArgumentList> SubstitutedArgs =
-      SubstitutionInTemplateArguments(Constraint, MLTAL, SubstitutedOuterMost);
+      SubstitutionInTemplateArguments(Constraint, MLTAL, SubstitutedOutermost);
   if (!SubstitutedArgs) {
     Satisfaction.IsSatisfied = false;
     return ExprEmpty();
@@ -784,13 +785,13 @@ ExprResult ConstraintSatisfactionChecker::EvaluateSlow(
                      FoldExpandedConstraint::FoldOperatorKind::And;
   unsigned EffectiveDetailEndIndex = Satisfaction.Details.size();
 
-  llvm::SmallVector<TemplateArgument> SubstitutedOuterMost;
+  llvm::SmallVector<TemplateArgument> SubstitutedOutermost;
   // FIXME: Is PackSubstitutionIndex correct?
   llvm::SaveAndRestore _(PackSubstitutionIndex, S.ArgPackSubstIndex);
   std::optional<MultiLevelTemplateArgumentList> SubstitutedArgs =
       SubstitutionInTemplateArguments(
           static_cast<const NormalizedConstraintWithParamMapping &>(Constraint),
-          MLTAL, SubstitutedOuterMost);
+          MLTAL, SubstitutedOutermost);
   if (!SubstitutedArgs) {
     Satisfaction.IsSatisfied = false;
     return ExprError();
@@ -878,9 +879,9 @@ ExprResult ConstraintSatisfactionChecker::EvaluateSlow(
     const MultiLevelTemplateArgumentList &MLTAL, unsigned Size) {
   const ConceptReference *ConceptId = Constraint.getConceptId();
 
-  llvm::SmallVector<TemplateArgument> SubstitutedOuterMost;
+  llvm::SmallVector<TemplateArgument> SubstitutedOutermost;
   std::optional<MultiLevelTemplateArgumentList> SubstitutedArgs =
-      SubstitutionInTemplateArguments(Constraint, MLTAL, SubstitutedOuterMost);
+      SubstitutionInTemplateArguments(Constraint, MLTAL, SubstitutedOutermost);
 
   if (!SubstitutedArgs) {
     Satisfaction.IsSatisfied = false;
diff --git a/clang/test/SemaTemplate/concepts.cpp b/clang/test/SemaTemplate/concepts.cpp
index ee2bb8de66079..c31c961892f4a 100644
--- a/clang/test/SemaTemplate/concepts.cpp
+++ b/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 {

[mizvekov]

What is going on with the unit test failure?
Looks unrelated, but I am not sure.

[zyn0217]

@mizvekov it's #163277 which has been reverted. Though I haven't rerun CI yet.