Address review comments.

Author: hokein

clang/lib/Sema/SemaTemplate.cpp

@@ -2779,7 +2779,7 @@ Expr *
 buildAssociatedConstraints(Sema &SemaRef, FunctionTemplateDecl *F,
                            TypeAliasTemplateDecl *AliasTemplate,
                            ArrayRef<DeducedTemplateArgument> DeduceResults,
-                           unsigned UndeducedTemplateParameterStartIndex,
+                           unsigned FirstUndeducedParamIdx,
                            Expr *IsDeducible) {
   Expr *RC = F->getTemplateParameters()->getRequiresClause();
   if (!RC)
@@ -2841,16 +2841,16 @@ buildAssociatedConstraints(Sema &SemaRef, FunctionTemplateDecl *F,
   for (unsigned Index = 0; Index < DeduceResults.size(); ++Index) {
     const auto &D = DeduceResults[Index];
     if (D.isNull()) { // non-deduced template parameters of f
-      auto TP = F->getTemplateParameters()->getParam(Index);
+      NamedDecl* TP = F->getTemplateParameters()->getParam(Index);
       MultiLevelTemplateArgumentList Args;
       Args.setKind(TemplateSubstitutionKind::Rewrite);
       Args.addOuterTemplateArguments(TemplateArgsForBuildingRC);
       // Rebuild the template parameter with updated depth and index.
       NamedDecl *NewParam = transformTemplateParameter(
           SemaRef, F->getDeclContext(), TP, Args,
-          /*NewIndex=*/UndeducedTemplateParameterStartIndex++,
+          /*NewIndex=*/FirstUndeducedParamIdx,
           getTemplateParameterDepth(TP) + AdjustDepth);
-
+      FirstUndeducedParamIdx += 1;
       assert(TemplateArgsForBuildingRC[Index].isNull());
       TemplateArgsForBuildingRC[Index] = Context.getCanonicalTemplateArgument(
           Context.getInjectedTemplateArg(NewParam));
@@ -2871,11 +2871,9 @@ buildAssociatedConstraints(Sema &SemaRef, FunctionTemplateDecl *F,
   MultiLevelTemplateArgumentList ArgsForBuildingRC;
   ArgsForBuildingRC.setKind(clang::TemplateSubstitutionKind::Rewrite);
   ArgsForBuildingRC.addOuterTemplateArguments(TemplateArgsForBuildingRC);
-  // For 2), if the underlying function template F is nested in a class template
-  // (either instantiated from an explicitly-written deduction guide, or
-  // synthesized from a constructor), we need the entire template argument list,
-  // as the constraint AST in the require-clause of F remains completely
-  // uninstantiated.
+  // For 2), if the underlying deduction guide F is nested in a class template,
+  // we need the entire template argument list, as the constraint AST in the
+  // require-clause of F remains completely uninstantiated.
   //
   // For example:
   //   template <typename T> // depth 0
@@ -2898,6 +2896,11 @@ buildAssociatedConstraints(Sema &SemaRef, FunctionTemplateDecl *F,
   // We add the outer template arguments which is [int] to the multi-level arg
   // list to ensure that the occurrence U in `C<U>` will be replaced with int
   // during the substitution.
+  //
+  // NOTE: The underlying deduction guide F is instantiated -- either from an
+  // explicitly-written deduction guide member, or from a constructor.
+  // getInstantiatedFromMemberTemplate() can only handle the former case, so we
+  // check the DeclContext kind.
   if (F->getLexicalDeclContext()->getDeclKind() ==
       clang::Decl::ClassTemplateSpecialization) {
     auto OuterLevelArgs = SemaRef.getTemplateInstantiationArgs(
@@ -3117,7 +3120,7 @@ BuildDeductionGuideForTypeAlias(Sema &SemaRef,
         Context.getInjectedTemplateArg(NewParam));
     TransformedDeducedAliasArgs[AliasTemplateParamIdx] = NewTemplateArgument;
   }
-  unsigned UndeducedTemplateParameterStartIndex = FPrimeTemplateParams.size();
+  unsigned FirstUndeducedParamIdx = FPrimeTemplateParams.size();
   //   ...followed by the template parameters of f that were not deduced
   //   (including their default template arguments)
   for (unsigned FTemplateParamIdx : NonDeducedTemplateParamsInFIndex) {
@@ -3188,7 +3191,7 @@ BuildDeductionGuideForTypeAlias(Sema &SemaRef,
         SemaRef, AliasTemplate, FPrime->getReturnType(), FPrimeTemplateParams);
     Expr *RequiresClause = buildAssociatedConstraints(
         SemaRef, F, AliasTemplate, DeduceResults,
-        UndeducedTemplateParameterStartIndex, IsDeducible);
+        FirstUndeducedParamIdx, IsDeducible);
 
     auto *FPrimeTemplateParamList = TemplateParameterList::Create(
         Context, AliasTemplate->getTemplateParameters()->getTemplateLoc(),

clang/test/AST/ast-dump-ctad-alias.cpp

@@ -58,7 +58,9 @@ template <typename T0>
 struct Out3 {
   template<class T1, typename T2>
   struct Foo {
-    // Deduction guide: Foo(T1, T2, V) -> Foo<T1, T2, V>;
+    // Deduction guide:
+    //   template <typename T1, typename T2, typename V>
+    //   Foo(V, T1) -> Foo<T1, T2>;
     template<class V> requires Concept<T0, V> // V in require clause of Foo deduction guide: depth 1, index: 2
     Foo(V, T1);
   };