[Clang][NFCI] Slightly refactor getTemplateInstantiationArgs()

clang/include/clang/Sema/Sema.h

@@ -13033,11 +13033,14 @@ class Sema final : public SemaBase {
   /// instantiation arguments.
   ///
   /// \param DC In the event we don't HAVE a declaration yet, we instead provide
-  ///  the decl context where it will be created.  In this case, the `Innermost`
-  ///  should likely be provided.  If ND is non-null, this is ignored.
+  ///  the decl context where it will be created.  In this case, the \p
+  ///  Innermost should likely be provided.  If \p ND is non-null and \p
+  ///  Innermost is NULL, this is ignored.
   ///
   /// \param Innermost if non-NULL, specifies a template argument list for the
-  /// template declaration passed as ND.
+  /// template declaration passed as \p ND. The next declaration context would
+  /// be switched to \p DC if present; otherwise, it would be the semantic
+  /// declaration context of \p ND.
   ///
   /// \param RelativeToPrimary true if we should get the template
   /// arguments relative to the primary template, even when we're
@@ -13053,6 +13056,9 @@ class Sema final : public SemaBase {
   /// ForConstraintInstantiation indicates we should continue looking when
   /// encountering a lambda generic call operator, and continue looking for
   /// arguments on an enclosing class template.
+  ///
+  /// \param SkipForSpecialization when specified, any template specializations
+  /// in a traversal would be ignored.
   MultiLevelTemplateArgumentList getTemplateInstantiationArgs(
       const NamedDecl *D, const DeclContext *DC = nullptr, bool Final = false,
       std::optional<ArrayRef<TemplateArgument>> Innermost = std::nullopt,

clang/lib/Sema/SemaConcept.cpp

@@ -1487,7 +1487,7 @@ substituteParameterMappings(Sema &S, NormalizedConstraint &N,
 static bool substituteParameterMappings(Sema &S, NormalizedConstraint &N,
                                         const ConceptSpecializationExpr *CSE) {
   MultiLevelTemplateArgumentList MLTAL = S.getTemplateInstantiationArgs(
-      CSE->getNamedConcept(), CSE->getNamedConcept()->getLexicalDeclContext(),
+      CSE->getNamedConcept(), CSE->getNamedConcept()->getDeclContext(),
       /*Final=*/false, CSE->getTemplateArguments(),
       /*RelativeToPrimary=*/true,
       /*Pattern=*/nullptr,

clang/lib/Sema/SemaTemplate.cpp

@@ -5582,11 +5582,12 @@ bool Sema::CheckTemplateArgumentList(
     ContextRAII Context(*this, NewContext);
     CXXThisScopeRAII(*this, RD, ThisQuals, RD != nullptr);
 
-    MultiLevelTemplateArgumentList MLTAL = getTemplateInstantiationArgs(
-        Template, NewContext, /*Final=*/false, CanonicalConverted,
-        /*RelativeToPrimary=*/true,
-        /*Pattern=*/nullptr,
-        /*ForConceptInstantiation=*/true);
+    MultiLevelTemplateArgumentList MLTAL =
+        getTemplateInstantiationArgs(Template, Template->getDeclContext(),
+                                     /*Final=*/false, CanonicalConverted,
+                                     /*RelativeToPrimary=*/true,
+                                     /*Pattern=*/nullptr,
+                                     /*ForConceptInstantiation=*/true);
     if (EnsureTemplateArgumentListConstraints(
             Template, MLTAL,
             SourceRange(TemplateLoc, TemplateArgs.getRAngleLoc()))) {

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -492,7 +492,8 @@ MultiLevelTemplateArgumentList Sema::getTemplateInstantiationArgs(
     // has a depth of 0.
     if (const auto *TTP = dyn_cast<TemplateTemplateParmDecl>(CurDecl))
       HandleDefaultTempArgIntoTempTempParam(TTP, Result);
-    CurDecl = Response::UseNextDecl(CurDecl).NextDecl;
+    CurDecl = DC ? Decl::castFromDeclContext(DC)
+                 : Response::UseNextDecl(CurDecl).NextDecl;
   }
 
   while (!CurDecl->isFileContextDecl()) {
@@ -3240,15 +3241,13 @@ bool Sema::SubstDefaultArgument(
           /*ForDefinition*/ false);
       if (addInstantiatedParametersToScope(FD, PatternFD, *LIS, TemplateArgs))
         return true;
-      const FunctionTemplateDecl *PrimaryTemplate = FD->getPrimaryTemplate();
-      if (PrimaryTemplate && PrimaryTemplate->isOutOfLine()) {
-        TemplateArgumentList *CurrentTemplateArgumentList =
-            TemplateArgumentList::CreateCopy(getASTContext(),
-                                             TemplateArgs.getInnermost());
+      // FIXME: Investigate if we shall validate every FunctionTemplateDecl
+      // along the getInstantiatedFromMemberTemplate() chain.
+      if (auto *PrimaryTemplate = FD->getPrimaryTemplate();
+          PrimaryTemplate && PrimaryTemplate->isOutOfLine())
         NewTemplateArgs = getTemplateInstantiationArgs(
             FD, FD->getDeclContext(), /*Final=*/false,
-            CurrentTemplateArgumentList->asArray(), /*RelativeToPrimary=*/true);
-      }
+            TemplateArgs.getInnermost(), /*RelativeToPrimary=*/true);
     }
 
     runWithSufficientStackSpace(Loc, [&] {