[clang][NFC] Remove const-qualification from FunctionTemplateSpecializationInfo::TemplateArguments (#92500)

This patch remove const-qualification from pointee type of
`FunctionTemplateSpecializationInfo::TemplateArguments`, because it's
(eventually) used to initialize `MultiLevelTemplateArgumentList`, which
can actually mutate the arguments via

https://github.com/llvm/llvm-project/blob/f42f57b52dd279e6ae19270d063aeb8d59e3f11c/clang/include/clang/Sema/Template.h#L197-L204
Mutation seems to be required to correctly handle packs:

https://github.com/llvm/llvm-project/blob/9144553207052a868efc5a8ce61a0afbb0eaf236/clang/lib/Sema/SemaTemplateInstantiate.cpp#L1440-L1469

Author: Endilll

clang/include/clang/AST/Decl.h

@@ -2096,13 +2096,12 @@ class FunctionDecl : public DeclaratorDecl,
   ///
   /// \param PointOfInstantiation point at which the function template
   /// specialization was first instantiated.
-  void setFunctionTemplateSpecialization(ASTContext &C,
-                                         FunctionTemplateDecl *Template,
-                                       const TemplateArgumentList *TemplateArgs,
-                                         void *InsertPos,
-                                         TemplateSpecializationKind TSK,
-                          const TemplateArgumentListInfo *TemplateArgsAsWritten,
-                                         SourceLocation PointOfInstantiation);
+  void setFunctionTemplateSpecialization(
+      ASTContext &C, FunctionTemplateDecl *Template,
+      TemplateArgumentList *TemplateArgs, void *InsertPos,
+      TemplateSpecializationKind TSK,
+      const TemplateArgumentListInfo *TemplateArgsAsWritten,
+      SourceLocation PointOfInstantiation);
 
   /// Specify that this record is an instantiation of the
   /// member function FD.
@@ -2981,12 +2980,12 @@ class FunctionDecl : public DeclaratorDecl,
   ///
   /// \param PointOfInstantiation point at which the function template
   /// specialization was first instantiated.
-  void setFunctionTemplateSpecialization(FunctionTemplateDecl *Template,
-                const TemplateArgumentList *TemplateArgs,
-                void *InsertPos,
-                TemplateSpecializationKind TSK = TSK_ImplicitInstantiation,
-                const TemplateArgumentListInfo *TemplateArgsAsWritten = nullptr,
-                SourceLocation PointOfInstantiation = SourceLocation()) {
+  void setFunctionTemplateSpecialization(
+      FunctionTemplateDecl *Template, TemplateArgumentList *TemplateArgs,
+      void *InsertPos,
+      TemplateSpecializationKind TSK = TSK_ImplicitInstantiation,
+      TemplateArgumentListInfo *TemplateArgsAsWritten = nullptr,
+      SourceLocation PointOfInstantiation = SourceLocation()) {
     setFunctionTemplateSpecialization(getASTContext(), Template, TemplateArgs,
                                       InsertPos, TSK, TemplateArgsAsWritten,
                                       PointOfInstantiation);

clang/include/clang/AST/DeclTemplate.h

@@ -478,7 +478,7 @@ class FunctionTemplateSpecializationInfo final
 public:
   /// The template arguments used to produce the function template
   /// specialization from the function template.
-  const TemplateArgumentList *TemplateArguments;
+  TemplateArgumentList *TemplateArguments;
 
   /// The template arguments as written in the sources, if provided.
   /// FIXME: Normally null; tail-allocate this.
@@ -491,7 +491,7 @@ class FunctionTemplateSpecializationInfo final
 private:
   FunctionTemplateSpecializationInfo(
       FunctionDecl *FD, FunctionTemplateDecl *Template,
-      TemplateSpecializationKind TSK, const TemplateArgumentList *TemplateArgs,
+      TemplateSpecializationKind TSK, TemplateArgumentList *TemplateArgs,
       const ASTTemplateArgumentListInfo *TemplateArgsAsWritten,
       SourceLocation POI, MemberSpecializationInfo *MSInfo)
       : Function(FD, MSInfo ? true : false), Template(Template, TSK - 1),
@@ -511,8 +511,7 @@ class FunctionTemplateSpecializationInfo final
 
   static FunctionTemplateSpecializationInfo *
   Create(ASTContext &C, FunctionDecl *FD, FunctionTemplateDecl *Template,
-         TemplateSpecializationKind TSK,
-         const TemplateArgumentList *TemplateArgs,
+         TemplateSpecializationKind TSK, TemplateArgumentList *TemplateArgs,
          const TemplateArgumentListInfo *TemplateArgsAsWritten,
          SourceLocation POI, MemberSpecializationInfo *MSInfo);
 

clang/lib/AST/Decl.cpp

@@ -4199,14 +4199,12 @@ FunctionDecl::getTemplateSpecializationArgsAsWritten() const {
   return nullptr;
 }
 
-void
-FunctionDecl::setFunctionTemplateSpecialization(ASTContext &C,
-                                                FunctionTemplateDecl *Template,
-                                     const TemplateArgumentList *TemplateArgs,
-                                                void *InsertPos,
-                                                TemplateSpecializationKind TSK,
-                        const TemplateArgumentListInfo *TemplateArgsAsWritten,
-                                          SourceLocation PointOfInstantiation) {
+void FunctionDecl::setFunctionTemplateSpecialization(
+    ASTContext &C, FunctionTemplateDecl *Template,
+    TemplateArgumentList *TemplateArgs, void *InsertPos,
+    TemplateSpecializationKind TSK,
+    const TemplateArgumentListInfo *TemplateArgsAsWritten,
+    SourceLocation PointOfInstantiation) {
   assert((TemplateOrSpecialization.isNull() ||
           TemplateOrSpecialization.is<MemberSpecializationInfo *>()) &&
          "Member function is already a specialization");

clang/lib/AST/DeclTemplate.cpp

@@ -884,7 +884,7 @@ TemplateArgumentList::CreateCopy(ASTContext &Context,
 
 FunctionTemplateSpecializationInfo *FunctionTemplateSpecializationInfo::Create(
     ASTContext &C, FunctionDecl *FD, FunctionTemplateDecl *Template,
-    TemplateSpecializationKind TSK, const TemplateArgumentList *TemplateArgs,
+    TemplateSpecializationKind TSK, TemplateArgumentList *TemplateArgs,
     const TemplateArgumentListInfo *TemplateArgsAsWritten, SourceLocation POI,
     MemberSpecializationInfo *MSInfo) {
   const ASTTemplateArgumentListInfo *ArgsAsWritten = nullptr;

clang/lib/Sema/SemaTemplate.cpp

@@ -10500,7 +10500,7 @@ bool Sema::CheckFunctionTemplateSpecialization(
   // specialization, with the template arguments from the previous
   // specialization.
   // Take copies of (semantic and syntactic) template argument lists.
-  const TemplateArgumentList *TemplArgs = TemplateArgumentList::CreateCopy(
+  TemplateArgumentList *TemplArgs = TemplateArgumentList::CreateCopy(
       Context, Specialization->getTemplateSpecializationArgs()->asArray());
   FD->setFunctionTemplateSpecialization(
       Specialization->getPrimaryTemplate(), TemplArgs, /*InsertPos=*/nullptr,