[clang] fix printing of canonical template template parameters take 2 (#93448)

Since they can also occur as the template name of
template specializations, handle them from TemplateName printing instead
of TemplateArgument.

Author: mizvekov

clang/lib/AST/TemplateBase.cpp

@@ -544,16 +544,7 @@ void TemplateArgument::print(const PrintingPolicy &Policy, raw_ostream &Out,
     break;
 
   case Template: {
-    TemplateName TN = getAsTemplate();
-    if (const auto *TD = TN.getAsTemplateDecl();
-        TD && TD->getDeclName().isEmpty()) {
-      assert(isa<TemplateTemplateParmDecl>(TD) &&
-             "Unexpected anonymous template");
-      const auto *TTP = cast<TemplateTemplateParmDecl>(TD);
-      Out << "template-parameter-" << TTP->getDepth() << "-" << TTP->getIndex();
-    } else {
-      TN.print(Out, Policy);
-    }
+    getAsTemplate().print(Out, Policy);
     break;
   }
 

clang/lib/AST/TemplateName.cpp

@@ -292,6 +292,14 @@ void TemplateName::Profile(llvm::FoldingSetNodeID &ID) {
 
 void TemplateName::print(raw_ostream &OS, const PrintingPolicy &Policy,
                          Qualified Qual) const {
+  auto handleAnonymousTTP = [](TemplateDecl *TD, raw_ostream &OS) {
+    if (TemplateTemplateParmDecl *TTP = dyn_cast<TemplateTemplateParmDecl>(TD);
+        TTP && TTP->getIdentifier() == nullptr) {
+      OS << "template-parameter-" << TTP->getDepth() << "-" << TTP->getIndex();
+      return true;
+    }
+    return false;
+  };
   if (NameKind Kind = getKind();
       Kind == TemplateName::Template || Kind == TemplateName::UsingTemplate) {
     // After `namespace ns { using std::vector }`, what is the fully-qualified
@@ -304,6 +312,8 @@ void TemplateName::print(raw_ostream &OS, const PrintingPolicy &Policy,
     // names more often than to export them, thus using the original name is
     // most useful in this case.
     TemplateDecl *Template = getAsTemplateDecl();
+    if (handleAnonymousTTP(Template, OS))
+      return;
     if (Qual == Qualified::None)
       OS << *Template;
     else
@@ -320,6 +330,10 @@ void TemplateName::print(raw_ostream &OS, const PrintingPolicy &Policy,
            Underlying.getKind() == TemplateName::UsingTemplate);
 
     TemplateDecl *UTD = Underlying.getAsTemplateDecl();
+
+    if (handleAnonymousTTP(UTD, OS))
+      return;
+
     if (IdentifierInfo *II = UTD->getIdentifier();
         Policy.CleanUglifiedParameters && II &&
         isa<TemplateTemplateParmDecl>(UTD))

clang/test/SemaTemplate/deduction-guide.cpp

@@ -315,19 +315,19 @@ namespace TTP {
 // CHECK-NEXT:  |-TemplateTypeParmDecl {{.+}} class depth 0 index 0 T{{$}}
 // CHECK-NEXT:  |-TemplateTemplateParmDecl {{.+}} depth 0 index 1 TT{{$}}
 // CHECK-NEXT:  | `-TemplateTypeParmDecl {{.+}} class depth 1 index 0{{$}}
-// CHECK-NEXT:  |-CXXDeductionGuideDecl {{.+}} 'auto (<T>) -> B<T>'{{$}}
-// CHECK-NEXT:  | `-ParmVarDecl {{.+}} '<T>'{{$}}
+// CHECK-NEXT:  |-CXXDeductionGuideDecl {{.+}} 'auto (template-parameter-0-1<T>) -> B<T>'{{$}}
+// CHECK-NEXT:  | `-ParmVarDecl {{.+}} 'template-parameter-0-1<T>'{{$}}
 // CHECK-NEXT:  `-CXXDeductionGuideDecl {{.+}} 'auto (A<int>) -> TTP::B<int>'
 // CHECK-NEXT:    |-TemplateArgument type 'int'
 // CHECK-NEXT:    | `-BuiltinType {{.+}} 'int'{{$}}
 // CHECK-NEXT:    |-TemplateArgument template 'TTP::A'{{$}}
 // CHECK-NEXT:    | `-ClassTemplateDecl {{.+}} A{{$}}
 // CHECK-NEXT:    `-ParmVarDecl {{.+}} 'A<int>':'TTP::A<int>'{{$}}
-// CHECK-NEXT:  FunctionProtoType {{.+}} 'auto (<T>) -> B<T>' dependent trailing_return cdecl{{$}}
+// CHECK-NEXT:  FunctionProtoType {{.+}} 'auto (template-parameter-0-1<T>) -> B<T>' dependent trailing_return cdecl{{$}}
 // CHECK-NEXT:  |-InjectedClassNameType {{.+}} 'B<T>' dependent{{$}}
 // CHECK-NEXT:  | `-CXXRecord {{.+}} 'B'{{$}}
-// CHECK-NEXT:  `-ElaboratedType {{.+}} '<T>' sugar dependent{{$}}
-// CHECK-NEXT:    `-TemplateSpecializationType {{.+}} '<T>' dependent {{$}}
+// CHECK-NEXT:  `-ElaboratedType {{.+}} 'template-parameter-0-1<T>' sugar dependent{{$}}
+// CHECK-NEXT:    `-TemplateSpecializationType {{.+}} 'template-parameter-0-1<T>' dependent template-parameter-0-1{{$}}
 // CHECK-NEXT:      `-TemplateArgument type 'T':'type-parameter-0-0'{{$}}
 // CHECK-NEXT:        `-TemplateTypeParmType {{.+}} 'T' dependent depth 0 index 0{{$}}
 // CHECK-NEXT:          `-TemplateTypeParm {{.+}} 'T'{{$}}