diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 6dfb2d7195203..e0ac3af7b98e3 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -4933,6 +4933,8 @@ def err_template_param_shadow : Error<
 def ext_template_param_shadow : ExtWarn<
   err_template_param_shadow.Summary>, InGroup<MicrosoftTemplateShadow>;
 def note_template_param_here : Note<"template parameter is declared here">;
+def note_template_param_external : Note<
+  "template parameter from hidden source: %0">;
 def warn_template_export_unsupported : Warning<
   "exported templates are unsupported">;
 def err_template_outside_namespace_or_class_scope : Error<
@@ -5061,6 +5063,8 @@ def err_template_arg_list_different_arity : Error<
   "%select{class template|function template|variable template|alias template|"
   "template template parameter|concept|template}1 %2">;
 def note_template_decl_here : Note<"template is declared here">;
+def note_template_decl_external : Note<
+  "template declaration from hidden source: %0">;
 def err_template_arg_must_be_type : Error<
   "template argument for template type parameter must be a type">;
 def err_template_arg_must_be_type_suggest : Error<
diff --git a/clang/include/clang/Sema/HLSLExternalSemaSource.h b/clang/include/clang/Sema/HLSLExternalSemaSource.h
index 4b6bc96f72e22..c0bfff327139f 100644
--- a/clang/include/clang/Sema/HLSLExternalSemaSource.h
+++ b/clang/include/clang/Sema/HLSLExternalSemaSource.h
@@ -30,9 +30,9 @@ class HLSLExternalSemaSource : public ExternalSemaSource {
 
   void defineHLSLVectorAlias();
   void defineTrivialHLSLTypes();
-  void forwardDeclareHLSLTypes();
+  void defineHLSLTypesWithForwardDeclarations();
 
-  void completeBufferType(CXXRecordDecl *Record);
+  void onCompletion(CXXRecordDecl *Record, CompletionFunction Fn);
 
 public:
   ~HLSLExternalSemaSource() override;
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 6de1a098e067a..a4912e3625c38 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -8557,6 +8557,10 @@ class Sema final {
                                      TemplateParameterList *Params,
                                      TemplateArgumentLoc &Arg);
 
+  void NoteTemplateLocation(const NamedDecl &Decl,
+                            std::optional<SourceRange> ParamRange = {});
+  void NoteTemplateParameterLocation(const NamedDecl &Decl);
+
   ExprResult
   BuildExpressionFromDeclTemplateArgument(const TemplateArgument &Arg,
                                           QualType ParamType,
diff --git a/clang/lib/Sema/HLSLExternalSemaSource.cpp b/clang/lib/Sema/HLSLExternalSemaSource.cpp
index 8de144486c91d..8ed6480a9f5c9 100644
--- a/clang/lib/Sema/HLSLExternalSemaSource.cpp
+++ b/clang/lib/Sema/HLSLExternalSemaSource.cpp
@@ -306,6 +306,7 @@ struct BuiltinTypeDeclBuilder {
   }
 
   TemplateParameterListBuilder addTemplateArgumentList();
+  BuiltinTypeDeclBuilder &addSimpleTemplateParams(ArrayRef<StringRef> Names);
 };
 
 struct TemplateParameterListBuilder {
@@ -360,11 +361,19 @@ struct TemplateParameterListBuilder {
     return Builder;
   }
 };
+} // namespace
 
 TemplateParameterListBuilder BuiltinTypeDeclBuilder::addTemplateArgumentList() {
   return TemplateParameterListBuilder(*this);
 }
-} // namespace
+
+BuiltinTypeDeclBuilder &
+BuiltinTypeDeclBuilder::addSimpleTemplateParams(ArrayRef<StringRef> Names) {
+  TemplateParameterListBuilder Builder = this->addTemplateArgumentList();
+  for (StringRef Name : Names)
+    Builder.addTypeParameter(Name);
+  return Builder.finalizeTemplateArgs();
+}
 
 HLSLExternalSemaSource::~HLSLExternalSemaSource() {}
 
@@ -390,7 +399,7 @@ void HLSLExternalSemaSource::InitializeSema(Sema &S) {
   // Force external decls in the HLSL namespace to load from the PCH.
   (void)HLSLNamespace->getCanonicalDecl()->decls_begin();
   defineTrivialHLSLTypes();
-  forwardDeclareHLSLTypes();
+  defineHLSLTypesWithForwardDeclarations();
 
   // This adds a `using namespace hlsl` directive. In DXC, we don't put HLSL's
   // built in types inside a namespace, but we are planning to change that in
@@ -467,18 +476,32 @@ void HLSLExternalSemaSource::defineTrivialHLSLTypes() {
                      .Record;
 }
 
-void HLSLExternalSemaSource::forwardDeclareHLSLTypes() {
+/// Set up common members and attributes for buffer types
+static BuiltinTypeDeclBuilder setupBufferType(CXXRecordDecl *Decl, Sema &S,
+                                              ResourceClass RC,
+                                              ResourceKind RK) {
+  return BuiltinTypeDeclBuilder(Decl)
+      .addHandleMember()
+      .addDefaultHandleConstructor(S, RC)
+      .annotateResourceClass(RC, RK);
+}
+
+void HLSLExternalSemaSource::defineHLSLTypesWithForwardDeclarations() {
   CXXRecordDecl *Decl;
   Decl = BuiltinTypeDeclBuilder(*SemaPtr, HLSLNamespace, "RWBuffer")
-             .addTemplateArgumentList()
-             .addTypeParameter("element_type", SemaPtr->getASTContext().FloatTy)
-             .finalizeTemplateArgs()
+             .addSimpleTemplateParams({"element_type"})
              .Record;
-  if (!Decl->isCompleteDefinition())
-    Completions.insert(
-        std::make_pair(Decl->getCanonicalDecl(),
-                       std::bind(&HLSLExternalSemaSource::completeBufferType,
-                                 this, std::placeholders::_1)));
+  onCompletion(Decl, [this](CXXRecordDecl *Decl) {
+    setupBufferType(Decl, *SemaPtr, ResourceClass::UAV,
+                    ResourceKind::TypedBuffer)
+        .addArraySubscriptOperators()
+        .completeDefinition();
+  });
+}
+
+void HLSLExternalSemaSource::onCompletion(CXXRecordDecl *Record,
+                                          CompletionFunction Fn) {
+  Completions.insert(std::make_pair(Record->getCanonicalDecl(), Fn));
 }
 
 void HLSLExternalSemaSource::CompleteType(TagDecl *Tag) {
@@ -496,12 +519,3 @@ void HLSLExternalSemaSource::CompleteType(TagDecl *Tag) {
     return;
   It->second(Record);
 }
-
-void HLSLExternalSemaSource::completeBufferType(CXXRecordDecl *Record) {
-  BuiltinTypeDeclBuilder(Record)
-      .addHandleMember()
-      .addDefaultHandleConstructor(*SemaPtr, ResourceClass::UAV)
-      .addArraySubscriptOperators()
-      .annotateResourceClass(ResourceClass::UAV, ResourceKind::TypedBuffer)
-      .completeDefinition();
-}
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index c0d21ec330acf..e6d4655644c62 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -5971,7 +5971,7 @@ Sema::GetNameFromUnqualifiedId(const UnqualifiedId &Name) {
            diag::err_deduction_guide_name_not_class_template)
         << (int)getTemplateNameKindForDiagnostics(TN) << TN;
       if (Template)
-        Diag(Template->getLocation(), diag::note_template_decl_here);
+        NoteTemplateLocation(*Template);
       return DeclarationNameInfo();
     }
 
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 7385eac48d8c8..bece54b4bfa14 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -11462,7 +11462,7 @@ bool Sema::CheckDeductionGuideDeclarator(Declarator &D, QualType &R,
           GuidedTemplateDecl->getDeclContext()->getRedeclContext())) {
     Diag(D.getIdentifierLoc(), diag::err_deduction_guide_wrong_scope)
       << GuidedTemplateDecl;
-    Diag(GuidedTemplateDecl->getLocation(), diag::note_template_decl_here);
+    NoteTemplateLocation(*GuidedTemplateDecl);
   }
 
   auto &DS = D.getMutableDeclSpec();
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index 50ee0a5acb558..042ca61abe44d 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -10573,7 +10573,7 @@ QualType Sema::DeduceTemplateSpecializationFromInitializer(
          diag::err_deduced_non_class_template_specialization_type)
       << (int)getTemplateNameKindForDiagnostics(TemplateName) << TemplateName;
     if (auto *TD = TemplateName.getAsTemplateDecl())
-      Diag(TD->getLocation(), diag::note_template_decl_here);
+      NoteTemplateLocation(*TD);
     return QualType();
   }
 
diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
index ca09b0481bcac..4cc87c9fa765c 100644
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -1444,7 +1444,7 @@ void Sema::ActOnStartOfLambdaDefinition(LambdaIntroducer &Intro,
       for (const auto &Capture : Intro.Captures) {
         if (Capture.Id == TP->getIdentifier()) {
           Diag(Capture.Loc, diag::err_template_param_shadow) << Capture.Id;
-          Diag(TP->getLocation(), diag::note_template_param_here);
+          NoteTemplateParameterLocation(*TP);
         }
       }
     }
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 34d7b8c731e90..be9e294a72f31 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -820,7 +820,6 @@ bool Sema::DiagnoseUninstantiableTemplate(SourceLocation PointOfInstantiation,
   if (!Complain || (PatternDef && PatternDef->isInvalidDecl()))
     return true;
 
-  std::optional<unsigned> Note;
   QualType InstantiationTy;
   if (TagDecl *TD = dyn_cast<TagDecl>(Instantiation))
     InstantiationTy = Context.getTypeDeclType(TD);
@@ -838,25 +837,25 @@ bool Sema::DiagnoseUninstantiableTemplate(SourceLocation PointOfInstantiation,
            diag::err_explicit_instantiation_undefined_member)
         << /*member function*/ 1 << Instantiation->getDeclName()
         << Instantiation->getDeclContext();
-      Note = diag::note_explicit_instantiation_here;
+      Diag(Pattern->getLocation(), diag::note_explicit_instantiation_here);
     } else {
       assert(isa<TagDecl>(Instantiation) && "Must be a TagDecl!");
       Diag(PointOfInstantiation,
            diag::err_implicit_instantiate_member_undefined)
         << InstantiationTy;
-      Note = diag::note_member_declared_at;
+      Diag(Pattern->getLocation(), diag::note_member_declared_at);
     }
   } else {
     if (isa<FunctionDecl>(Instantiation)) {
       Diag(PointOfInstantiation,
            diag::err_explicit_instantiation_undefined_func_template)
         << Pattern;
-      Note = diag::note_explicit_instantiation_here;
+      Diag(Pattern->getLocation(), diag::note_explicit_instantiation_here);
     } else if (isa<TagDecl>(Instantiation)) {
       Diag(PointOfInstantiation, diag::err_template_instantiate_undefined)
         << (TSK != TSK_ImplicitInstantiation)
         << InstantiationTy;
-      Note = diag::note_template_decl_here;
+      NoteTemplateLocation(*Pattern);
     } else {
       assert(isa<VarDecl>(Instantiation) && "Must be a VarDecl!");
       if (isa<VarTemplateSpecializationDecl>(Instantiation)) {
@@ -869,11 +868,9 @@ bool Sema::DiagnoseUninstantiableTemplate(SourceLocation PointOfInstantiation,
              diag::err_explicit_instantiation_undefined_member)
           << /*static data member*/ 2 << Instantiation->getDeclName()
           << Instantiation->getDeclContext();
-      Note = diag::note_explicit_instantiation_here;
+      Diag(Pattern->getLocation(), diag::note_explicit_instantiation_here);
     }
   }
-  if (Note) // Diagnostics were emitted.
-    Diag(Pattern->getLocation(), *Note);
 
   // In general, Instantiation isn't marked invalid to get more than one
   // error for multiple undefined instantiations. But the code that does
@@ -898,8 +895,9 @@ void Sema::DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl) {
   // Make this a warning when MSVC compatibility is requested.
   unsigned DiagId = getLangOpts().MSVCCompat ? diag::ext_template_param_shadow
                                              : diag::err_template_param_shadow;
-  Diag(Loc, DiagId) << cast<NamedDecl>(PrevDecl)->getDeclName();
-  Diag(PrevDecl->getLocation(), diag::note_template_param_here);
+  NamedDecl *ND = cast<NamedDecl>(PrevDecl);
+  Diag(Loc, DiagId) << ND->getDeclName();
+  NoteTemplateParameterLocation(*ND);
 }
 
 /// AdjustDeclIfTemplate - If the given decl happens to be a template, reset
@@ -4488,7 +4486,7 @@ static void checkMoreSpecializedThanPrimary(Sema &S, PartialSpecDecl *Partial) {
       << SFINAEArgString;
   }
 
-  S.Diag(Template->getLocation(), diag::note_template_decl_here);
+  S.NoteTemplateLocation(*Template);
   SmallVector<const Expr *, 3> PartialAC, TemplateAC;
   Template->getAssociatedConstraints(TemplateAC);
   Partial->getAssociatedConstraints(PartialAC);
@@ -4966,8 +4964,7 @@ void Sema::diagnoseMissingTemplateArguments(TemplateName Name,
   Diag(Loc, diag::err_template_missing_args)
     << (int)getTemplateNameKindForDiagnostics(Name) << Name;
   if (TemplateDecl *TD = Name.getAsTemplateDecl()) {
-    Diag(TD->getLocation(), diag::note_template_decl_here)
-      << TD->getTemplateParameters()->getSourceRange();
+    NoteTemplateLocation(*TD, TD->getTemplateParameters()->getSourceRange());
   }
 }
 
@@ -5319,7 +5316,7 @@ bool Sema::CheckTemplateTypeArgument(
                       ? diag::ext_ms_template_type_arg_missing_typename
                       : diag::err_template_arg_must_be_type_suggest)
             << FixItHint::CreateInsertion(Loc, "typename ");
-        Diag(Param->getLocation(), diag::note_template_param_here);
+        NoteTemplateParameterLocation(*Param);
 
         // Recover by synthesizing a type using the location information that we
         // already have.
@@ -5348,7 +5345,7 @@ bool Sema::CheckTemplateTypeArgument(
     // is not a type.
     SourceRange SR = AL.getSourceRange();
     Diag(SR.getBegin(), diag::err_template_arg_must_be_type) << SR;
-    Diag(Param->getLocation(), diag::note_template_param_here);
+    NoteTemplateParameterLocation(*Param);
 
     return true;
   }
@@ -5794,8 +5791,8 @@ bool Sema::CheckTemplateArgument(
       // therefore cannot be a non-type template argument.
       Diag(Arg.getLocation(), diag::err_template_arg_must_be_expr)
         << Arg.getSourceRange();
+      NoteTemplateParameterLocation(*Param);
 
-      Diag(Param->getLocation(), diag::note_template_param_here);
       return true;
 
     case TemplateArgument::Type: {
@@ -5815,7 +5812,7 @@ bool Sema::CheckTemplateArgument(
         Diag(SR.getBegin(), diag::err_template_arg_nontype_ambig) << SR << T;
       else
         Diag(SR.getBegin(), diag::err_template_arg_must_be_expr) << SR;
-      Diag(Param->getLocation(), diag::note_template_param_here);
+      NoteTemplateParameterLocation(*Param);
       return true;
     }
 
@@ -5936,8 +5933,7 @@ static bool diagnoseMissingArgument(Sema &S, SourceLocation Loc,
     << /*not enough args*/0
     << (int)S.getTemplateNameKindForDiagnostics(TemplateName(TD))
     << TD;
-  S.Diag(TD->getLocation(), diag::note_template_decl_here)
-    << Params->getSourceRange();
+  S.NoteTemplateLocation(*TD, Params->getSourceRange());
   return true;
 }
 
@@ -6003,8 +5999,7 @@ bool Sema::CheckTemplateArgumentList(
           << /*not enough args*/0
           << (int)getTemplateNameKindForDiagnostics(TemplateName(Template))
           << Template;
-        Diag(Template->getLocation(), diag::note_template_decl_here)
-          << Params->getSourceRange();
+        NoteTemplateLocation(*Template, Params->getSourceRange());
         return true;
       }
     }
@@ -6036,7 +6031,7 @@ bool Sema::CheckTemplateArgumentList(
              diag::err_template_expansion_into_fixed_list)
           << (isa<ConceptDecl>(Template) ? 1 : 0)
           << NewArgs[ArgIdx].getSourceRange();
-        Diag((*Param)->getLocation(), diag::note_template_param_here);
+        NoteTemplateParameterLocation(**Param);
         return true;
       }
 
@@ -6232,8 +6227,7 @@ bool Sema::CheckTemplateArgumentList(
         << (int)getTemplateNameKindForDiagnostics(TemplateName(Template))
         << Template
         << SourceRange(NewArgs[ArgIdx].getLocation(), NewArgs.getRAngleLoc());
-    Diag(Template->getLocation(), diag::note_template_decl_here)
-        << Params->getSourceRange();
+    NoteTemplateLocation(*Template, Params->getSourceRange());
     return true;
   }
 
@@ -6645,7 +6639,7 @@ isNullPointerValueTemplateArgument(Sema &S, NonTypeTemplateParmDecl *Param,
     for (unsigned I = 0, N = Notes.size(); I != N; ++I)
       S.Diag(Notes[I].first, Notes[I].second);
 
-    S.Diag(Param->getLocation(), diag::note_template_param_here);
+    S.NoteTemplateParameterLocation(*Param);
     return NPV_Error;
   }
 
@@ -6671,7 +6665,7 @@ isNullPointerValueTemplateArgument(Sema &S, NonTypeTemplateParmDecl *Param,
     // then recover as if the types were correct.
     S.Diag(Arg->getExprLoc(), diag::err_template_arg_wrongtype_null_constant)
       << Arg->getType() << ParamType << Arg->getSourceRange();
-    S.Diag(Param->getLocation(), diag::note_template_param_here);
+    S.NoteTemplateParameterLocation(*Param);
     return NPV_NullPointer;
   }
 
@@ -6681,7 +6675,7 @@ isNullPointerValueTemplateArgument(Sema &S, NonTypeTemplateParmDecl *Param,
     // message with the information we have here.
     S.Diag(Arg->getExprLoc(), diag::err_template_arg_invalid)
       << EvalResult.Val.getAsString(S.Context, ParamType);
-    S.Diag(Param->getLocation(), diag::note_template_param_here);
+    S.NoteTemplateParameterLocation(*Param);
     return NPV_Error;
   }
 
@@ -6693,7 +6687,7 @@ isNullPointerValueTemplateArgument(Sema &S, NonTypeTemplateParmDecl *Param,
         << ParamType << FixItHint::CreateInsertion(Arg->getBeginLoc(), Code)
         << FixItHint::CreateInsertion(S.getLocForEndOfToken(Arg->getEndLoc()),
                                       ")");
-    S.Diag(Param->getLocation(), diag::note_template_param_here);
+    S.NoteTemplateParameterLocation(*Param);
     return NPV_NullPointer;
   }
 
@@ -6734,7 +6728,7 @@ static bool CheckTemplateArgumentIsCompatibleWithParameter(
           S.Diag(Arg->getBeginLoc(),
                  diag::err_template_arg_ref_bind_ignores_quals)
               << ParamType << Arg->getType() << Arg->getSourceRange();
-          S.Diag(Param->getLocation(), diag::note_template_param_here);
+          S.NoteTemplateParameterLocation(*Param);
           return true;
         }
       }
@@ -6752,7 +6746,7 @@ static bool CheckTemplateArgumentIsCompatibleWithParameter(
       else
         S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_convertible)
             << ArgIn->getType() << ParamType << Arg->getSourceRange();
-      S.Diag(Param->getLocation(), diag::note_template_param_here);
+      S.NoteTemplateParameterLocation(*Param);
       return true;
     }
   }
@@ -6895,7 +6889,7 @@ static bool CheckTemplateArgumentAddressOfObjectOrFunction(
   if (!Entity) {
     S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_decl_ref)
         << Arg->getSourceRange();
-    S.Diag(Param->getLocation(), diag::note_template_param_here);
+    S.NoteTemplateParameterLocation(*Param);
     return true;
   }
 
@@ -6903,7 +6897,7 @@ static bool CheckTemplateArgumentAddressOfObjectOrFunction(
   if (isa<FieldDecl>(Entity) || isa<IndirectFieldDecl>(Entity)) {
     S.Diag(Arg->getBeginLoc(), diag::err_template_arg_field)
         << Entity << Arg->getSourceRange();
-    S.Diag(Param->getLocation(), diag::note_template_param_here);
+    S.NoteTemplateParameterLocation(*Param);
     return true;
   }
 
@@ -6912,7 +6906,7 @@ static bool CheckTemplateArgumentAddressOfObjectOrFunction(
     if (!Method->isStatic()) {
       S.Diag(Arg->getBeginLoc(), diag::err_template_arg_method)
           << Method << Arg->getSourceRange();
-      S.Diag(Param->getLocation(), diag::note_template_param_here);
+      S.NoteTemplateParameterLocation(*Param);
       return true;
     }
   }
@@ -6952,7 +6946,7 @@ static bool CheckTemplateArgumentAddressOfObjectOrFunction(
     if (Var->getType()->isReferenceType()) {
       S.Diag(Arg->getBeginLoc(), diag::err_template_arg_reference_var)
           << Var->getType() << Arg->getSourceRange();
-      S.Diag(Param->getLocation(), diag::note_template_param_here);
+      S.NoteTemplateParameterLocation(*Param);
       return true;
     }
 
@@ -6973,14 +6967,14 @@ static bool CheckTemplateArgumentAddressOfObjectOrFunction(
                                           ParamType.getNonReferenceType())) {
       S.Diag(AddrOpLoc, diag::err_template_arg_address_of_non_pointer)
         << ParamType;
-      S.Diag(Param->getLocation(), diag::note_template_param_here);
+      S.NoteTemplateParameterLocation(*Param);
       return true;
     }
 
     S.Diag(AddrOpLoc, diag::err_template_arg_address_of_non_pointer)
       << ParamType
       << FixItHint::CreateRemoval(AddrOpLoc);
-    S.Diag(Param->getLocation(), diag::note_template_param_here);
+    S.NoteTemplateParameterLocation(*Param);
 
     ArgType = Entity->getType();
   }
@@ -7002,14 +6996,14 @@ static bool CheckTemplateArgumentAddressOfObjectOrFunction(
       if (!S.Context.hasSameUnqualifiedType(ArgType, ParamType)) {
         S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_address_of)
           << ParamType;
-        S.Diag(Param->getLocation(), diag::note_template_param_here);
+        S.NoteTemplateParameterLocation(*Param);
         return true;
       }
 
       S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_address_of)
         << ParamType << FixItHint::CreateInsertion(Arg->getBeginLoc(), "&");
 
-      S.Diag(Param->getLocation(), diag::note_template_param_here);
+      S.NoteTemplateParameterLocation(*Param);
     }
   }
 
@@ -7125,7 +7119,7 @@ CheckTemplateArgumentPointerToMember(Sema &S, NonTypeTemplateParmDecl *Param,
     // We can't perform this conversion.
     S.Diag(ResultArg->getBeginLoc(), diag::err_template_arg_not_convertible)
         << ResultArg->getType() << ParamType << ResultArg->getSourceRange();
-    S.Diag(Param->getLocation(), diag::note_template_param_here);
+    S.NoteTemplateParameterLocation(*Param);
     return true;
   }
 
@@ -7237,7 +7231,7 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
              diag::err_non_type_template_parm_type_deduction_failure)
             << Param->getDeclName() << Param->getType() << Arg->getType()
             << Arg->getSourceRange();
-        Diag(Param->getLocation(), diag::note_template_param_here);
+        NoteTemplateParameterLocation(*Param);
         return ExprError();
       }
     }
@@ -7247,7 +7241,7 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
     // where the parameter type is deduced.
     ParamType = CheckNonTypeTemplateParameterType(ParamType, Arg->getExprLoc());
     if (ParamType.isNull()) {
-      Diag(Param->getLocation(), diag::note_template_param_here);
+      NoteTemplateParameterLocation(*Param);
       return ExprError();
     }
   }
@@ -7283,7 +7277,7 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
     Diag(StartLoc, diag::err_deduced_non_type_template_arg_type_mismatch)
       << Arg->getType()
       << ParamType.getUnqualifiedType();
-    Diag(Param->getLocation(), diag::note_template_param_here);
+    NoteTemplateParameterLocation(*Param);
     return ExprError();
   }
 
@@ -7548,7 +7542,7 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
     if (!ArgType->isIntegralOrEnumerationType()) {
       Diag(Arg->getBeginLoc(), diag::err_template_arg_not_integral_or_enumeral)
           << ArgType << Arg->getSourceRange();
-      Diag(Param->getLocation(), diag::note_template_param_here);
+      NoteTemplateParameterLocation(*Param);
       return ExprError();
     } else if (!Arg->isValueDependent()) {
       class TmplArgICEDiagnoser : public VerifyICEDiagnoser {
@@ -7586,7 +7580,7 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
       // We can't perform this conversion.
       Diag(Arg->getBeginLoc(), diag::err_template_arg_not_convertible)
           << Arg->getType() << ParamType << Arg->getSourceRange();
-      Diag(Param->getLocation(), diag::note_template_param_here);
+      NoteTemplateParameterLocation(*Param);
       return ExprError();
     }
 
@@ -7632,7 +7626,7 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
         Diag(Arg->getBeginLoc(), diag::warn_template_arg_negative)
             << toString(OldValue, 10) << toString(Value, 10) << Param->getType()
             << Arg->getSourceRange();
-        Diag(Param->getLocation(), diag::note_template_param_here);
+        NoteTemplateParameterLocation(*Param);
       }
 
       // Complain if we overflowed the template parameter's type.
@@ -7647,7 +7641,7 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
         Diag(Arg->getBeginLoc(), diag::warn_template_arg_too_large)
             << toString(OldValue, 10) << toString(Value, 10) << Param->getType()
             << Arg->getSourceRange();
-        Diag(Param->getLocation(), diag::note_template_param_here);
+        NoteTemplateParameterLocation(*Param);
       }
     }
 
@@ -7774,7 +7768,7 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
     case NPV_NotNullPointer:
       Diag(Arg->getExprLoc(), diag::err_template_arg_not_convertible)
         << Arg->getType() << ParamType;
-      Diag(Param->getLocation(), diag::note_template_param_here);
+      NoteTemplateParameterLocation(*Param);
       return ExprError();
 
     case NPV_Error:
@@ -7909,6 +7903,37 @@ bool Sema::CheckTemplateTemplateArgument(TemplateTemplateParmDecl *Param,
                                          Arg.getLocation());
 }
 
+static Sema::SemaDiagnosticBuilder noteLocation(Sema &S, const NamedDecl &Decl,
+                                                unsigned HereDiagID,
+                                                unsigned ExternalDiagID) {
+  if (Decl.getLocation().isValid())
+    return S.Diag(Decl.getLocation(), HereDiagID);
+
+  SmallString<128> Str;
+  llvm::raw_svector_ostream Out(Str);
+  PrintingPolicy PP = S.getPrintingPolicy();
+  PP.TerseOutput = 1;
+  Decl.print(Out, PP);
+  return S.Diag(Decl.getLocation(), ExternalDiagID) << Out.str();
+}
+
+void Sema::NoteTemplateLocation(const NamedDecl &Decl,
+                                std::optional<SourceRange> ParamRange) {
+  SemaDiagnosticBuilder DB =
+      noteLocation(*this, Decl, diag::note_template_decl_here,
+                   diag::note_template_decl_external);
+  if (ParamRange && ParamRange->isValid()) {
+    assert(Decl.getLocation().isValid() &&
+           "Parameter range has location when Decl does not");
+    DB << *ParamRange;
+  }
+}
+
+void Sema::NoteTemplateParameterLocation(const NamedDecl &Decl) {
+  noteLocation(*this, Decl, diag::note_template_param_here,
+               diag::note_template_param_external);
+}
+
 /// Given a non-type template argument that refers to a
 /// declaration and the type of its corresponding non-type template
 /// parameter, produce an expression that properly refers to that
@@ -8634,9 +8659,7 @@ static bool CheckNonTypeTemplatePartialSpecializationArgs(
       S.Diag(IsDefaultArgument ? TemplateNameLoc : ArgExpr->getBeginLoc(),
              diag::err_dependent_typed_non_type_arg_in_partial_spec)
           << Param->getType();
-      S.Diag(Param->getLocation(), diag::note_template_param_here)
-        << (IsDefaultArgument ? ParamUseRange : SourceRange())
-        << ParamUseRange;
+      S.NoteTemplateParameterLocation(*Param);
       return true;
     }
   }
@@ -11216,7 +11239,7 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
           else
             Diag(IILoc, diag::err_deduced_tst)
               << (int)getTemplateNameKindForDiagnostics(TemplateName(TD));
-          Diag(TD->getLocation(), diag::note_template_decl_here);
+          NoteTemplateLocation(*TD);
           return QualType();
         }
         return Context.getElaboratedType(
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 56d133f20a293..83610503ed9b1 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -3792,7 +3792,7 @@ static QualType GetDeclSpecTypeForDeclarator(TypeProcessingState &state,
         << Kind << Error << (int)SemaRef.getTemplateNameKindForDiagnostics(TN)
         << QualType(Deduced, 0) << AutoRange;
       if (auto *TD = TN.getAsTemplateDecl())
-        SemaRef.Diag(TD->getLocation(), diag::note_template_decl_here);
+        SemaRef.NoteTemplateLocation(*TD);
 
       T = SemaRef.Context.IntTy;
       D.setInvalidType(true);
diff --git a/clang/test/AST/HLSL/RWBuffer-AST.hlsl b/clang/test/AST/HLSL/RWBuffer-AST.hlsl
index 9dd9244b73eed..c1613520a146c 100644
--- a/clang/test/AST/HLSL/RWBuffer-AST.hlsl
+++ b/clang/test/AST/HLSL/RWBuffer-AST.hlsl
@@ -13,8 +13,6 @@
 
 // EMPTY: ClassTemplateDecl 0x{{[0-9A-Fa-f]+}} <<invalid sloc>> <invalid sloc> implicit RWBuffer
 // EMPTY-NEXT: TemplateTypeParmDecl 0x{{[0-9A-Fa-f]+}} <<invalid sloc>> <invalid sloc> class depth 0 index 0 element_type
-// EMPTY-NEXT: TemplateArgument type 'float'
-// EMPTY-NEXT: BuiltinType 0x{{[0-9A-Fa-f]+}} 'float'
 // EMPTY-NEXT: CXXRecordDecl 0x{{[0-9A-Fa-f]+}} <<invalid sloc>> <invalid sloc> implicit <undeserialized declarations> class RWBuffer
 // EMPTY-NEXT: FinalAttr 0x{{[0-9A-Fa-f]+}} <<invalid sloc>> Implicit final
 
@@ -33,8 +31,6 @@ RWBuffer<float> Buffer;
 
 // CHECK: ClassTemplateDecl 0x{{[0-9A-Fa-f]+}} <<invalid sloc>> <invalid sloc> implicit RWBuffer
 // CHECK-NEXT: TemplateTypeParmDecl 0x{{[0-9A-Fa-f]+}} <<invalid sloc>> <invalid sloc> class depth 0 index 0 element_type
-// CHECK-NEXT: TemplateArgument type 'float'
-// CHECK-NEXT: BuiltinType 0x{{[0-9A-Fa-f]+}} 'float'
 // CHECK-NEXT: CXXRecordDecl 0x{{[0-9A-Fa-f]+}} <<invalid sloc>> <invalid sloc> implicit class RWBuffer definition
 
 // CHECK: FinalAttr 0x{{[0-9A-Fa-f]+}} <<invalid sloc>> Implicit final
diff --git a/clang/test/AST/HLSL/pch.hlsl b/clang/test/AST/HLSL/pch.hlsl
index 74254fedf27cb..27fae8f499daa 100644
--- a/clang/test/AST/HLSL/pch.hlsl
+++ b/clang/test/AST/HLSL/pch.hlsl
@@ -6,7 +6,7 @@
 
 // Make sure PCH works by using function declared in PCH header and declare a RWBuffer in current file.
 // CHECK:FunctionDecl 0x[[FOO:[0-9a-f]+]] <{{.*}}:2:1, line:4:1> line:2:8 imported used foo 'float2 (float2, float2)'
-// CHECK:VarDecl 0x{{[0-9a-f]+}} <{{.*}}:10:1, col:23> col:23 Buffer 'hlsl::RWBuffer<float>':'hlsl::RWBuffer<>'
+// CHECK:VarDecl 0x{{[0-9a-f]+}} <{{.*}}:10:1, col:23> col:23 Buffer 'hlsl::RWBuffer<float>'
 hlsl::RWBuffer<float> Buffer;
 
 float2 bar(float2 a, float2 b) {
diff --git a/clang/test/AST/HLSL/pch_with_buf.hlsl b/clang/test/AST/HLSL/pch_with_buf.hlsl
index 4e657606cbcb1..e8eae533af629 100644
--- a/clang/test/AST/HLSL/pch_with_buf.hlsl
+++ b/clang/test/AST/HLSL/pch_with_buf.hlsl
@@ -5,9 +5,9 @@
 // Make sure PCH works by using function declared in PCH header.
 // CHECK:FunctionDecl 0x[[FOO:[0-9a-f]+]] <{{.*}}:2:1, line:4:1> line:2:8 imported used foo 'float2 (float2, float2)'
 // Make sure buffer defined in PCH works.
-// CHECK:VarDecl 0x{{[0-9a-f]+}} <line:6:1, col:17> col:17 imported Buf 'RWBuffer<float>':'hlsl::RWBuffer<>'
+// CHECK:VarDecl 0x{{[0-9a-f]+}} <line:6:1, col:17> col:17 imported Buf 'RWBuffer<float>'
 // Make sure declare a RWBuffer in current file works.
-// CHECK:VarDecl 0x{{[0-9a-f]+}} <{{.*}}:11:1, col:23> col:23 Buf2 'hlsl::RWBuffer<float>':'hlsl::RWBuffer<>'
+// CHECK:VarDecl 0x{{[0-9a-f]+}} <{{.*}}:11:1, col:23> col:23 Buf2 'hlsl::RWBuffer<float>'
 hlsl::RWBuffer<float> Buf2;
 
 float2 bar(float2 a, float2 b) {
diff --git a/clang/test/AST/HLSL/resource_binding_attr.hlsl b/clang/test/AST/HLSL/resource_binding_attr.hlsl
index 6836071971111..71900f2dbda55 100644
--- a/clang/test/AST/HLSL/resource_binding_attr.hlsl
+++ b/clang/test/AST/HLSL/resource_binding_attr.hlsl
@@ -23,15 +23,15 @@ float foo() {
   return a + b;
 }
 
-// CHECK: VarDecl 0x{{[0-9a-f]+}} <{{.*}}> col:17 UAV 'RWBuffer<float>':'hlsl::RWBuffer<>' callinit
-// CHECK-NEXT:-CXXConstructExpr 0x{{[0-9a-f]+}} <col:17> 'RWBuffer<float>':'hlsl::RWBuffer<>' 'void ()'
+// CHECK: VarDecl 0x{{[0-9a-f]+}} <{{.*}}> col:17 UAV 'RWBuffer<float>':'hlsl::RWBuffer<float>' callinit
+// CHECK-NEXT:-CXXConstructExpr 0x{{[0-9a-f]+}} <col:17> 'RWBuffer<float>':'hlsl::RWBuffer<float>' 'void ()'
 // CHECK-NEXT:-HLSLResourceBindingAttr 0x{{[0-9a-f]+}} <col:23> "u3" "space0"
 RWBuffer<float> UAV : register(u3);
 
-// CHECK: -VarDecl 0x{{[0-9a-f]+}} <{{.*}}> col:17 UAV1 'RWBuffer<float>':'hlsl::RWBuffer<>' callinit
-// CHECK-NEXT:-CXXConstructExpr 0x{{[0-9a-f]+}} <col:17> 'RWBuffer<float>':'hlsl::RWBuffer<>' 'void ()'
+// CHECK: -VarDecl 0x{{[0-9a-f]+}} <{{.*}}> col:17 UAV1 'RWBuffer<float>':'hlsl::RWBuffer<float>' callinit
+// CHECK-NEXT:-CXXConstructExpr 0x{{[0-9a-f]+}} <col:17> 'RWBuffer<float>':'hlsl::RWBuffer<float>' 'void ()'
 // CHECK-NEXT:-HLSLResourceBindingAttr 0x{{[0-9a-f]+}} <col:24> "u2" "space0"
-// CHECK-NEXT:-VarDecl 0x{{[0-9a-f]+}} <col:1, col:38> col:38 UAV2 'RWBuffer<float>':'hlsl::RWBuffer<>' callinit
-// CHECK-NEXT:-CXXConstructExpr 0x{{[0-9a-f]+}} <col:38> 'RWBuffer<float>':'hlsl::RWBuffer<>' 'void ()'
+// CHECK-NEXT:-VarDecl 0x{{[0-9a-f]+}} <col:1, col:38> col:38 UAV2 'RWBuffer<float>':'hlsl::RWBuffer<float>' callinit
+// CHECK-NEXT:-CXXConstructExpr 0x{{[0-9a-f]+}} <col:38> 'RWBuffer<float>':'hlsl::RWBuffer<float>' 'void ()'
 // CHECK-NEXT:-HLSLResourceBindingAttr 0x{{[0-9a-f]+}} <col:45> "u4" "space0"
 RWBuffer<float> UAV1 : register(u2), UAV2 : register(u4);
diff --git a/clang/test/SemaHLSL/BuiltIns/RWBuffers.hlsl b/clang/test/SemaHLSL/BuiltIns/RWBuffers.hlsl
index a9f6567aa00b8..7e79ae3bf005f 100644
--- a/clang/test/SemaHLSL/BuiltIns/RWBuffers.hlsl
+++ b/clang/test/SemaHLSL/BuiltIns/RWBuffers.hlsl
@@ -5,6 +5,14 @@ typedef vector<float, 3> float3;
 
 RWBuffer<float3> Buffer;
 
+// expected-error@+2 {{class template 'RWBuffer' requires template arguments}}
+// expected-note@*:* {{template declaration from hidden source: template <class element_type> class RWBuffer final}}
+RWBuffer BufferErr1;
+
+// expected-error@+2 {{too few template arguments for class template 'RWBuffer'}}
+// expected-note@*:* {{template declaration from hidden source: template <class element_type> class RWBuffer final}}
+RWBuffer<> BufferErr2;
+
 [numthreads(1,1,1)]
 void main() {
   (void)Buffer.h; // expected-error {{'h' is a private member of 'hlsl::RWBuffer<float __attribute__((ext_vector_type(3)))>'}}
diff --git a/clang/test/SemaHLSL/BuiltIns/vector-errors.hlsl b/clang/test/SemaHLSL/BuiltIns/vector-errors.hlsl
index d2598a57400b0..6aedb9304ed93 100644
--- a/clang/test/SemaHLSL/BuiltIns/vector-errors.hlsl
+++ b/clang/test/SemaHLSL/BuiltIns/vector-errors.hlsl
@@ -2,17 +2,16 @@
 
 // Some bad declarations
 hlsl::vector ShouldWorkSomeday; // expected-error{{use of alias template 'hlsl::vector' requires template arguments}}
+// expected-note@*:* {{template declaration from hidden source: template <class element = float, int element_count = 4> using vector = element __attribute__((ext_vector_type(element_count)))}}
 
 hlsl::vector<1> BadVec; // expected-error{{template argument for template type parameter must be a type}}
-// expected-note@*:* {{template is declared here}}
-// expected-note@*:* {{template parameter is declared here}}
-
+// expected-note@*:* {{template parameter from hidden source: class element = float}}
 
 hlsl::vector<int, float> AnotherBadVec; // expected-error{{template argument for non-type template parameter must be an expression}}
-// expected-note@*:* {{template parameter is declared here}}
+// expected-note@*:* {{template parameter from hidden source: int element_count = 4}}
 
 hlsl::vector<int, 2, 3> YABV; // expected-error{{too many template arguments for alias template 'vector'}}
-// expected-note@*:* {{template is declared here}}
+// expected-note@*:* {{template declaration from hidden source: template <class element = float, int element_count = 4> using vector = element __attribute__((ext_vector_type(element_count)))}}
 
 // This code is rejected by clang because clang puts the HLSL built-in types
 // into the HLSL namespace.