groot/rdict: add r/w-streamer+type handling for TString

groot/rdict/type.go

@@ -29,14 +29,29 @@ func TypeFromSI(ctx rbytes.StreamerInfoContext, si rbytes.StreamerInfo) (reflect
 	}
 
 	switch {
+	case name == "TString":
+		if len(si.Elements()) == 0 {
+			sinfo := si.(*StreamerInfo)
+			sinfo.elems = append(sinfo.elems, &StreamerBasicType{
+				StreamerElement: Element{
+					Name:   *rbase.NewNamed("This", ""),
+					Type:   rmeta.TString,
+					Size:   25,
+					MaxIdx: [5]int32{0, 0, 0, 0, 0},
+					EName:  "TString",
+				}.New(),
+			})
+		}
+		return gotypes[reflect.String], nil
+
 	case name == "string", name == "std::string":
 		if len(si.Elements()) == 0 {
 			// fix for old (v=2) streamer for string
 			sinfo := si.(*StreamerInfo)
 			sinfo.elems = append(sinfo.elems, &StreamerSTLstring{
 				StreamerSTL: StreamerSTL{
 					StreamerElement: Element{
-						Name:   *rbase.NewNamed("This", ""),
+						Name:   *rbase.NewNamed("This", "Used to call the proper TStreamerInfo case"),
 						Type:   rmeta.STLstring,
 						Size:   32,
 						MaxIdx: [5]int32{0, 0, 0, 0, 0},

groot/rdict/type_test.go

@@ -85,6 +85,18 @@ func TestTypeFromSI(t *testing.T) {
 			}(),
 			want: reflect.TypeOf((*rbase.Object)(nil)).Elem(),
 		},
+		{
+			name: "TString",
+			si: func() rbytes.StreamerInfo {
+				const name = "TString"
+				si, ok := rdict.StreamerInfos.Get(name, -1)
+				if !ok {
+					t.Fatalf("could not load streamer for %q", name)
+				}
+				return si
+			}(),
+			want: reflect.TypeOf((*string)(nil)).Elem(),
+		},
 		{
 			name: "TNamed",
 			si: func() rbytes.StreamerInfo {

groot/rdict/z_tstring_streamer.go

@@ -0,0 +1,36 @@
+// Copyright ©2022 The go-hep Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package rdict
+
+import (
+	"fmt"
+
+	"go-hep.org/x/hep/groot/rbase"
+	"go-hep.org/x/hep/groot/rmeta"
+)
+
+func init() {
+	si, ok := StreamerInfos.Get("TString", -1)
+	if !ok {
+		panic(fmt.Errorf("rdict: could not get streamer info for TString"))
+	}
+	if len(si.Elements()) != 0 {
+		return
+	}
+
+	// FIXME(sbinet): the ROOT/C++ streamer for TString is a simple placeholder.
+	// but groot relies on the actual list of StreamerElements to generate the r/w-streaming code.
+	// So, apply this "regularization" and hope for the best.
+	sinfo := si.(*StreamerInfo)
+	sinfo.elems = append(sinfo.elems, &StreamerBasicType{
+		StreamerElement: Element{
+			Name:   *rbase.NewNamed("This", "Used to call the proper TStreamerInfo case"),
+			Type:   rmeta.TString,
+			Size:   25,
+			MaxIdx: [5]int32{0, 0, 0, 0, 0},
+			EName:  "TString",
+		}.New(),
+	})
+}