Make all fields in gtk.TreeIter private.

With them non-private it's not possible to iterate with
the iterator. That is because the internal fields are
critical to the iteration.

internal/generate/field.go

@@ -61,3 +61,7 @@ func (f Field) generate(g *jen.Group) {
 
 	f.Type.generator.generateDeclaration(g, f.goVarName)
 }
+
+func (f *Field) mergeAddenda(addenda *Field) {
+	f.Private = addenda.Private
+}

internal/generate/fields.go

@@ -15,3 +15,21 @@ func (ff Fields) generate(g *jen.Group) {
 		f.generate(g)
 	}
 }
+
+func (ff Fields) forName(name string) *Field {
+	for _, field := range ff {
+		if field.Name == name {
+			return field
+		}
+	}
+
+	return nil
+}
+
+func (ff Fields) mergeAddenda(addenda Fields) {
+	for _, addendaField := range addenda {
+		if field := ff.forName(addendaField.Name); field != nil {
+			field.mergeAddenda(addendaField)
+		}
+	}
+}

internal/generate/record.go

@@ -69,6 +69,7 @@ func (r *Record) mergeAddenda(addenda *Record) {
 	r.Constructors.mergeAddenda(addenda.Constructors)
 	r.Functions.mergeAddenda(addenda.Functions)
 	r.Methods.mergeAddenda(addenda.Methods)
+	r.Fields.mergeAddenda(addenda.Fields)
 }
 
 func (r *Record) generate(g *jen.Group, version *Version) {

internal/gir-files/Gtk-3.0-addenda.gir

@@ -188,6 +188,14 @@
     <record name="TreePath">
       <method blacklist="true" c:identifier="gtk_tree_path_get_indices"/>
     </record>
+
+
+    <record name="TreeIter">
+        <field name="stamp" private="1"/>
+        <field name="user_data" private="1"/>
+        <field name="user_data2" private="1"/>
+        <field name="user_data3" private="1"/>
+    </record>
   </namespace>
 </repository>