proc: automatically dereference interfaces on member access

If 'iv' is an interface variable with a struct as a concrete value let
'iv.A' evaluate to the access to field 'A' of the concrete value of
'iv'.

pkg/proc/variables.go

@@ -670,6 +670,11 @@ func (v *Variable) structMember(memberName string) (*Variable, error) {
 	case reflect.Chan:
 		v = v.clone()
 		v.RealType = resolveTypedef(&(v.RealType.(*godwarf.ChanType).TypedefType))
+	case reflect.Interface:
+		v.loadInterface(0, false, LoadConfig{})
+		if len(v.Children) > 0 {
+			v = &v.Children[0]
+		}
 	}
 	structVar := v.maybeDereference()
 	structVar.Name = v.Name

service/test/variables_test.go

@@ -552,6 +552,8 @@ func TestEvalExpression(t *testing.T) {
 		{"err2", true, "error(*main.bstruct) *{a: main.astruct {A: 1, B: 2}}", "error(*main.bstruct) 0x…", "error", nil},
 		{"errnil", true, "error nil", "error nil", "error", nil},
 		{"iface1", true, "interface {}(*main.astruct) *{A: 1, B: 2}", "interface {}(*main.astruct) 0x…", "interface {}", nil},
+		{"iface1.A", false, "1", "1", "int", nil},
+		{"iface1.B", false, "2", "2", "int", nil},
 		{"iface2", true, "interface {}(string) \"test\"", "interface {}(string) \"test\"", "interface {}", nil},
 		{"iface3", true, "interface {}(map[string]go/constant.Value) []", "interface {}(map[string]go/constant.Value) []", "interface {}", nil},
 		{"iface4", true, "interface {}([]go/constant.Value) [4]", "interface {}([]go/constant.Value) [...]", "interface {}", nil},