Fix a bug in typeobj when a type field's name is the same as one of its inner...

type: change
description: |-
  Fix a bug in typeobj when a type field's name is the same as one of its inner fields

  This specifically came up with Comment (though it wasn't caught because an error
  wasn't being caught, that's fixed here as well). Prior to unmarshaling into the
  selected inner struct field, typeobj.UnmarshalYAML unmarshals into the outer
  struct in order to unmarshal all non-type fields. However, if one of the fields
  intended for the inner struct field has the same name as one of the type fields
  in the outer struct there would be a conflict at this point.

  The solution is to modify the type of the outer struct being unmarshaled into at
  this stage, so that all fields with type tags automatically have a `yaml:"-"`
  tag, and so are ignored by the yaml unmarshaler at this stage.
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  account: mediocregopher
mediocregopher 4 years ago
parent 3ec0908b32
commit 4389da48e4
  1. 2
  2. 6
  3. 56
  4. 15

@ -31,7 +31,7 @@ func (proj *Project) GetCommit(h plumbing.Hash) (c Commit, err error) {
} else if c.TreeObject, err = proj.GitRepo.TreeObject(c.Object.TreeHash); err != nil {
return c, fmt.Errorf("getting git tree object %q: %w",
c.Object.TreeHash, err)
} else if c.Payload.UnmarshalText([]byte(c.Object.Message)); err != nil {
} else if err = c.Payload.UnmarshalText([]byte(c.Object.Message)); err != nil {
return c, fmt.Errorf("decoding commit message: %w", err)
c.Hash = c.Object.Hash

@ -4,7 +4,6 @@ import (
@ -155,12 +154,7 @@ func (p *PayloadUnion) UnmarshalText(msg []byte) error {
if err := yaml.Unmarshal(msgBody, p); err != nil {
return fmt.Errorf("unmarshaling commit payload from yaml: %w", err)
} else if reflect.DeepEqual(*p, PayloadUnion{}) {
// a basic check, but worthwhile
return errors.New("commit message is malformed, could not unmarshal yaml object")
return nil

@ -30,6 +30,26 @@ func parseTag(tag string) tagInfo {
// structTypeWithYAMLTags takes a type of kind struct and returns that same
// type, except all fields with a "type" tag will also have a `yaml:"-"` tag
// attached.
func structTypeWithYAMLTags(typ reflect.Type) (reflect.Type, error) {
n := typ.NumField()
outFields := make([]reflect.StructField, n)
for i := 0; i < n; i++ {
field := typ.Field(i)
hasTypeTag := field.Tag.Get("type") != ""
if hasTypeTag && field.Tag.Get("yaml") != "" {
return nil, fmt.Errorf("field %s has yaml tag and type tag", field.Name)
} else if hasTypeTag {
field.Tag += ` yaml:"-"`
outFields[i] = field
return reflect.StructOf(outFields), nil
func findTypeField(val reflect.Value, targetTypeTag string) (reflect.Value, reflect.StructField, error) {
typ := val.Type()
@ -60,31 +80,39 @@ func findTypeField(val reflect.Value, targetTypeTag string) (reflect.Value, refl
// data into that inner field.
func UnmarshalYAML(i interface{}, unmarshal func(interface{}) error) error {
val := reflect.Indirect(reflect.ValueOf(i))
if !val.CanSet() {
return fmt.Errorf("cannot unmarshal into value of type %T", i)
if !val.CanSet() || val.Kind() != reflect.Struct {
return fmt.Errorf("cannot unmarshal into value of type %T: must be a struct pointer", i)
// create a copy of the struct type, with `yaml:"-"` tags added to all
// fields with `type:"..."` tags. If we didn't do this then there would be
// conflicts in the next step if a type field's name was the same as one of
// its inner field names.
valTypeCP, err := structTypeWithYAMLTags(val.Type())
if err != nil {
return fmt.Errorf("cannot unmarshal into value of type %T: %w", i, err)
// unmarshal in all non-typeobj fields. construct a type which wraps the
// given one, hiding its UnmarshalYAML method (if it has one), and unmarshal
// onto that directly. The "type" field is also unmarshaled at this stage.
valWrap := reflect.New(reflect.StructOf([]reflect.StructField{
Name: "Type",
Type: typeOfString,
Tag: `yaml:"type"`,
Name: "Val",
Type: val.Type(),
Tag: `yaml:",inline"`,
{Name: "Type", Type: typeOfString, Tag: `yaml:"type"`},
{Name: "Val", Type: valTypeCP, Tag: `yaml:",inline"`},
if err := unmarshal(valWrap.Interface()); err != nil {
return err
// necessary to set non-type fields into the original value
// set non-type fields into the original value
valWrapInnerVal := valWrap.Elem().Field(1)
for i := 0; i < valWrapInnerVal.NumField(); i++ {
fieldVal, fieldTyp := valWrapInnerVal.Field(i), valTypeCP.Field(i)
if fieldTyp.Tag.Get("type") != "" {
typeVal := valWrap.Elem().Field(0).String()
fieldVal, fieldTyp, err := findTypeField(val, typeVal)

@ -17,9 +17,15 @@ type bar struct {
B int `yaml:"b"`
// baz has a field of the same name as the type, which is tricky
type baz struct {
Baz int `yaml:"baz"`
type outer struct {
Foo foo `type:"foo"`
Bar *bar `type:"bar"`
Baz baz `type:"baz"`
Other string `yaml:"other_field,omitempty"`
@ -81,7 +87,7 @@ func TestTypeObj(t *testing.T) {
descr: "invalid type value",
str: "type: baz",
str: "type: INVALID",
expErr: "invalid type value",
expObj: outer{},
@ -106,6 +112,13 @@ func TestTypeObj(t *testing.T) {
expTypeTag: "foo",
expElem: foo{A: 1},
descr: "type is same as field name",
str: "type: baz\nbaz: 3",
expObj: outer{Baz: baz{Baz: 3}},
expTypeTag: "baz",
expElem: baz{Baz: 3},
for _, test := range tests {