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Merge pull request #88 from vimeo/anonymous_field_flatten_mangler
anonymous field flatten mangler
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,117 @@ | ||
| package transform | ||
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|
||
| import ( | ||
| "reflect" | ||
| ) | ||
|
|
||
| // AnonymousFlattenMangler hoists the fields from the types of anonymous | ||
| // struct-fields into the parent type. (working around decoders/sources that | ||
| // are unaware of anonymous fields) | ||
| // Note: this mangler is unaware of TextUnmarshaler implementations (it's tricky to do right when flattening). | ||
| // It should be combined with the TextUnmarshalerMangler if the prefered | ||
| // handling is to mask the other fields in that struct with the TextUnmarshaler | ||
| // implementation. | ||
| type AnonymousFlattenMangler struct{} | ||
|
|
||
| // Mangle is called for every field in a struct, and maps that to one or more output fields. | ||
| // Implementations that desire to leave fields unchanged should return | ||
| // the argument unchanged. (particularly useful if taking advantage of | ||
| // recursive evaluation) | ||
| func (a AnonymousFlattenMangler) Mangle(sf reflect.StructField) ([]reflect.StructField, error) { | ||
| // If it's not an anonymous field, return it as-is | ||
| if !sf.Anonymous { | ||
| return []reflect.StructField{sf}, nil | ||
| } | ||
| // Note: TranslateType already skips unexported fields | ||
|
|
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| // anonymous/embedded fields can only be interfaces, pointers and structs | ||
| switch sf.Type.Kind() { | ||
| case reflect.Pointer: | ||
| // recurse with the pointer stripped off | ||
| sfInner := sf | ||
| sfInner.Type = sf.Type.Elem() | ||
| return a.Mangle(sfInner) | ||
| case reflect.Struct: | ||
| out := make([]reflect.StructField, 0, sf.Type.NumField()) | ||
| for i := 0; i < sf.Type.NumField(); i++ { | ||
| innerField := sf.Type.Field(i) | ||
| if !innerField.IsExported() { | ||
| // skip unexported fields | ||
| continue | ||
| } | ||
| out = append(out, innerField) | ||
| } | ||
|
|
||
| return out, nil | ||
| default: | ||
| // leave everything else alone (there's nothing to promote) | ||
| // this includes interfaces and all other non-struct and | ||
| // non-pointer-to-struct types. | ||
| return []reflect.StructField{sf}, nil | ||
| } | ||
| } | ||
|
|
||
| // bool return value indicates whether all fields are nil (and as such, a nil value should be returned for pointer-types) | ||
| func (a AnonymousFlattenMangler) unmangleStruct(sf reflect.StructField, fvs []FieldValueTuple) (reflect.Value, bool) { | ||
| out := reflect.New(sf.Type).Elem() | ||
| if len(fvs) == 0 { | ||
| // no fields made it, just return out. | ||
| return out, true | ||
| } | ||
| fvsIdx := 0 | ||
| allNil := true | ||
| for i := 0; i < sf.Type.NumField(); i++ { | ||
| oft := sf.Type.Field(i) | ||
| if oft.Name == fvs[fvsIdx].Field.Name { | ||
| out.Field(i).Set(fvs[fvsIdx].Value) | ||
| switch fvs[fvsIdx].Value.Kind() { | ||
| // check for nil-able types | ||
| case reflect.Pointer, reflect.Slice, reflect.Map, reflect.Interface, reflect.Chan: | ||
| if !fvs[fvsIdx].Value.IsZero() { | ||
| allNil = false | ||
| } | ||
| default: | ||
| // non-nilable field, just assume it's non-nil | ||
| // pointerification shold have made this nilable, though. | ||
| allNil = false | ||
| } | ||
| fvsIdx++ | ||
| } | ||
| } | ||
| return out, allNil | ||
| } | ||
|
|
||
| // Unmangle is called for every source-field->mangled-field | ||
| // mapping-set, with the mangled-field and its populated value set. The | ||
| // implementation of Unmangle should return a reflect.Value that will | ||
| // be used for the next mangler or final struct value) | ||
| // Returned reflect.Value should be convertible to the field's type. | ||
| func (a AnonymousFlattenMangler) Unmangle(sf reflect.StructField, fvs []FieldValueTuple) (reflect.Value, error) { | ||
| if !sf.Anonymous { | ||
| // not anonymous, just forward the single value | ||
| return fvs[0].Value, nil | ||
| } | ||
| switch sf.Type.Kind() { | ||
| case reflect.Pointer: | ||
| // It's a pointer. check for nil; strip off the pointer and recurse | ||
| msf := sf | ||
| msf.Type = sf.Type.Elem() | ||
| v, allNil := a.unmangleStruct(msf, fvs) | ||
| if allNil { | ||
| return reflect.Zero(sf.Type), nil | ||
| } | ||
| return v.Addr(), nil | ||
| case reflect.Struct: | ||
| out, _ := a.unmangleStruct(sf, fvs) | ||
| return out, nil | ||
| default: | ||
| // not a struct-typed anonymous field, just forward up the chain | ||
| return fvs[0].Value, nil | ||
| } | ||
| } | ||
|
|
||
| // ShouldRecurse is called after Mangle for each field so nested struct | ||
| // fields get iterated over after any transformation done by Mangle(). | ||
| func (a AnonymousFlattenMangler) ShouldRecurse(_ reflect.StructField) bool { | ||
| return true | ||
| } |
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