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starlark.go
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starlark.go
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package scriptlet
import (
"fmt"
"reflect"
"sort"
"strings"
"go.starlark.net/starlark"
)
// starlarkObject wraps a starlark.Dict and is used to provide custom object types to the Starlark scriptlets.
// This implements the starlark.HasAttrs interface.
type starlarkObject struct {
d *starlark.Dict
typeName string
}
func (s *starlarkObject) Type() string {
return s.typeName
}
func (s *starlarkObject) String() string {
return s.d.String()
}
func (s *starlarkObject) Freeze() {
}
func (s *starlarkObject) Hash() (uint32, error) {
return 0, fmt.Errorf("Unhashable type %s", s.Type())
}
func (s *starlarkObject) Truth() starlark.Bool {
return starlark.True
}
func (s *starlarkObject) AttrNames() []string {
keys := s.d.Keys()
keyNames := make([]string, 0, len(keys))
for _, k := range keys {
keyNames = append(keyNames, k.String())
}
return keyNames
}
func (s *starlarkObject) Attr(name string) (starlark.Value, error) {
field, found, err := s.d.Get(starlark.String(name))
if err != nil {
return nil, err
}
if !found {
return nil, fmt.Errorf("Invalid field %q", name)
}
return field, nil
}
// StarlarkMarshal converts input to a starlark Value.
// It only includes exported struct fields, and uses the "json" tag for field names.
func StarlarkMarshal(input any) (starlark.Value, error) {
return starlarkMarshal(input, nil)
}
// starlarkMarshal converts input to a starlark Value.
// It only includes exported struct fields, and uses the "json" tag for field names.
// Takes optional parent Starlark dictionary which will be used to set fields from anonymous (embedded) structs
// in to the parent struct.
func starlarkMarshal(input any, parent *starlark.Dict) (starlark.Value, error) {
if input == nil {
return starlark.None, nil
}
sv, ok := input.(starlark.Value)
if ok {
return sv, nil
}
var err error
v := reflect.ValueOf(input)
switch v.Type().Kind() {
case reflect.String:
sv = starlark.String(v.String())
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
sv = starlark.MakeInt(int(v.Int()))
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
sv = starlark.MakeUint(uint(v.Uint()))
case reflect.Float32, reflect.Float64:
sv = starlark.Float(v.Float())
case reflect.Bool:
sv = starlark.Bool(v.Bool())
case reflect.Array, reflect.Slice:
vlen := v.Len()
listElems := make([]starlark.Value, 0, vlen)
for i := 0; i < vlen; i++ {
lv, err := StarlarkMarshal(v.Index(i).Interface())
if err != nil {
return nil, err
}
listElems = append(listElems, lv)
}
sv = starlark.NewList(listElems)
case reflect.Map:
mKeys := v.MapKeys()
d := starlark.NewDict(len(mKeys))
if v.Type().Key().Kind() != reflect.String {
return nil, fmt.Errorf("Only string keys are supported, found %s", v.Type().Key().Kind())
}
sort.Slice(mKeys, func(i, j int) bool {
return mKeys[i].String() < mKeys[j].String()
})
for _, k := range mKeys {
mv := v.MapIndex(k)
dv, err := StarlarkMarshal(mv.Interface())
if err != nil {
return nil, err
}
err = d.SetKey(starlark.String(k.String()), dv)
if err != nil {
return nil, fmt.Errorf("Failed setting map key %q to %v: %w", k.String(), dv, err)
}
}
sv = d
case reflect.Struct:
fieldCount := v.Type().NumField()
d := parent
if d == nil {
d = starlark.NewDict(fieldCount)
}
for i := 0; i < fieldCount; i++ {
field := v.Type().Field(i)
fieldValue := v.Field(i)
if !field.IsExported() {
continue
}
if field.Anonymous && fieldValue.Kind() == reflect.Struct {
// If anonymous struct field's value is another struct then pass the the current
// starlark dictionary to starlarkMarshal so its fields will be set on the parent.
_, err = starlarkMarshal(fieldValue.Interface(), d)
if err != nil {
return nil, err
}
} else {
dv, err := StarlarkMarshal(fieldValue.Interface())
if err != nil {
return nil, err
}
key, _, _ := strings.Cut(field.Tag.Get("json"), ",")
if key == "" {
key = field.Name
}
err = d.SetKey(starlark.String(key), dv)
if err != nil {
return nil, fmt.Errorf("Failed setting struct field %q to %v: %w", key, dv, err)
}
}
}
// Only convert the top-level struct to a Starlark object.
if parent == nil {
ss := starlarkObject{
d: d,
typeName: v.Type().Name(),
}
sv = &ss
} else {
sv = d
}
case reflect.Pointer:
if v.IsZero() {
sv = starlark.None
} else {
sv, err = StarlarkMarshal(v.Elem().Interface())
if err != nil {
return nil, err
}
}
}
if sv == nil {
return nil, fmt.Errorf("Unrecognised type %v for value %+v", v.Type(), v.Interface())
}
return sv, nil
}