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defaults.go
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defaults.go
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package cfgtest
import (
"bufio"
"fmt"
"io"
"reflect"
"strings"
"github.com/pkg/errors"
)
// DocDefaultsOnly reads only the default values from a docs TOML file and decodes in to cfg.
// Fields without defaults will set to zero values.
func DocDefaultsOnly(r io.Reader, cfg any, decode func(io.Reader, any) error) error {
pr, pw := io.Pipe()
defer pr.Close()
go writeDefaults(r, pw)
if err := decode(pr, cfg); err != nil {
return errors.Wrapf(err, "failed to decode default core configuration")
}
// replace niled examples with zero values.
nilToZero(reflect.ValueOf(cfg))
return nil
}
// writeDefaults writes default lines from defaultsTOML to w.
func writeDefaults(r io.Reader, w *io.PipeWriter) {
defer w.Close()
s := bufio.NewScanner(r)
for s.Scan() {
t := s.Text()
// Skip comments and examples (which become zero values)
if strings.HasPrefix(t, "#") || strings.HasSuffix(t, "# Example") {
continue
}
if _, err := io.WriteString(w, t); err != nil {
w.CloseWithError(err)
}
if _, err := w.Write([]byte{'\n'}); err != nil {
w.CloseWithError(err)
}
}
if err := s.Err(); err != nil {
w.CloseWithError(fmt.Errorf("failed to scan core defaults: %v", err))
}
}
func nilToZero(val reflect.Value) {
if val.Kind() == reflect.Ptr {
if val.IsNil() {
t := val.Type().Elem()
val.Set(reflect.New(t))
}
if val.Type().Implements(textUnmarshalerType) {
return // don't descend inside - leave whole zero value
}
val = val.Elem()
}
switch val.Kind() {
case reflect.Struct:
if val.Type().Implements(textUnmarshalerType) {
return // skip values unmarshaled from strings
}
for i := 0; i < val.NumField(); i++ {
f := val.Field(i)
nilToZero(f)
}
return
case reflect.Map:
if !val.IsNil() {
for _, k := range val.MapKeys() {
nilToZero(val.MapIndex(k))
}
}
return
case reflect.Slice:
if !val.IsNil() {
for i := 0; i < val.Len(); i++ {
nilToZero(val.Index(i))
}
}
return
default:
return
}
}