Inconsistent time conversion

[mimol91]

Look on this small go code

package main

import (
	"fmt"
	"time"

	"github.com/mitchellh/mapstructure"
)

type Record struct {
	Date   time.Time    `json:"date"`
	DateP  *time.Time   `json:"datep"`
	Dates  []time.Time  `json:"dates"`
	DatesP []*time.Time `json:"datesp"`
}

func main() {
	now := time.Now()
	record := Record{
		Date:   now,
		DateP:  &now,
		Dates:  []time.Time{now},
		DatesP: []*time.Time{&now},
	}

	var result map[string]any
	decoder, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{
		Result:  &result,
		TagName: "json",
	})
	if err != nil {
		panic(err)
	}
	if err := decoder.Decode(record); err != nil {
		panic(err)
	}
	fmt.Println(result)
}

Result map has all fields except (date) correctly set.

map[
date:map[] 
datep:2026-01-12 15:07:35.44162 +0400 +04 m=+0.000086376 
dates:[2026-01-12 15:07:35.44162 +0400 +04 m=+0.000086376] 
datesp:[2026-01-12 15:07:35.44162 +0400 +04 m=+0.000086376]
]

It seems to be counter intuitive

[sagikazarmark]

Good point!

Unfortunately, the solution is not obvious: we could enforce a fix format by default, but I doubt it would play well.

I'd suggest adding a decode hook for converting time to string or whatever format you need.

For example:

  func TimeToStringHookFunc(layout string) DecodeHookFunc {
      return func(f reflect.Type, t reflect.Type, data any) (any, error) {
          // Handle both time.Time and *time.Time
          if t.Kind() == reflect.String || t.Kind() == reflect.Interface {
              if tm, ok := data.(time.Time); ok {
                  return tm.Format(layout), nil
              }
              if tm, ok := data.(*time.Time); ok && tm != nil {
                  return tm.Format(layout), nil
              }
          }
          return data, nil
      }
  }

This way you can convert time into any representation you need.

[iamtakingiteasy]

The issue is not a time format, but that time.Time being a struct is forced to be decoded as map[string]any before hook has any chance to affect it. To make it work, something like #43 is necessary, dispatching to hooks before map[string]any output is created, preferably regardless of v type, unlike in closed merge request.