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struct: return error instead of panic when MapTo receives a nil pointer (fixes #369) #383

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struct: return error instead of panic when MapTo receives a nil pointer (fixes #369) #383

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e916782
struct: return error instead of panic when MapTo receives a nil pointer
May 9, 2026
621bdad
struct: auto-initialize nil pointers in mapToField, fix slice of poin…
May 9, 2026
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11 changes: 10 additions & 1 deletion struct.go
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Original file line number Diff line number Diff line change
Expand Up @@ -278,9 +278,18 @@ func parseTagOptions(tag string) (rawName string, omitEmpty bool, allowShadow bo
// mapToField maps the given value to the matching field of the given section.
// The sectionIndex is the index (if non unique sections are enabled) to which the value should be added.
func (s *Section) mapToField(val reflect.Value, isStrict bool, sectionIndex int, sectionName string) error {
if val.Kind() == reflect.Pointer {
for val.Kind() == reflect.Pointer {
if val.IsNil() {
if !val.CanSet() {
return fmt.Errorf("cannot initialize nil pointer: value is not settable")
}
val.Set(reflect.New(val.Type().Elem()))
}
val = val.Elem()
}
if !val.IsValid() {
return fmt.Errorf("cannot map to invalid value")
}
typ := val.Type()

for i := 0; i < typ.NumField(); i++ {
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44 changes: 44 additions & 0 deletions struct_test.go
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Expand Up @@ -385,6 +385,50 @@ names=alice, bruce`))
})
}

// Regression test for https://github.com/go-ini/ini/issues/370:
// Mapping non-unique sections into a slice of struct pointers ([]*T) must
// not panic.
func Test_MapToSliceOfStructPointers(t *testing.T) {
const data = `[Peer]
PublicKey = key1
[Peer]
PublicKey = key2
`
type Peer struct {
PublicKey string `ini:"PublicKey"`
}
type Config struct {
Peers []*Peer `ini:"Peer,nonunique"`
}
f, err := LoadSources(LoadOptions{AllowNonUniqueSections: true}, []byte(data))
assert.NoError(t, err)
cfg := new(Config)
assert.NoError(t, f.MapTo(cfg))
assert.Len(t, cfg.Peers, 2)
if len(cfg.Peers) == 2 {
assert.Equal(t, "key1", cfg.Peers[0].PublicKey)
assert.Equal(t, "key2", cfg.Peers[1].PublicKey)
}
}

// Regression test for https://github.com/go-ini/ini/issues/369 and #370:
// MapTo with a nil struct pointer must not panic; it should auto-initialize
// the pointer (analogous to encoding/json behaviour) and populate the struct.
func Test_MapToNilPointer(t *testing.T) {
f, err := Load([]byte("user = alice\npass = secret\n"))
assert.NoError(t, err)

type S struct {
User string `ini:"user"`
Pass string `ini:"pass"`
}
var s *S
assert.NoError(t, f.MapTo(&s), "MapTo with nil pointer should not return an error")
assert.NotNil(t, s, "nil pointer should have been initialized by MapTo")
assert.Equal(t, "alice", s.User)
assert.Equal(t, "secret", s.Pass)
}

func Test_MapToStructNonUniqueSections(t *testing.T) {
t.Run("map to struct non unique", func(t *testing.T) {
t.Run("map file to struct non unique", func(t *testing.T) {
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