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fix: allow env var to override non-zero struct values (#364) #365

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fix: allow env var to override non-zero struct values (#364) #365

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17 changes: 10 additions & 7 deletions env.go
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Original file line number Diff line number Diff line change
Expand Up @@ -502,12 +502,12 @@ func doParseSlice(ref reflect.Value, processField processFieldFn, opts Options)
}

func setField(refField reflect.Value, refTypeField reflect.StructField, opts Options, fieldParams FieldParams) error {
value, err := get(fieldParams, opts)
value, fromEnv, err := get(fieldParams, opts)
if err != nil {
return err
}

if value != "" && (!opts.SetDefaultsForZeroValuesOnly || refField.IsZero()) {
if fromEnv || (value != "" && (!opts.SetDefaultsForZeroValuesOnly || refField.IsZero())) {

@caarlos0 caarlos0 Oct 7, 2026

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[P2] Preserve the final nonempty-value guard

For an initialized integer field tagged env:"PORT,expand" and Environment: map[string]string{"PORT": "${MISSING}"}, expansion resolves to an empty string, but fromEnv remains true and this calls the integer parser with "", producing strconv.ParseInt: parsing "": invalid syntax. Loading an empty readable file through an integer ,file field has the same regression. Both occur with SetDefaultsForZeroValuesOnly disabled as well as enabled; the base skips empty resolved values and preserves the initialized field. Keep value != "" outside the override condition: value != "" && (fromEnv || !opts.SetDefaultsForZeroValuesOnly || refField.IsZero()). Add focused empty-expansion and empty-file tests under both option settings, asserting no error and preservation of the initialized integer.

return set(refField, refTypeField, value, opts.FuncMap)
}

Expand Down Expand Up @@ -593,7 +593,7 @@ func parseFieldParams(field reflect.StructField, opts Options) (FieldParams, err
return result, nil
}

func get(fieldParams FieldParams, opts Options) (val string, err error) {
func get(fieldParams FieldParams, opts Options) (val string, fromEnv bool, err error) {
var exists, isDefault bool

val, exists, isDefault = getOr(
Expand All @@ -602,6 +602,9 @@ func get(fieldParams FieldParams, opts Options) (val string, err error) {
fieldParams.HasDefaultValue,
opts.Environment,
)
if _, ok := opts.Environment[fieldParams.Key]; ok && val != "" {

@ZhuJincheng-git ZhuJincheng-git Sep 3, 2026

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I think we can just directly check isDefault here.

fromEnv = true
Comment on lines +605 to +606

@caarlos0 caarlos0 Oct 7, 2026

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[P2] Do not mark a fallback default as an environment value

With Username initialized to "root", tags env:"USERNAME" envDefault:"admin", Environment: map[string]string{"USERNAME": ""}, and SetDefaultsForZeroValuesOnly: true, this now replaces "root" with "admin". getOr selects the default and returns isDefault=true, but this check sees the existing key and the nonempty selected default, sets fromEnv=true, and bypasses default preservation. Derive provenance from the existing exists/isDefault results rather than key presence alone. Add a regression test for an explicitly empty environment variable asserting no error and preservation of the initialized value.

}

if fieldParams.Expand {
val = os.Expand(val, opts.getRawEnv)
Expand All @@ -614,18 +617,18 @@ func get(fieldParams FieldParams, opts Options) (val string, err error) {
}

if fieldParams.Required && !exists && fieldParams.OwnKey != "" {
return "", newVarIsNotSetError(fieldParams.Key)
return "", false, newVarIsNotSetError(fieldParams.Key)
}

if fieldParams.NotEmpty && val == "" {
return "", newEmptyVarError(fieldParams.Key)
return "", false, newEmptyVarError(fieldParams.Key)
}

if fieldParams.LoadFile && val != "" {
filename := val
val, err = getFromFile(filename)
if err != nil {
return "", newLoadFileContentError(filename, fieldParams.Key, err)
return "", false, newLoadFileContentError(filename, fieldParams.Key, err)
}
}

Expand All @@ -634,7 +637,7 @@ func get(fieldParams FieldParams, opts Options) (val string, err error) {
opts.OnSet(fieldParams.Key, val, isDefault)
}
}
return val, err
return val, fromEnv, err
}

// split the env tag's key into the expected key and desired option, if any.
Expand Down
15 changes: 15 additions & 0 deletions env_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2411,3 +2411,18 @@ func TestEnvBleed(t *testing.T) {
isEqual(t, "", cfg.Foo)
})
}

func TestParse_Bug364EnvVarOverridesStructValue(t *testing.T) {
t.Setenv("USERNAME", "user1")

type cfg struct {
Username string `env:"USERNAME" envDefault:"admin"`
}
c := cfg{Username: "root"}

isNoErr(t, ParseWithOptions(&c, Options{
SetDefaultsForZeroValuesOnly: true,
}))

isEqual(t, c.Username, "user1")
}