Values are not loaded from environment with SetDefaultsForZeroValuesOnly

[dlmartens]

The change introduced in 2be9960 causes values to no longer load from the environment in the presence of SetDefaultsForZeroValuesOnly: true and a non-zero value for the corresponding field.

The following is a quick example to recreate the problem:

type Config struct {
	Username string `env:"USERNAME" envDefault:"admin"`
}
cfg := Config{Username: "root"}
err := env.ParseWithOptions(&cfg, env.Options{
	Environment:                  map[string]string{"USERNAME": "user1"},
	SetDefaultsForZeroValuesOnly: true,
})
if err != nil {
	fmt.Println(err)
	return
}
fmt.Printf("%+v", cfg) // prints `{Username:root}`, but should print `{Username:user1}`

The relevant logic is here:

env/env.go

Lines 510 to 512 in 56a09d2

	if value != "" && (!opts.SetDefaultsForZeroValuesOnly || refField.IsZero()) {
	return set(refField, refTypeField, value, opts.FuncMap)
	}

It does not check to ensure that value was loaded from envDefault rather than from the actual environment.

Thank you for the great library!

[jyr94]

Hi @dlmartens ! I'd like to contribute and take a look at this issue.

Just to clarify: even when SetDefaultsForZeroValuesOnly is true, environment variables should still override struct values, right?

Only envDefault should be skipped for non-zero fields?

If so, I'm happy to work on this with a test and a fix.

Tagging @caarlos0 as maintainer for confirmation — thanks!

[dlmartens]

In short, yes, I believe even when SetDefaultsForZeroValuesOnly is true, environment variables should still override struct values.

Documentation for the SetDefaultsForZeroValuesOnly flag:

// SetDefaultsForZeroValuesOnly defines whether to set defaults for zero values
// If the `env` variable for the value is not set
// and `envDefault` is set
// and the value is not a zero value for the the type
// and SetDefaultsForZeroValuesOnly=true
// the value from `envDefault` will be ignored
// Usefull for mixing default values from `envDefault` and struct initialization

https://github.com/caarlos0/env/blob/56a09d295d9321b1f3b537fd23df1527011cd83d/env.go#L165C2-L171C82

My understanding is that means the flag should only apply when the value is not present in the environment. Values from the environment should be loaded regardless of how we set defaults (zero values only vs. any value) when a value is not present in the environment.

It looks like the underlying problem is the get function does not return whether a value was loaded from the environment or from envDefault. If it distinguished between the two, then setField could be updated to always call set when a non-empty string value is loaded from the environment.

[jyr94]

Hi! I've submitted a PR to address this: #365

@caarlos0 feel free to review when you have time 🙌

[kukymbr]

Hi

I'm facing this issue too, it's really seems like an unexpected behavior.