Vector fields are overwritten instead of merged

[dhruvkb]

Consider the following config.

struct Conf {
	nums: Vec<i32>
}

This is built and given two config files.

# a.yml
nums:
- 1
- 2

# b.yml
nums:
- 3
- 4

The output of this configuration is that nums has only [3, 4]. Vectors should be merged, and nums should contain [1, 2, 3, 4].

[matthiasbeyer]

Hi,

thanks for your report. I don't think lists should be merged necessarily, but I see that in some instances, users might want to merge lists.

[dhruvkb]

If not the predominant default behaviour, at least an option or workaround to merge lists would be great to have. Thanks for considering this.

[n8henrie]

I would also be interested in this as an option.

In my case, I'm thinking of an option, for example a vec of PathBuf, that may have some defaults optionally set in a config file, but an additional path may also be specified in an environment variable.

[epage]

Cargo runs into the opposite with its config design. It always assumes lists should be appended but that doesn't work well for a command and we had to hard code in the config merging the names of the fields that should overwrite rather than append.

A big question in this is how should the behavior be configured?