feat(dotenv): Adding support for dotenv files

[chickencoding123]

This adds support for dotenv file format. It is accomplished by using dotenvy crate. There's an open issue asking for this feature here #16.

[coveralls]

Pull Request Test Coverage Report for Build 18750157020

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• 0 of 0 changed or added relevant lines in 0 files are covered.
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Change from base Build 18169995909:	0.0%
Covered Lines:	950
Relevant Lines:	1465

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💛 - Coveralls

[epage]

Does this work as another FileFormat / Source? I suspect there is a lot of design overlap with Environment that we'd want to make this functionality on that.

[chickencoding123]

This is another FileFormat. You can see the usage from the tests (added snippet for ref. here). It is similar to existing file formats. Also dotenvy dependency will take care of the overlap, if any. However I ensured OS env take precedence as per existing file formats.

 let s = Config::builder()
        .add_source(config::File::from_str(
            r#"
                FOO=bar
                BAZ=qux
            "#,
            config::FileFormat::Dotenv,
        ))
        .build()
        .unwrap();

[epage]

FYI resolving conversations that aren't ready for it can make PR reviews more difficult on maintainers. You should be pretty confident that you understood the concern and responded to it as the maintainer expected to resolve it. That was not the case here.

Some traits of dotenv are

• Stringly typed (so is ini)
• Unstructured

Both of these characteristics are shared with Environment which has a lot of functionality for solving these problems. In fact, this is another form of environment variables! The only difference is it also shares some of the file loading characteristics of file formats.

[epage]

I've raised this (and other questions) at #16 (comment) as I prefer to work out high level designs in Issues rather than PRs.

[epage]

Feel free to modify your commits for how they should be merged

[epage]

This should not be doing manual layering, that is what the ConfigBuilder is for.

[chickencoding123]

Dotenvy overrides OS var which is inconsistent with existing FileFormat in this crate. Manual layering is appealing here because file formats sit below ConfigBuilder in the hierarchy. Coupling a ConfigBuilder inside a file format will lead to difficult refactoring in the future.

I think for the purposes of this specific file format, simple env override should suffice?

[epage]

Manual layering is appealing here because file formats sit below ConfigBuilder in the hierarchy. Coupling a ConfigBuilder inside a file format will lead to difficult refactoring in the future.

Environment and each File are manually added as sources and the user has control over the precedence order. However we support DotEnv, it will be similar, so we don't need to do this here. If we did,. it would belong in Environment which is what is handling the OS vars.