nvf/docs/manual/hacking/guidelines.md

# Guidelines {#sec-guidelines}

If your contribution tightly follows the guidelines, then there is a good chance
it will be merged without too much trouble. Some of the guidelines will be
strictly enforced, others will remain as gentle nudges towards the correct
direction. As we have no automated system enforcing those guidelines, please try
to double check your changes before making your pull request in order to avoid
"faulty" code slipping by.

If you are uncertain how these rules affect the change you would like to make
then feel free to start a discussion in the
[discussions tab](https://github.com/NotAShelf/nvf/discussions) ideally (but not
necessarily) before you start developing.

## Adding Documentation {#sec-guidelines-documentation}

[Nixpkgs Flavoured Markdown]: https://github.com/NixOS/nixpkgs/blob/master/doc/README.md#syntax

Almost all changes warrant updates to the documentation: at the very least, you
must update the changelog. Both the manual and module options use
[Nixpkgs Flavoured Markdown].

The HTML version of this manual containing both the module option descriptions
and the documentation of **nvf** (such as this page) can be generated and opened
by typing the following in a shell within a clone of the **nvf** Git repository:

```console
$ nix build .#docs-html
$ xdg-open $PWD/result/share/doc/nvf/index.html
```

## Formatting Code {#sec-guidelines-formatting}

Make sure your code is formatted as described in
[code-style section](#sec-guidelines-code-style). To maintain consistency
throughout the project you are encouraged to browse through existing code and
adopt its style also in new code.

## Formatting Commits {#sec-guidelines-commit-message-style}

Similar to [code style guidelines](#sec-guidelines-code-style) we encourage a
consistent commit message format as described in
[commit style guidelines](#sec-guidelines-commit-style).

## Commit Style {#sec-guidelines-commit-style}

The commits in your pull request should be reasonably self-contained. Which
means each and every commit in a pull request should make sense both on its own
and in general context. That is, a second commit should not resolve an issue
that is introduced in an earlier commit. In particular, you will be asked to
amend any commit that introduces syntax errors or similar problems even if they
are fixed in a later commit.

The commit messages should follow the
[seven rules](https://chris.beams.io/posts/git-commit/#seven-rule), except for
"Capitalize the subject line". We also ask you to include the affected code
component or module in the first line. A commit message ideally, but not
necessarily, follow the given template from home-manager's own documentation

```
  {component}: {description}

  {long description}
```

where `{component}` refers to the code component (or module) your change
affects, `{description}` is a very brief description of your change, and
`{long description}` is an optional clarifying description. As a rare exception,
if there is no clear component, or your change affects many components, then the
`{component}` part is optional. See
[example commit message](#sec-guidelines-ex-commit-message) for a commit message
that fulfills these requirements.

## Example Commit {#sec-guidelines-ex-commit-message}

The commit
[69f8e47e9e74c8d3d060ca22e18246b7f7d988ef](https://github.com/nix-community/home-manager/commit/69f8e47e9e74c8d3d060ca22e18246b7f7d988ef)
in home-manager contains the following commit message.

```
starship: allow running in Emacs if vterm is used

The vterm buffer is backed by libvterm and can handle Starship prompts
without issues.
```

Similarly, if you are contributing to **nvf**, you would include the scope of
the commit followed by the description:

```
languages/ruby: init module

Adds a language module for Ruby, adds appropriate formatters and Treesitter grammars
```

Long description can be omitted if the change is too simple to warrant it. A
minor fix in spelling or a formatting change does not warrant long description,
however, a module addition or removal does as you would like to provide the
relevant context, i.e. the reasoning behind it, for your commit.

Finally, when adding a new module, say `modules/foo.nix`, we use the fixed
commit format `foo: add module`. You can, of course, still include a long
description if you wish.

In case of nested modules, i.e `modules/languages/java.nix` you are recommended
to contain the parent as well - for example `languages/java: some major change`.

## Code Style {#sec-guidelines-code-style}

### Treewide {#sec-code-style-treewide}

Keep lines at a reasonable width, ideally 80 characters or less. This also
applies to string literals and module descriptions and documentation.

### Nix {#sec-code-style-nix}

[alejandra]: https://github.com/kamadorueda/alejandra

**nvf** is formatted by the [alejandra] tool and the formatting is checked in
the pull request and push workflows. Run the `nix fmt` command inside the
project repository before submitting your pull request.

While Alejandra is mostly opinionated on how code looks after formatting,
certain changes are done at the user's discretion based on how the original code
was structured.

Please use one line code for attribute sets that contain only one subset. For
example:

```nix
# parent modules should always be unfolded
# which means module = { value = ... } instead of module.value = { ... }
module = {
  value = mkEnableOption "some description" // { default = true; }; # merges can be done inline where possible

    # same as parent modules, unfold submodules
    subModule = {
        # this is an option that contains more than one nested value
        # Note: try to be careful about the ordering of `mkOption` arguments.
        # General rule of thumb is to order from least to most likely to change.
        # This is, for most cases, type < default < description.
        # Example, if present, would be between default and description
        someOtherValue = mkOption {
            type = lib.types.bool;
            default = true;
            description = "Some other description";
        };
    };
}
```

If you move a line down after the merge operator, Alejandra will automatically
unfold the whole merged attrset for you, which we **do not** want.

```nix
module = {
  key = mkEnableOption "some description" // {
    default = true; # we want this to be inline
  }; # ...
}
```

For lists, it is mostly up to your own discretion how you want to format them,
but please try to unfold lists if they contain multiple items and especially if
they are to include comments.

```nix
# this is ok
acceptableList = [
  item1 # comment
  item2
  item3 # some other comment
  item4
];

# this is not ok
listToBeAvoided = [item1 item2 /* comment */ item3 item4];

# this is ok
acceptableList = [item1 item2];

# this is also ok if the list is expected to contain more elements
acceptableList= [
  item1
  item2
  # more items if needed...
];
```