# Contributing to `nvim-treesitter`

First of all, thank you very much for contributing to `nvim-treesitter`.

If you haven't already, you should really come and reach out to us on our [gitter](https://gitter.im/nvim-treesitter/community?utm_source=share-link&utm_medium=link&utm_campaign=share-link)
room, so we can help you with any question you might have!

As you know, `nvim-treesitter` is roughly splitted in two parts :

- Parser configurations : for various things like `locals`, `highlights`
- What we like to call *modules* : tiny lua modules that provide a given feature, based on parser configurations

Depending on which part of the plugin you want to contribute to, please read the appropriate section.

## Style Checks and Tests

We haven't implemented any functional tests yet. Feel free to contribute.
However, we check code style with `luacheck`!
Please install luacheck and activate our `pre-push` hook to automatically check style before
every push:

```bash
luarocks install luacheck
ln -s ../../scripts/pre-push .git/hooks/pre-push
```

## Adding new modules

If you want to see a new functionality added to `nvim-treesitter` feel free to first open an issue
to that we can track our solution!
Thus far, there is basically two types of modules:

- Little modules (like `incremental selection`) that are built in `nvim-treesitter`, we call them
  `builtin modules`.
- Bigger modules (like `completion-treesitter`, or `nvim-tree-docs`), or modules that integrate
  with other plugins, that we call `remote modules`.

In any case, you can build your own module ! To help you started in the process, we have a template
repository designed to build new modules [here](https://github.com/nvim-treesitter/module-template).
Feel free to use it, and contact us over on our
[gitter](https://gitter.im/nvim-treesitter/community?utm_source=share-link&utm_medium=link&utm_campaign=share-link).

## Parser configurations

Contributing to parser configurations is basically modifying one of the `queries/*/*.scm`.
Each of these `scheme` files contains a *tree-sitter query* for a given purpose.
Before going any further, we highly suggest that you [read more about tree-sitter queries](https://tree-sitter.github.io/tree-sitter/using-parsers#pattern-matching-with-queries).

Each query has an appropriate name, which is then used by modules to extract data from the syntax tree.
For now two types of queries are used by `nvim-treesitter`:

- `highlights.scm` : used for syntax highlighting, using the `highlight` module.
- `locals.scm` : used to extract keyword definitions, scopes, references, etc, using the `locals` module.

For both of these types there is a *norm* you will have to follow so that features work fine.
Here are some global advices :

- If your language is listed [here](https://tree-sitter.github.io/tree-sitter/using-parsers#pattern-matching-with-queries),
  you can debug and experiment with your queries there.
- If not, you should consider installing the [tree-sitter cli](https://github.com/tree-sitter/tree-sitter/tree/master/cli),
  you should then be able to open a local playground using `tree-sitter build-wasm && tree-sitter web-ui` within the
  parsers repo.
- An Example of somewhat complex highlight queries can be found in queries/ruby/highlights.scm (Maintained by @TravonteD)

### Highlights

As languages differ quite a lot, here is a set of captures available to you when building a `highlights.scm` query.
One important thing to note is that many of these capture groups are not supported by `neovim` for now, and will not have any
effect on highlighting. We will work on improving highlighting in the near future though.

#### Misc

```
@comment
@error for error (ERROR` nodes.
@punctuation.delimiter for `;` `.` `,`
@punctuation.bracket for `()` or `{}`
```

Some captures are related to language injection (like markdown code blocks). As this is not supported by neovim yet, these
are optional and will not have any effect for now.

```
@embedded
@injection
  language
  content
```

#### Constants

```
@constant
  builtin
  macro
@string
  regex
  escape
@character
@number
@boolean
@float
```

#### Functions

```
@function
  builtin
  macro
@parameter

@method
@field or @property

@constructor
```

#### Keywords

```
@conditional
@repeat
@label for C/Lua-like labels
@operator
@keyword
  function
@exception
@include keywords for including modules (e.g. import/from in Python)

@type
    builtin
@structure
```

#### Variables
```
@variable
  builtin
```

#### Text

Mainly for markup languages.

```
@text
@text.strong
@text.emphasis
@text.underline
@text.title
@text.literal
@text.uri
```

### Locals
```
@definition for various definitions
  function
  method
  var
  macro
  type
  field
  namespace for modules or C++ namespaces
  import for imported names
  doc for documentation adjacent to a definition. E.g.
```

```scheme
  (comment)* @definition.doc
    (method_declaration
        name: (field_identifier) @definition.method)
```

```
@scope
@reference
```