feat(book/src/languages.md) (#979)

* feat(book/src/languages.md)

Add a section in the book about language-specific settings and the languages.toml file.

* Update book/src/languages.md

Co-authored-by: Gokul Soumya <gokulps15@gmail.com>

* feat(book/src/guides/adding_languages.md)

Add book section on adding a new language to the compile-time/root languages.toml file.

* Update book/src/guides/adding_languages.md

Co-authored-by: Blaž Hrastnik <blaz@mxxn.io>

* Update book/src/guides/adding_languages.md

Co-authored-by: Blaž Hrastnik <blaz@mxxn.io>

* refactor(revise book/src/languages.md)

Change the book page on language settings to match suggestions by archseer and mention both toml files.

Co-authored-by: Gokul Soumya <gokulps15@gmail.com>
Co-authored-by: Blaž Hrastnik <blaz@mxxn.io>

1 files changed, 52 insertions, 0 deletions

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+# Adding languages
+
+## Submodules
+
+To add a new langauge, you should first add a tree-sitter submodule. To do this, you can run the command
+```sh
+$ git submodule add -f <repository> helix-syntax/languages/tree-sitter-<name>
+```
+For example, to add tree-sitter-ocaml you would run
+```sh
+$ git submodule add -f https://github.com/tree-sitter/tree-sitter-ocaml helix-syntax/languages/tree-sitter-ocaml
+```
+Make sure the submodule is shallow by doing
+```sh
+git config -f .gitmodules submodule.helix-syntax/languages/tree-sitter-<name>.shallow true
+```
+
+or you can manually add `shallow = true` to `.gitmodules`.
+
+## languages.toml
+
+Next, you need to add the language to the `languages.toml` found in the root of the repository; this `languages.toml` file is included at compilation time, and is distinct from the `language.toml` file in the user's [configuration directory](../configuration.md).
+
+These are the available keys and descriptions for the file.
+
+| Key           | Description                                                   |
+| ----          | -----------                                                   |
+| name          | The name of the language                                      |
+| scope         | A string like `source.js` that identifies the language. Currently, we strive to match the scope names used by popular TextMate grammars and by the Linguist library. Usually `source.<name>` or `text.<name>` in case of markup languages |
+| injection-regex | regex pattern that will be tested against a language name in order to determine whether this language should be used for a potential language injection site. [link](https://tree-sitter.github.io/tree-sitter/syntax-highlighting#language-injection) |
+| file-types    | The filetypes of the language, for example `["yml", "yaml"]`  |
+| roots         | A set of marker files to look for when trying to find the workspace root. For example `Cargo.lock`, `yarn.lock` |
+| auto-format   | Whether to autoformat this language when saving               |
+| comment-token | The token to use as a comment-token                           |
+| indent        | The indent to use. Has sub keys `tab-width` and `unit`            |
+| config        | Language server configuration                                 |
+
+## Queries
+
+For a language to have syntax-highlighting and indentation among other things, you have to add queries. Add a directory for your language with the path `runtime/queries/<name>/`. The tree-sitter [website](https://tree-sitter.github.io/tree-sitter/syntax-highlighting#queries) gives more info on how to write queries.
+
+## Common Issues
+
+- If you get errors when building after switching branches, you may have to remove or update tree-sitter submodules. You can update submodules by running
+```sh
+$ git submodule update --init
+```
+- Make sure to not use the `--remote` flag. To remove submodules look inside the `.gitmodules` and remove directories that are not present inside of it.
+
+- If a parser is segfaulting or you want to remove the parser, make sure to remove the submodule *and* the compiled parser in `runtime/grammar/<name>.so`
+
+- The indents query is `indents.toml`, *not* `indents.scm`. See [this](https://github.com/helix-editor/helix/issues/114) issue for more information.