# `tree-sitter-fluent`

`tree-sitter-fluent` is an error-tolerant Tree-sitter grammar for Project Fluent FTL. It supports editors, linting, incremental parsing, and source-preserving tools.

## Build the grammar with Nix

```bash
nix build .#tree-sitter-fluent
```

The package contains:

```text
result/
├── parser
├── lib/
│   └── libtree-sitter-fluent.so -> ../parser
├── queries/
│   └── highlights.scm
└── tree-sitter.json
```

`parser` is the compiled shared library in the layout used by Nixpkgs Tree-sitter grammar packages. The `lib` link uses the platform’s shared-library extension—`.so` on Linux—and lets Emacs find the same library directly.

## Use the Rust bindings

The workspace crate exports a `tree-sitter-language` function and the generated node and highlight metadata:

```rust
use tree_sitter::Parser;

let mut parser = Parser::new();
let language = tree_sitter_fluent::LANGUAGE.into();
parser.set_language(&language)?;
```

The public constants are:

| Constant | Contents |
| --- | --- |
| `LANGUAGE` | Language function for `Parser::set_language` |
| `NODE_TYPES` | Generated `src/node-types.json` |
| `HIGHLIGHTS_QUERY` | `queries/highlights.scm` |

An external Cargo project can depend on the repository directly:

```toml
[dependencies]
tree-sitter = "0.25"
tree-sitter-fluent = { git = "https://github.com/outskirtslabs/fluent-tooling" }
```

## Grammar behavior

The CST exposes default variants as `default_variant` nodes, retains malformed regions as Tree-sitter errors, and recovers later valid entries. The grammar accepts LF, CRLF, and lone CR line endings, negative numeric literals, EOF comments, unindented block placeables, and deeply nested selectors.

The highlight query covers the syntax used by `fluent-ts-mode` and other Tree-sitter consumers. Tests compile the query against the generated grammar to keep captures synchronized with node types.

## Grammar sources

The repository keeps generated C sources under `src/` so consumers can compile the grammar without running the Tree-sitter generator:

| Path | Purpose |
| --- | --- |
| `grammar.js` | Authoritative grammar definition |
| `tree-sitter.json` | Grammar name, version, file types, and repository metadata |
| `src/parser.c` | Parser generated from `grammar.js` |
| `src/scanner.c` | Handwritten external scanner |
| `src/node-types.json` | Generated named-node metadata |
| `queries/highlights.scm` | Syntax-highlight captures |

Tree-sitter build tools conventionally look for `src/parser.c` and optionally `src/scanner.c` or `src/scanner.cc`. Emacs’s built-in installer follows that layout when it builds this repository’s public grammar recipe.

After editing `grammar.js`, regenerate the checked-in parser as described in the [development guide](development.adoc).