@willbooster/tree-sitter-kotlin

Kotlin grammar for tree-sitter, forked from tree-sitter-grammars/tree-sitter-kotlin. We are grateful to its authors and contributors. This is not an official release of that project.

This fork fixes parsing bugs and raises conformance with the Kotlin grammar.

Usage

The npm package ships tree-sitter-kotlin.wasm for @willbooster/web-tree-sitter, which runs in Node.js, Bun, browsers, and Cloudflare Workers.

In Node.js and Bun:

import { fileURLToPath } from 'node:url';
import { Language, Parser } from '@willbooster/web-tree-sitter';

await Parser.init();
const parser = new Parser();
const wasmPath = fileURLToPath(import.meta.resolve('@willbooster/tree-sitter-kotlin/tree-sitter-kotlin.wasm'));
parser.setLanguage(await Language.load(wasmPath));
const tree = parser.parse('fun main() = println("Hello")\n');

In browsers, load both .wasm files by URL. With Vite:

import { Language, Parser } from '@willbooster/web-tree-sitter';
import runtimeUrl from '@willbooster/web-tree-sitter/web-tree-sitter.wasm?url';
import kotlinUrl from '@willbooster/tree-sitter-kotlin/tree-sitter-kotlin.wasm?url';

await Parser.init({ locateFile: () => runtimeUrl });
const parser = new Parser();
parser.setLanguage(await Language.load(kotlinUrl));

In Cloudflare Workers, which do not allow compiling Wasm at run time, import both .wasm files as modules (with or without Node.js compatibility):

import { Language, Parser } from '@willbooster/web-tree-sitter';
import runtime from '@willbooster/web-tree-sitter/web-tree-sitter.wasm';
import kotlin from '@willbooster/tree-sitter-kotlin/tree-sitter-kotlin.wasm';

await Parser.init({ wasmModule: runtime });
const parser = new Parser();
parser.setLanguage(await Language.load(kotlin));

The package also ships the node types in src/node-types.json.

In Rust, depend on the crate:

[dependencies]
tree-sitter = "0.27"
tree-sitter-kotlin = { package = "willbooster-tree-sitter-kotlin", version = "1.2" }

let mut parser = tree_sitter::Parser::new();
parser.set_language(&tree_sitter_kotlin::LANGUAGE.into())?;

Development

mise install
bun install --frozen-lockfile
bun run test/ci-setup
bun run build/ci
bun run test
script/parse-examples
cargo test

bun run test runs:

• the corpus in test/corpus, with the native build and with the Wasm build (the first run downloads the WASI SDK);
• an incremental-parsing check (test/unit/incremental.test.ts): tree-sitter fuzz edits each corpus case at random, reparses it, undoes the edits, and reparses again. TREE_SITTER_SEED, TREE_SITTER_ITERATIONS, and TREE_SITTER_EDITS run other or more edits;
• a check that real-world Kotlin files cloned into examples/ fail to parse exactly as listed in script/known-failures.txt. The first run clones them. The example repositories are pinned to commits in script/parse-examples. After a grammar change or a moved pin alters that list, script/parse-examples rewrites it; review its diff before committing;
• a performance check (test/unit/performance.test.ts) that recovering from an error on each of 10,000 lines takes linear time, since consumers parse files while they are being edited. It loads the Wasm build through @willbooster/web-tree-sitter, which bun run build/ci rebuilds after regenerating the parser;
• checks that the Wasm build parses Kotlin through @willbooster/web-tree-sitter in Chromium (test/unit/browser.test.ts) and in Cloudflare Workers with and without Node.js compatibility (test/unit/workers.test.ts).

CI also runs these tests on Linux arm64 and macOS, where the Rust binding compiles the parser natively, and fuzzes the parser with libFuzzer and sanitizers (.github/workflows/robustness.yml).

References

• Kotlin Grammar