@willbooster/tree-sitter-python

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

This fork builds on upstream v0.25.0 with grammar, scanner, and highlighting fixes, including Python 3.15 unpacking comprehensions. It ships a compact parser generated by the parser generator of WillBooster/tree-sitter. The parser carries that fork's own ABI number, so it loads only with the WillBooster runtime (willbooster-tree-sitter or @willbooster/web-tree-sitter) 2.0.0 or later, not with upstream's tree-sitter.

Usage

The npm package ships tree-sitter-python.wasm for @willbooster/web-tree-sitter, which runs in Node.js, Bun, browsers, and Cloudflare Workers. The parser requires runtime 2.0.0 or later.

In Node.js and Bun, load the grammar from its path:

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-python/tree-sitter-python.wasm'));
parser.setLanguage(await Language.load(wasmPath));
const tree = parser.parse('def main():\n    pass\n');

In browsers, load the grammar from its URL. With Vite:

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

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

In Cloudflare Workers, which do not allow compiling Wasm at run time, import both .wasm files as modules:

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

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

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

In Rust, depend on the crate and on willbooster-tree-sitter, the runtime this package is tested and fuzzed with. The parser requires runtime 2.0.0 or later:

[dependencies]
tree-sitter = { package = "willbooster-tree-sitter", version = "2" }
tree-sitter-python = { package = "willbooster-tree-sitter-python", version = "2" }

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

Development

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

The scripts and tests generate, build, test, and parse with script/tree-sitter, the tree-sitter CLI of the WillBooster/tree-sitter runtime version locked in Cargo.lock, since the generator and the runtime of upstream's CLI are not the ones this package ships with. Its first run downloads that CLI from the runtime's GitHub Release, or builds it with cargo (whose build runs the CMake that mise.toml pins) when the download fails or the release has no binary that runs here. Run other CLI commands through it as well (e.g. script/tree-sitter parse file.py).

bun run generate records a fresh generation profile from the applicable test/corpus cases and Git-tracked Python files in examples/, then generates compact parser tables. The parser also embeds metadata from tree-sitter.json. After changing a grammar, tree-sitter.json, a corpus case, or a tracked example, regenerate and commit src/. Stage added or removed examples with git add -A examples before generation so the profile uses the intended file list. Profiles in .tmp/generation-profiles/ are temporary and must not be committed. bun run build-wasm, bun run build/ci, and the release build regenerate the parsers before compiling them.

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): script/fuzz-corpus runs tree-sitter fuzz, which 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 the real-world Python files in examples/, the checked-in ones and those of the cloned repositories, fail to parse exactly as listed in script/known-failures.txt. The first run clones the repositories. 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 line takes linear time (ten times the lines take about ten times the CPU time, under a ceiling), 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;
• a native CLI crash regression for deeply indented strings (test/unit/deepIndentation.test.ts);
• a check that package.json and Cargo.lock test the same runtime version (test/unit/runtimeVersion.test.ts);
• checks that the Wasm build parses in Chromium (test/unit/browser/) and in Cloudflare Workers with and without Node.js compatibility (test/unit/workerd.test.ts). Run bun run test/ci-setup once to install Chromium.

Tests and script/parse-examples keep native parser builds under this checkout's .tmp/ instead of the CLI cache shared by every checkout. See test/unit/run.ts, test/unit/deepIndentation.test.ts, script/fuzz-corpus, and script/parse-examples for their build locations and cleanup.

CI also runs these tests on Linux arm64 and macOS, where the CLI compiles the parser and the scanner with the platform's C compiler as the crate does for its users, and fuzzes the parser with libFuzzer and sanitizers (.github/workflows/robustness.yml).

References

• Python 2 Grammar
• Python 3 Grammar