@willbooster/tree-sitter-c-sharp

C# grammar for tree-sitter, forked from tree-sitter/tree-sitter-c-sharp. 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 C# language specification.

The grammar is based upon the Roslyn grammar with changes in order to:

• Deal with differences between the parsing technologies
• Work around some bugs in that grammar
• Handle #if, #else, #elif, #endif blocks
• Support syntax highlighting/parsing of fragments
• Simplify the output tree
• Reduce parser state count and complexity
• Be in-line with tree-sitter's convention where applicable

Known gaps:

• var and await cannot be used as identifiers everywhere they are valid

Usage

The npm package ships tree-sitter-c_sharp.wasm for @willbooster/web-tree-sitter, which runs in Node.js, Bun, browsers, and Cloudflare Workers. Use runtime version 1.1.2 or later: browser loading requires its asynchronous instantiation support for this grammar. Install the runtime alongside the grammar when using the Wasm parser; it remains an optional peer for consumers that only use the grammar source or queries.

In Node.js and Bun, load it from the package:

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-c-sharp/tree-sitter-c_sharp.wasm'));
parser.setLanguage(await Language.load(wasmPath));
const tree = parser.parse('class Program {}\n');

In browsers, serve both .wasm files and load them 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 cSharpUrl from '@willbooster/tree-sitter-c-sharp/tree-sitter-c_sharp.wasm?url';

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

In Cloudflare Workers, which do not allow compiling Wasm at run time, import both .wasm files as modules (Wrangler compiles them at build time) and pass them to Parser.init and Language.load. This works with and without the nodejs_compat flag:

import { Language, Parser } from '@willbooster/web-tree-sitter';
import runtime from '@willbooster/web-tree-sitter/web-tree-sitter.wasm';
import cSharp from '@willbooster/tree-sitter-c-sharp/tree-sitter-c_sharp.wasm';

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

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, whose fixes keep incremental reparses consistent with fresh parses (the grammar also loads in the upstream tree-sitter crate 0.27, whose error recovery never ends on some malformed input):

[dependencies]
tree-sitter = { package = "willbooster-tree-sitter", version = "1.1.2" }
tree-sitter-c-sharp = { package = "willbooster-tree-sitter-c-sharp", version = "2" }

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

Development

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

script/tree-sitter (also bun run tree-sitter) runs the tree-sitter CLI of WillBooster/tree-sitter at the runtime version locked in Cargo.lock, so the parser is generated, built, tested, and fuzzed with the generator and the runtime this package ships. The first run downloads that CLI from its GitHub Release into .tmp/, or builds it with cargo (with the cmake that mise.toml pins) when the download fails or the release has no binary that runs here. The tree-sitter-cli package provides only the types of the grammar DSL that grammar.js checks against; its tree-sitter binary is upstream's.

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 C# 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 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 check that package.json and Cargo.lock test the same runtime version (test/unit/runtimeVersion.test.ts);
• checks that the Wasm build parses C# with @willbooster/web-tree-sitter in Chromium (test/unit/browser.test.ts, which needs Chromium installed once by bunx playwright install chromium) and in Cloudflare Workers with and without nodejs_compat (test/unit/workers.test.ts).

The tests and script/parse-examples compile the parser into .tmp/tree-sitter-lib rather than the CLI's cache shared by every checkout; script/fuzz-corpus builds a per-run parser in .tmp/fuzz and deletes it afterwards. mise.toml sets TREE_SITTER_LIBDIR to .tmp/tree-sitter-lib as well, so other tree-sitter commands run in the checkout use this checkout's parser too.

cargo test also replays edits that tree-sitter fuzz found to break incremental parsing on runtimes without the fixes of willbooster-tree-sitter.

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 on the willbooster-tree-sitter runtime locked in Cargo.lock (.github/workflows/robustness.yml).

References

• C# language specification
• Official C# 8 Draft Language Spec provides chapters that formally define the language grammar.
• Roslyn C# language grammar export
• SharpLab (web-based syntax tree playground based on Roslyn)