@willbooster/tree-sitter-c

C grammar for tree-sitter, forked from tree-sitter/tree-sitter-c. 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 ISO C standard (C23 working draft N3220).

Usage

The npm package ships tree-sitter-c.wasm for @willbooster/web-tree-sitter version 1.2.2 or later, which runs in Node.js, Bun, browsers, and Cloudflare Workers. 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-c/tree-sitter-c.wasm'));
parser.setLanguage(await Language.load(wasmPath));
const tree = parser.parse('int main(void) { return 0; }\n');

In browsers, serve both .wasm files and load them by URL (the example uses Vite's ?url imports):

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

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

Cloudflare Workers do not allow compiling Wasm at run time, so 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 c from '@willbooster/tree-sitter-c/tree-sitter-c.wasm';

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

The package also ships grammar.js, the scanner sources src/scanner.c, src/pragma.h and src/identifier.h, the queries in queries/, and the node types in src/node-types.json for grammars extending C (such as C++). Derived grammars must handle every inherited external token in their scanner, including _preproc_function_name. Port both the _preproc_function_name dispatch and the _preproc_lparen splice-skipping loop from src/scanner.c, using scan_function_macro_name from src/pragma.h. The macro-name token ends before the splices used to determine adjacency, so the parameter scanner must skip them again to reach (.

In Rust, depend on the crate and on willbooster-tree-sitter, the runtime this package is tested and fuzzed with. Restricted switch-body statement queries require this fork’s generator and runtime together:

[dependencies]
tree-sitter = { package = "willbooster-tree-sitter", version = "1.2.2" }
tree-sitter-c = { package = "willbooster-tree-sitter-c", version = "3" }

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

Development

mise install
bun install --frozen-lockfile
bun run test/ci-setup # installs Chromium for the browser test
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.c).

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 in examples/, the checked-in ones and those of the cloned repositories, fail to parse exactly as listed in script/known-failures.txt. Many of the listed files use preprocessor conditionals or macros that tree-sitter parses without expanding them. 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, 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 (test/unit/runtimeVersion.test.ts) that @willbooster/web-tree-sitter in package.json and willbooster-tree-sitter in Cargo.lock are the same version, since the Wasm tests run on the former and the Rust tests, the fuzzer, and the CLI on the latter;
• tests that load the Wasm build with @willbooster/web-tree-sitter in Chromium (test/e2e/browser.test.ts) and in Cloudflare Workers with and without Node.js compatibility (test/e2e/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 parser of its own in .tmp/fuzz for each run and deletes it afterwards.

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

• The grammar was originally adapted from this C99 grammar.
• C23 working draft N3220 and C11 working draft N1570.