rescript-lezer

This is a ReScript grammar for the lezer parser system.

The top option can be set to "SingleExpression" to parse an expression instead of a full program.

Grammar Audit

Use the audit script to find remaining grammar bugs against the official ReScript parser.

The compiler and corpus are pinned in the vendored/rescript Git submodule. Initialize it once, then build the parser comparator with ReScript's OCaml/dune dependencies installed (see its CONTRIBUTING.md):

git submodule update --init vendored/rescript
cd vendored/rescript
dune build compiler/bsc/rescript_compiler_main.exe
cd ../..

Quick run

npm run build
npm run audit:grammar

Corpus regression check

npm run test:corpus

This checks the syntax fixtures, runtime packages, and scripts in the pinned checkout. It also compares fresh and incremental trees across 1,000 reproducible edits. It fails on compiler-valid parse errors, incremental mismatches, or crashes. Compiler-rejected fixtures remain visible in the full differential audit.

GitHub Actions runs npm test and this corpus check on pushes and pull requests, and saves the JSON audit report as the grammar-audit artifact.

Strict agreement

npm run audit:grammar:strict

Custom run

node scripts/audit-grammar.mjs \
  --mode all \
  --max-files 10000 \
  --fuzz-cases 500 \
  --incremental-cases 300 \
  --include-idempotency \
  --report /tmp/rescript-lezer-audit.json

What it checks

• Differential parse agreement vs ReScript (-only-parse) on upstream corpus files
• Mutation fuzzing with mismatch detection
• Incremental parse consistency (incremental tree vs fresh parse)

--corpus adds directories to the default corpus. Reports include error positions and the full source and edit for reproducing fuzz and incremental failures. Use a fixed --seed to reproduce edits, and --rescript-root or RESCRIPT_ROOT to compare against another compiler checkout.

Publishing

Version tags (v0.9.1, for example) trigger .github/workflows/publish.yml. The workflow runs the full test suite and corpus check, verifies that the tag matches package.json, then builds and publishes to npm. Only stable versions are supported.

Before the first automated release, push the workflow and configure a Trusted Publisher in the npm settings for @tsnobip/rescript-lezer:

• GitHub user: tsnobip
• Repository: rescript-lezer
• Workflow filename: publish.yml
• Allow direct publishing with npm publish

Publishing uses OIDC, so no npm token secret is needed. To release from a clean checkout of the release branch:

npm version patch # or minor / major
git push origin HEAD --follow-tags

npm version updates the package and lockfile, commits the change, and creates the version tag. Failed workflow runs can be rerun from GitHub Actions.

The code is licensed under an MIT license.