Hacktoberfest 2026: the issues maintainers tagged for October, open and beginner-friendly. Browse Hacktoberfest issues

Publish the parser as a standalone OCaml library

Open
  • Is something wrong?
#8,727 0 comments 0 reactions 0 assignees View on GitHub

Maintainers usually reply within 1 day

Nobody has claimed this yet.

Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
35/100
Issue type
Feature
Clarity
Clearly specified
Activity status
Active
Tech stack
ocaml
Domain
build-system

Research direction

Start by reading the dune graph and the listed blocker issues #8567 and #8624, then trace the parser’s dependency closure with ocamldep. The proposed work spans AST boundaries, dependencies, namespacing, global state, C stubs, packaging, and CI, so it is not a small standalone change. Done means a clean-switch dune build -p rescript-syntax succeeds with only ocaml and dune dependencies.

Written by the indexing model from the issue text.

Description

Goal

Publish the ReScript parser/printer as a reusable OCaml library that needs only ocaml and dune.

Current state

The dune graph is syntax → ml → {ext, flow_parser}. flow_parser is the only part with heavy OPAM dependencies (ppxlib, ppx_deriving, ppx_gen_rec, wtf8, plus a vendored sedlex ppx). The parser pulls all of them in.

Transitive module closure of Res_core / Res_printer / Res_driver (via ocamldep):

library modules reached
syntax/src 16 / 24
ml ~18 / 91
ext 20 / 66
flow_parser 27 / 27

The parser needs only a small part of ml/ext. A few edges drag in the rest.

Blockers

  1. The AST layer depends on the Flow JS parser.
    • ml/ast_payload.ml calls Parser_flow and Classify_function to classify %raw payloads.
    • ml/ast_helper.ml uses Ast_payload, so the plain AST builder depends on flow_parser.
    • Related: #8567 (replacing/vendoring the Flow parser). This issue needs Flow out of the parser's dependency closure either way.
  2. Compiler semantics live in Parsetree. Prim_ffi of {spec: External_ffi_types.t} and Prim_inline_const tie the syntax tree to FFI/codegen types. Tracked in #8624 (section C / step B).
  3. No library boundary. syntax depends on all of ml (the type checker).
  4. No namespacing. All libraries are (wrapped false). Module names clash with compiler-libs / ppxlib (Location, Misc, Warnings, Ident, Parsetree, Asttypes, Longident, Ast_helper, Printast, Pprintast) and are generic (Literals, Map_gen, Identifiable).
  5. Global mutable state. Location → Clflags / Warnings / Misc. Diagnostics go through global refs, stderr and exceptions.
  6. C stubs and build profiles. ext has C stubs reachable from the parser (Ext_platform_primitives). Native vs. playground behavior is chosen with the browser profile and copy rules instead of select or virtual libraries.

Proposed plan

  • Split Ast_payload into a pure payload-inspection part and a %raw/%re classification part. Move the classification to frontend/core, and make Ast_helper flow-free. This alone drops ppxlib/ppx_deriving/ppx_gen_rec/wtf8 from the parser.
  • Move Prim_ffi / Prim_inline_const out of the parsetree (see #8624).
  • Extract a small rescript_ast library (Parsetree, Asttypes, Longident, Location, Ast_helper, pure Ast_payload, needed ext helpers). Make syntax depend on it instead of ml. Decide where jsx_ppx and Res_outcome_printer (Outcometree) go.
  • Make the AST library free of C stubs, or give it a pure-OCaml fallback, so it works under js_of_ocaml without a custom profile.
  • Wrap the published libraries ((wrapped true) or (wrapped (transition …))).
  • Expose a parser API that returns diagnostics and takes explicit config instead of relying on global state.
  • Add an opam package (e.g. rescript-syntax) with public_names. Its only dependencies should be ocaml and dune.
  • Align with #8624 (parsetree v1) for API/AST stability.
  • Confirm licensing for the package: compiler-derived files are LGPL with the OCaml linking exception.
  • Add a CI job that builds the package alone in a clean switch (dune build -p rescript-syntax) to catch dependency regressions.
Dominant language
ReScript
Stars
7.5k
Forks
483
Avg merge
1d 1h
Merged PRs (30d)
120

Getting set up

Open in Codespaces

Starts the project's dev container in your browser, under your own GitHub account.

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from rescript-lang/rescript

All issues in rescript-lang/rescript

Similar issues

More Build System issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.