Build System Overview

ReScript comes with a build system, rescript, that's fast, lean and used as the authoritative build system of the community.

Every ReScript project needs a build description file, rescript.json.

Options

See rescript help:

❯ rescript help
Usage: rescript <options> <subcommand>

`rescript` is equivalent to `rescript build`

Options:
  -v, -version  display version number
  -h, -help     display help

Subcommands:
  build
  clean
  format
  convert
  dump
  help

Run `rescript <subcommand> -h` for subcommand help. Examples:
  rescript build -h
  rescript format -h

Build Project

Each build will create build artifacts from your project's source files.

To build a project (including its dependencies / pinned-dependencies), run:

SH
rescript

Which is an alias for rescript build.

To keep a build watcher, run:

SH
rescript -w

Any new file change will be picked up and the build will re-run.

Note: third-party libraries (in node_modules, or via pinned-dependencies) aren't watched, as doing so may exceed the node.js watcher count limit.

Note 2: In case you want to set up a project in a JS-monorepo-esque approach (npm and yarn workspaces) where changes in your sub packages should be noticed by the build, you will need to define pinned dependencies in your main project's rescript.json. More details here.

Clean Project

If you ever get into a stale build for edge-case reasons, use:

SH
rescript clean

Compile with stricter errors in CI

Since 11.1

You may want to compile your project with stricter rules for production, than when developing. With the -warn-error build flag, this can easily be done, for instance in a continuous integration script. E.g.:

SH
rescript -warn-error +110

Here, warning number 110, which is triggered when a %todo has been found, gets promoted to an error. The full list of warning numbers can be found here.