Rewatch

Info

Rewatch is an alternative build system for the Rescript Compiler (which uses a combination of Ninja, OCaml and a Node.js script). It strives to deliver consistent and faster builds in monorepo setups. Bsb doesn't support a watch-mode in a monorepo setup, and when setting up a watcher that runs a global incremental compile it's consistent but very inefficient and thus slow.

We couldn't find a way to improve this without re-architecting the whole build system. The benefit of having a specialized build system is that it's possible to completely tailor it to ReScript and not being dependent of the constraints of a generic build system like Ninja. This allowed us to have significant performance improvements even in non-monorepo setups (30% to 3x improvements reported).

Project Status

This project should be considered in beta status. We run it in production at Walnut. We're open to PR's and other contributions to make it 100% stable in the ReScript toolchain.

Usage

Install the package

yarn add @rolandpeelen/rewatch

Build / Clean / Watch

yarn rewatch build

yarn rewatch clean

yarn rewatch watch

You can pass in the folder as the second argument where the 'root' bsconfig.json lives. If you encounter a 'stale build error', either directly, or after a while, a clean may be needed to clean up some old compiler assets.

Full Options

Find this output by running yarn rewatch --help.

Rewatch is an alternative build system for the Rescript Compiler bsb (which uses Ninja internally). It strives to deliver consistent and faster builds in monorepo setups with multiple packages, where the default build system fails to pick up changed interfaces across multiple packages

Usage: rewatch [OPTIONS] [COMMAND] [FOLDER]

Arguments:
  [COMMAND]
          Possible values:
          - build: Build using Rewatch
          - watch: Build, then start a watcher
          - clean: Clean the build artifacts

  [FOLDER]
          The relative path to where the main bsconfig.json resides. IE - the root of your project

Options:
  -f, --filter <FILTER>
          Filter allows for a regex to be supplied which will filter the files to be compiled. For instance, to filter out test files for compilation while doing feature work

  -a, --after-build <AFTER_BUILD>
          This allows one to pass an additional command to the watcher, which allows it to run when finished. For instance, to play a sound when done compiling, or to run a test suite. NOTE - You may need to add '--color=always' to your subcommand in case you want to output colour as well

  -n, --no-timing <NO_TIMING>
          [possible values: true, false]

  -c, --create-sourcedirs <CREATE_SOURCEDIRS>
          This creates a source_dirs.json file at the root of the monorepo, which is needed when you want to use Reanalyze
          
          [possible values: true, false]

      --compiler-args <COMPILER_ARGS>
          This prints the compiler arguments. It expects the path to a rescript.json file. This also requires --bsc-path and --rescript-version to be present

      --rescript-version <RESCRIPT_VERSION>
          To be used in conjunction with compiler_args

      --bsc-path <BSC_PATH>
          A custom path to bsc

  -h, --help
          Print help (see a summary with '-h')

  -V, --version
          Print version

Contributing

Pre-requisites:

Rust
NodeJS - For running testscripts only
Yarn or Npm - Npm probably comes with your node installation

cd testrepo && yarn (install dependencies for submodule)
cargo run

Running tests: