Build System Overview
ReScript comes with a build system, bsb, that's meant to be fast, lean and used as the authoritative build system of the community.
Bsb provides a few templates to quickly start a new project:
bsb -init my-directory-name
Feel free to inspect the various files in the newly generated directory. To see all the templates available, do:
The build description file is called
bsconfig.json. Every ReScript project needs one.
To build a project, run:
-w to keep the built-in watcher running. Any new file change will be picked up and the build will re-run.
Note: third-party libraries (in
node_modules) aren't watched, as doing so may exceed the node.js watcher count limit. If you're doing quick and dirty modifications inside
node_modules, you have to do
bsb -clean-world -make-world to rebuild them.
Note 3: If you are developing across multiple devices, you may find the
-ws configuration useful in order to have live-reloading across the network. Possible configurations are:
bsb -make-world -w -ws _(default)
bsb -make-world -w -ws 0.0.0.0:9999
bsb -make-world -w -ws 5000
To build only yourself, use
bsb -help to see all the available options.
If you ever get into a stable build for edge-case reasons, use:
bsb -clean to clean only your own artifacts.
Bsb generates a
.merlin file, used by various editor plugins under the hood to power e.g. autocomplete, type hint, diagnosis, etc.
A typical problem with traditional build systems is that they're not resilient against the user moving/deleting source files. Most don't clean up the old artifacts correctly after such user action*. Bsb is unfortunately no different, unless you turn on
"suffix": ".bs.js" in
bsconfig.json, in which case we can track which JS artifact belongs to which source file correctly, even against source file moving/deletion.
* One such build system that tracks these correctly & efficiently is Tup. See the (rather accessible!) paper here. Unfortunately, Tup's implementation uses FUSE and other systems, which we can't safely use on every platform.