Docs / Language Manual / Pinned Dependencies

Pinned Dependencies

Usually we'd recommend to use ReScript in a single-codebase style by using one rescript.json file for your whole codebase.

There are scenarios where you still want to connect and build multiple independent ReScript packages for one main project though (npm workspaces-like "monorepos"). This is where pinned-dependencies come into play.

Package Types

Before we go into detail, let's first explain all the different package types recognized by the build system:

  • Toplevel (this is usually the final app you are building, which has dependencies to other packages)

  • Pinned dependencies (these are your local packages that should always rebuild when you build your toplevel, those should be listed in bs-dependencies and pinned-dependencies)

  • Normal dependencies (these are packages that are consumed from npm and listed via bs-dependencies)

Whenever a package is being built (rescript build), the build system will build the toplevel package with its pinned-dependencies. So any changes made in a pinned dependency will automatically be reflected in the final app.

Build System Package Rules

The build system respects the following rules for each package type:


  • Warnings reported

  • Warn-error respected

  • Builds dev dependencies

  • Builds pinned dependencies

  • Runs custom rules

  • Package-specs like ES6/CommonJS overrides all its dependencies

Pinned dependencies

  • Warnings reported

  • Warn-error respected

  • Ignores pinned dependencies

  • Builds dev dependencies

  • Runs custom rules

Normal dependencies

  • Warnings, warn-error ignored

  • Ignores dev directories

  • Ignores pinned dependencies

  • Ignores custom generator rules

So with that knowledge in mind, let's dive into some more concrete examples to see our pinned dependencies in action.


Yarn workspaces

Let's assume we have a codebase like this:

myproject/ app/ - src/App.res - rescript.json common/ - src/Header.res - rescript.json myplugin/ - src/MyPlugin.res - rescript.json package.json

Our package.json file within our codebase root would look like this:

{ "name": "myproject", "private": true, "workspaces": { "packages": [ "app", "common", "myplugin" ] } }

Our app folder would be our toplevel package, consuming our common and myplugin packages as pinned-dependencies. The configuration for app/rescript.json looks like this:

{ "name": "app", "version": "1.0.0", "sources": { "dir" : "src", "subdirs" : true }, /* ... */ "bs-dependencies": [ "common", "myplugin" ], "pinned-dependencies": ["common", "myplugin"], /* ... */ }

Now, whenever we are running rescript build within our app package, the compiler would always rebuild any changes within its pinned dependencies as well.

Important: ReScript will not rebuild any pinned-dependencies in watch mode! This is due to the complexity of file watching, so you'd need to set up your own file-watcher process that runs rescript build on specific file changes.