# Contributing to `package-sets`

This document is meant to be a general guide and FAQ for contributors to this repo.

It defines some policies that are applied, and details how to add new packages and the criteria packages should match to stay in the set.


- [General](#general)
- [Releases](#releases)
- [Will any package be dropped at any point?](#will-any-package-be-dropped-at-any-point)
- [Package-sets maintenance](#package-sets-maintenance)
- [How to add a package to the set](#how-to-add-a-package-to-the-set)
  - [0. Background knowledge](#0-background-knowledge)
    - [Why/how Dhall?](#whyhow-dhall)
    - [Brief detour of how the package-set is structured](#brief-detour-of-how-the-package-set-is-structured)
    - [Prerequisites](#prerequisites)
  - [1. Adding a new package](#1-adding-a-new-package)
  - [2. Verifying a package](#2-verifying-a-package)


## General

All changes go through pull requests.

All packages that are included here must first be published via `bower` with no exceptions. Since there are two distribution methods for packages (the Bower registry and the package sets), we rely on the Bower registry to act as a "central registry of package names" for both methods. This prevents divergence in the ecosystem - e.g. having two different codebases for a package called "prelude".

Packages must comply with the following criteria. The `pulp` commands listed below are used because they handle most of the work for you:
- `bower i -p` must run successfully.  
  This command installs your dependencies and excludes any 'devDependencies'.
- _You must use `pulp version` to version your package._  
  This guarantees that the tag will start with the `v` prefix.
- _You must use `pulp publish` to publish your package._  
  This command will handle all of the publishing work for you. 

## Releases

A "release" of the package set consists in a *git tag* (i.e. what GitHub calls a release).

Releases happen quite often (look at the [release history][releases]), and anyone can request a new release at any time, by just [opening an issue][issues].  
This implies that the `master` branch should always be "release ready".

Releases have the following naming convention:
```
psc-${compiler-version}-${date}
```

Where:
- `compiler-version` is the version of the compiler supported by the package-set.
  Support for different versions of the compiler is implied by SemVer, e.g. if a package-set is compatible with `0.12.2`, then it will be compatible with `0.12.3`, but not `0.12.1` or `0.13.0`.
- `date` is the release date, in `yyyyMMdd` format.

## Will any package be dropped at any point?

For package-sets to be able to keep up with the new releases in the ecosystem, package maintainers should strive for having their packages work with the latest versions of dependencies.

This is because if packages `X@v1` and `Y@v1` depend on package `Z@v1` then if package X releases `v2` that depends on `Z@v2`, then also package Y should be updated to depend on it. (this is because a package-set contains only *one* version of every package)

However, things happen and packages go unmaintained, so there's the need to drop packages from the package-set every once in a while, in order to allow for the majority of the packages to keep up with the latest versions.

Since package-set releases are tied to compiler releases, new compiler releases (happening every 6 weeks) will coincide with outdated packages being dropped from the set.

## Package-sets maintenance

Once one displays sustained interest in the project, they can ask to help maintaining it.  
You can do so by [opening an issue][issues]

## How to add a package to the set

The following section will detail how to add a package to the package-set.

The *TL;DR* about it is:
- add the Dhall package definition in some `src/groups/${username}.dhall` (where `username` is the one of the author of the package)
- run `make setup` and `psc-package verify ${your-new-package-name}`

### 0. Background knowledge

#### Why/how Dhall?

[Dhall](https://github.com/dhall-lang/dhall-lang) is a programming language that guarantees
termination. Its most useful characteristics for uses in this project are:
* Static typing with correct inference: unlike the `packages.json` file, we have the compiler check that we correctly define packages
* Functions: we can use functions to create simple functions for defining packages
* Local and remote path importing: we can use this to mix and match local and remote sources as necessary to build package sets
* Typed records with directed merging: we can use this to split definitions into multiple groupings and apply patching of existing packages as needed

Let's look at the individual parts for how this helps us make a package-set.

#### Brief detour of how the package-set is structured

The files in this package-set are structured as such:

```
-- Package type definition
src/Package.dhall

-- function to define packages
src/mkPackage.dhall

-- packages to be included when building package set
src/packages.dhall

-- package "groups" where packages are defined in records
src/groups/[...].dhall
```

The `Package.dhall` contains the simple type that is the definition of a package:

```hs
{ dependencies : List Text, repo : Text, version : Text }
```

So a given package is nothing more than:
- a list of dependencies
- the git url for the repository
- and the tag or branch that it can be pulled from.

The `mkPackage.dhall` contains a function for creating `Package` values easily:

```hs
   \(dependencies : List Text)
-> \(repo : Text)
-> \(version : Text)
->    { dependencies = dependencies, repo = repo, version = version }
   : ./Package.dhall
```

The `packages.dhall` is the actual "package-set": a record from package names to package definitions.  
It is defined by taking package definitions from the groups and joining them with a right-sided merge.  
This is the file used to generate the `packages.json`.


```hs
   ./groups/purescript.dhall
// ./groups/purescript-contrib.dhall
// ./groups/purescript-web.dhall
// ./groups/purescript-node.dhall
// ...
// ./groups/justinwoo.dhall
```

#### Prerequisites

In order to hack on this project, you should have installed:
- [dhall][dhall]
- [psc-package][psc-package]
- [jq][jq]

### 1. Adding a new package

To add a new package to the package set, you should create a package definition with `mkPackage`, and put it in the group file corresponding to the author's username.

For example, if I wish to add to the package-set the version `v4.2.0` of the package `unicorns` from `someauthor`, I will create the file `src/groups/someauthor.dhall`.

Its content would look something like this:

```hs
    let mkPackage = ./../mkPackage.dhall

in  { unicorns =
        mkPackage
        [ "prelude"
        , "console"
        , "simple-json"
        ]
        "https://github.com/someauthor/purescript-unicorns.git"
        "v4.2.0"
    }
```


### 2. Verifying a package

After adding your package to the Dhall files, you should check that the package-set is still consistent.

In order to verify the addition (or change), you should follow these steps:
- `make setup`: this will setup a test project based on the new package-set
- `psc-package verify ${your-new-package-name}`

Once it verifies correctly, you should check in both the Dhall files and the `packages.json`

You're now ready to commit! 🙂

[jq]: https://github.com/stedolan/jq
[psc-package]: https://github.com/purescript/psc-package/
[dhall]: https://github.com/dhall-lang/dhall-haskell
[releases]: https://github.com/purescript/package-sets/releases
[issues]: https://github.com/purescript/package-sets/issues
[local-setup]: https://github.com/spacchetti/spago#i-still-want-to-use-psc-package-can-this-help-me-in-some-way
[spago]: https://github.com/spacchetti/spago
[bower]: https://bower.io/
[pulp]: https://github.com/purescript-contrib/pulp