% GHCup
% Julian Ospald
% June 07, 2024

# Introduction

## What is GHCup?

![](what.jpg)

## State of 2019

::: incremental

* stack is the only "Haskell Installer"
* no unified alternative for cabal users
* distro packages, nix, manual installs, ...
* 🤮

:::

## How it started

::: incremental

* 🤹 small team at work (Capital Match), using different platforms
  - originally used stack
  - cabal distro packages constantly out of date
* 🦾 first version was 165 LOC
  - Posix shell
* ![](linux.png){#id .class height=32px} only supported linux and mac
* ![](rust.png){#id .class height=32px} inspired by **rustup**

:::

## GHCup today

[Haskell Survey 2022](https://taylor.fausak.me/2022/11/18/haskell-survey-results/#s2q1):

![](survey.png)

. . .

- over **17k** LOC Haskell
- supports all platforms: Linux, Windows, macOS, FreeBSD

## GHCup and haskell.org

The default installer:

![](downloads.png)

. . .

* provides infrastructure (home page, downloads)

## GHCup and the Haskell Foundation

::: incremental

* affiliation: [https://haskell.foundation/affiliates/](https://haskell.foundation/affiliates/)
* pays for CI
* pays consultants to assist the project

:::

# Philosophy

## What is a good installer?

::: incremental

* it installs (just that)
  - everywhere
* intuitive interface
  - `ghcup install ghc`
* good documentation
  - but you shouldn't have to read it
* get out of the way
  - has no self-fulfilling purpose

:::

## Goals and principles

::: incremental

- ☮️ unification
- unix principles
  - 🛠️ do one thing and do it well
  - ⚗️ pipes, compose stdout and stdin (re-usable)
- 🎁 good re-distribution
- 🛣️ user experience

:::

## What is GHCup (simplified)?

```sh
curl -s -L 'https://downloads.haskell.org/~ghc/9.6.5/ghc-9.6.5-x86_64-fedora33-linux.tar.xz' |
  tar -xJ -C /tmp                              &&
  cd /tmp/ghc-9.6.5-x86_64-unknown-linux/      &&
  ./configure --prefix="$HOME/.local"          &&
  make install                                 &&
  rm -rf /tmp/ghc-9.6.5-x86_64-unknown-linux/
```



## What is GHCup really?

* [https://hasufell.github.io/posts/2023-11-14-ghcup-is-not-an-installer.html](https://hasufell.github.io/posts/2023-11-14-ghcup-is-not-an-installer.html)

::: incremental

* ![](open-box.png){#id .class width=32 height=32px} installer
* ![](debian.png){#id .class width=32 height=32px} distribution channel
* ![](feedback.png){#id .class width=32 height=32px} feedback channel
* ![](qa.png){#id .class width=32 height=32px} testing/QA gateway
* ![](user.png){#id .class width=32 height=32px} provider of sane defaults (e.g. "recommended" GHC version)
* ![](chain-saw.png){#id .class width=32 height=32px} glue for holistic toolchain experience
  - VSCode, stack, cabal-install integration
* ![](ghaction.png){#id .class width=32 height=32px} CI provisioning (e.g. github actions)

:::

# Relationships

## Upstream (dependencies)

- supported tools
    - GHC
    - Cabal
    - HLS
    - Stack

. . .

- decisions that affect us
  - release frequency
  - upstream CI
  - platform support
  - binary distributions (the `.tar.gz`/`.zip`)

## Downstream (dependents)

- ![](haskell_logo.png){#id .class height=32px} Haskell developers
  - beginners, advanced, students, companies
- ![](person.png){#id .class width=32 height=32px} end users (e.g. compiling pandoc from source)
- ![](ghaction.png){#id .class width=32 height=32px} GitHub CI
  - GitHub images, Haskell repos
- 🪞 mirrors
  - [sjtug](https://mirror.sjtu.edu.cn/docs/ghcup)
- 🧰 tools
  - [vscode-haskell](https://github.com/haskell/vscode-haskell), [Haskell playground](https://play.haskell.org/), [nvim-lsp-installer](https://github.com/williamboman/nvim-lsp-installer)

# The installer in detail

## How does it work?

* **Architectural components**
    - ![](sh-file.png){#id .class height=32px} bootstrap scripts
    - ![](exe-file.png){#id .class height=32px} ghcup binary (compiled)
    - ![](config-file.png){#id .class height=32px} ghcup-metadata

. . .

* **Logical components**
    - ![](terminal.png){#id .class height=32px} cli interface
    - ![](file.png){#id .class height=32px} file layout / installation destination
    - ![](tar.png){#id .class height=32px} bindist selection
    - ![](brick-final-clearbg.png){#id .class height=32px} tui interface
    - ![](config.svg){#id .class height=32px} configuration

## Basic CLI (context)

* **Architectural components**
    - [ ] ![](sh-file.png){#id .class height=32px} bootstrap scripts
    - [x] ![](exe-file.png){#id .class height=32px} ghcup binary (compiled)
    - [ ] ![](config-file.png){#id .class height=32px} ghcup-metadata
* **Logical components**
    - [x] ![](terminal.png){#id .class height=32px} cli interface
    - [ ] ![](file.png){#id .class height=32px} file layout / installation destination
    - [ ] ![](tar.png){#id .class height=32px} bindist selection
    - [ ] ![](brick-final-clearbg.png){#id .class height=32px} tui interface
    - [ ] ![](config.svg){#id .class height=32px} configuration

## Basic CLI

::: incremental

* show all available tools / versions
  ```sh
  ghcup list
  ```
* install a tool
  ```sh
  ghcup install ghc latest
  ```
* make a tool version the default
  ```sh
  ghcup set ghc latest
  ```
* remove a tool version
  ```sh
  ghcup rm ghc 9.10.1
  ```

:::

## File layout (context)

* **Architectural components**
    - [ ] ![](sh-file.png){#id .class height=32px} bootstrap scripts
    - [x] ![](exe-file.png){#id .class height=32px} ghcup binary (compiled)
    - [ ] ![](config-file.png){#id .class height=32px} ghcup-metadata
* **Logical components**
    - [ ] ![](terminal.png){#id .class height=32px} cli interface
    - [x] ![](file.png){#id .class height=32px} file layout / installation destination
    - [ ] ![](tar.png){#id .class height=32px} bindist selection
    - [ ] ![](brick-final-clearbg.png){#id .class height=32px} tui interface
    - [ ] ![](config.svg){#id .class height=32px} configuration

## File layout

::: incremental

* root dir
  ```sh
  $ ls ~/.ghcup
  📁bin 📁ghc 📁hls
  📁cache 📁db 📁logs 📁tmp 🗑️trash 📄config.yaml 📄env
  ```

* GHC and HLS are installed into sub-directories
  ```sh
  $ ls ~/.ghcup/ghc
  📁8.10.7 📁9.0.2 📁9.2.8
  ```

* bin directory is mostly symbolic links (compare with [update-alternatives](https://man7.org/linux/man-pages/man1/update-alternatives.1.html))
  ```sh
  $ ls ~/.ghcup/bin
  📄ghcup
  🔗cabal 📄cabal-3.10.3.0
  🔗ghc 🔗ghc-8.10 🔗ghc-8.10.7 🔗ghc-9.0 🔗ghc-9.0.2 🔗ghc-9.2 🔗ghc-9.2.8
  ```
:::

## Bindist selection (context)

* **Architectural components**
    - [ ] ![](sh-file.png){#id .class height=32px} bootstrap scripts
    - [x] ![](exe-file.png){#id .class height=32px} ghcup binary (compiled)
    - [x] ![](config-file.png){#id .class height=32px} ghcup-metadata
* **Logical components**
    - [ ] ![](terminal.png){#id .class height=32px} cli interface
    - [ ] ![](file.png){#id .class height=32px} file layout / installation destination
    - [x] ![](tar.png){#id .class height=32px} bindist selection
    - [ ] ![](brick-final-clearbg.png){#id .class height=32px} tui interface
    - [ ] ![](config.svg){#id .class height=32px} configuration

## Bindist selection (sysinfo)

**Gather system information:**

::: incremental

* module `GHCup.Platform`
* `System.Info.arch` and `System.Info.os` (compile-time strings)
* distro detection mostly via `/etc/os-release`
    - specified by [freedesktop.org](https://www.freedesktop.org/software/systemd/man/latest/os-release.html)
    - using [os-release](https://hackage.haskell.org/package/os-release) package for parsing

:::

## Bindist selection (mapping)

**Map binaries to systems:**

::: incremental

- binary compatibility (platform, distro, distro version)
  - finite set of binaries
  - statically linked GHC?
- static mapping in [ghcup-metadata YAML files](https://github.com/haskell/ghcup-metadata/blob/develop/ghcup-0.0.8.yaml)
  - Tool -> Version -> Architecture -> Platform/Distro -> binary URL
  - mapping based on binary compatibility
    - [https://gitlab.haskell.org/ghc/ghc/-/wikis/platforms/linux](https://gitlab.haskell.org/ghc/ghc/-/wikis/platforms/linux)
- alternative dynamic logic (utilizing `ldconfig -p` output)
  - for stack compatibility
- updated on every release
- "channels"

:::

## Installation flow

![](install-flow.svg){#id .class height=500px}

## TUI interface (context)

* **Architectural components**
    - [ ] ![](sh-file.png){#id .class height=32px} bootstrap scripts
    - [x] ![](exe-file.png){#id .class height=32px} ghcup binary (compiled)
    - [ ] ![](config-file.png){#id .class height=32px} ghcup-metadata
* **Logical components**
    - [ ] ![](terminal.png){#id .class height=32px} cli interface
    - [ ] ![](file.png){#id .class height=32px} file layout / installation destination
    - [ ] ![](tar.png){#id .class height=32px} bindist selection
    - [x] ![](brick-final-clearbg.png){#id .class height=32px} tui interface
    - [ ] ![](config.svg){#id .class height=32px} configuration

## TUI interface

![](matrix.png){#id .class height=550px}

## Configuration (context)

* **Architectural components**
    - [X] ![](sh-file.png){#id .class height=32px} bootstrap scripts
    - [x] ![](exe-file.png){#id .class height=32px} ghcup binary (compiled)
    - [x] ![](config-file.png){#id .class height=32px} ghcup-metadata
* **Logical components**
    - [ ] ![](terminal.png){#id .class height=32px} cli interface
    - [ ] ![](file.png){#id .class height=32px} file layout / installation destination
    - [ ] ![](tar.png){#id .class height=32px} bindist selection
    - [ ] ![](brick-final-clearbg.png){#id .class height=32px} tui interface
    - [x] ![](config.svg){#id .class height=32px} configuration

## Configuration

::: incremental

* Types of configuration:
  - environment variables
  - cli switches / TUI options
  - config file (`~/.ghcup/config.yaml`)
* e.g.
  - env: `GHCUP_INSTALL_BASE_PREFIX` (default `$HOME`)
  - cli: `ghcup install ghc -u <url> <version>`
  - config: `url-source` (selecting and mixing "channels")
    - file/http/https URI
    - `GHCupURL`
    - `StackSetupURL`

:::

## Phew

![](headache.png){#id .class height=550px}

# Distribution

## What is distribution?

* QA gate between "upstream" and "downstream"
* trust relationship (with upstream and downstream)
* release selection and defaults
* binary distribution

## What happens on e.g. a GHC release

- testing and inspection of bindists
  - manual
  - automated at [github.com/haskell/ghcup-metadata](https://github.com/haskell/ghcup-metadata/blob/develop/.github/workflows/bindists.yaml)
- fixing bindists
- building additional bindists (e.g. FreeBSD)

. . .

- forks at [github.com/stable-haskell](https://github.com/stable-haskell)
  - builds cabal, stack and HLS binaries
  - GHC TBD

## The "recommended" versions (defaults)

* community adoption (both industry and "open source")
* stack LTS
* HLS support
* known issues and regressions
* GHC HQs opinion and support window
* must be consistent across platforms

# Contributing

## How to contribute

::: incremental

- loose project structure (BDFL)
- discuss early
- repositories
   - [github.com/haskell/ghcup-hs](https://github.com/haskell/ghcup-hs): documentation, bootstrap-scripts, ghcup exe
   - [github.com/haskell/ghcup-metadata](https://github.com/haskell/ghcup-metadata): bindist mapping (YAML), bindist testing
- build with cabal/stack
- communication
  - [#haskell-ghcup](https://kiwiirc.com/nextclient/irc.libera.chat/?nick=Guest%7C?##haskell-ghcup) on libera IRC
  - [#ghcup:matrix.org](https://matrix.to/#/#ghcup:matrix.org) (bridged with IRC)
  - [github issues](https://github.com/haskell/ghcup-hs/issues)
  - [haskell discourse](https://discourse.haskell.org/) (interacting with the community)

:::

## Getting started

Head over to [https://github.com/haskell/ghcup-hs/issues/1074](https://github.com/haskell/ghcup-hs/issues/1074) (`zurihac` labeled issue).

## Advanced topics

- bootstrap scripts
- windows and MSYS2
- security
- HLS/GHC interaction
- reproducibility
- stack integration
- bindist work (curation)
- isolated installs
- mirrors