Co-authored-by: tomjaguarpaw <tom-github.com@jaguarpaw.co.uk>

2023-01-05 07:32:51 +08:00

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About

All you wanted to know about GHCup.

Team

Author and Maintainer

Julian Ospald (aka: maerwald, hasufell)

Collaborators

Contributors

amesgen
Chris Smith
Anton-Latukha
Brian McKenna
Huw campbell
Tom Ellis
Sigmund Vestergaard
Ron Toland
Paolo Martini
Mario Lang
Jan Hrček
vglfr
Fendor
Enrico Maria De Angelis
Emily Pillmore
Colin Barrett
Artur Gajowy

How to help

if you want to contribute code or documentation, check out the issue tracker and the Development guide
if you want to propose features or write user feedback, feel free to open a ticket
if you want to donate to the project, visit our opencollective page

Design goals

simplicity
non-interactive CLI interface
portable
do one thing and do it well (UNIX philosophy)

Non-goals

invoking sudo, apt-get or any package manager
handling system packages
handling cabal projects
being a stack alternative

Distribution policies

Like most Linux distros and other distribution channels, GHCup also follows certain policies. These are as follows:

The end-user experience is our primary concern
- ghcup in CI systems as a use case is a first class citizen
We strive to collaborate with all maintainers of all the tools we support and maintain a good relationship
We may fix build system or other distribution bugs in upstream bindists
- these are always communicated upstream
We may even patch source code of supported tools in very rare cases if that is required to ensure that the end-user experience does not break
- we'll first try to upstream any such required patch and request a new release to avoid downstream patching
- patches will be communicated to the maintainers either way and we'll strive to get their review
- they will also be communicated to the end-user
- they will be uploaded along with the bindist
- we will avoid maintaining long-running downstream patches (currently zero)
We may add bindists for platforms that upstream does not support
- this is currently the case for GHC for e.g. Alpine and possibly FreeBSD in the future
- this is currently also the case for stack on darwin M1
- we don't guarantee for unofficial bindists that the test suite passes at the moment (this may change in the future)
We GPG sign all the GHCup metadata as well as the unofficial bindists
- any trust issues relating to missing checksums or GPG signatures is a bug and given high priority

How

Installs a specified GHC version into ~/.ghcup/ghc/<ver>, and places ghc-<ver> symlinks in ~/.ghcup/bin/.

Optionally, an unversioned ghc link can point to a default version of your choice.

This uses precompiled GHC binaries that have been compiled on fedora/debian by upstream GHC.

Alternatively, you can also tell it to compile from source (note that this might fail due to missing requirements).

cabal-install/HLS/stack are installed in ~/.ghcup/bin/<tool>-<ver> and have unversioned symlinks to the latest version by default (~/.ghcup/bin/<tool>-<ver>).

Known users

Known problems

Custom ghc version names

When installing ghc bindists with custom version names as outlined in installing custom bindists, then cabal might be unable to find the correct ghc-pkg (also see #73) if you use cabal build --with-compiler=ghc-foo. Instead, point it to the full path, such as: cabal build --with-compiler=$HOME/.ghcup/ghc/<version-name>/bin/ghc or set that GHC version as the current one via: ghcup set ghc <version-name>.

This problem doesn't exist for regularly installed GHC versions.

Limited distributions supported

Currently only GNU/Linux distributions compatible with the upstream GHC binaries are supported.

Precompiled binaries

Since this uses precompiled binaries you may run into several problems.

Missing libtinfo (ncurses)

You may run into problems with ncurses and missing libtinfo, in case your distribution doesn't use the legacy way of building ncurses and has no compatibility symlinks in place.

Ask your distributor on how to solve this or try to compile from source via ghcup compile <version>.

Libnuma required

This was a bug in the build system of some GHC versions that lead to unconditionally enabled libnuma support. To mitigate this you might have to install the libnuma package of your distribution. See here for a discussion.

Compilation

Although this script can compile GHC for you, it's just a very thin wrapper around the build system. It makes no effort in trying to figure out whether you have the correct toolchain and the correct dependencies. Refer to the official docs on how to prepare your environment for building GHC.

Stack support

There may be a number of bugs when trying to make ghcup installed GHC versions work with stack, such as:

https://gitlab.haskell.org/haskell/ghcup-hs/-/issues/188

Further, stack's upgrade procedure may break/confuse ghcup. There are a number of integration issues discussed here:

https://gitlab.haskell.org/haskell/ghcup-hs/-/issues/153

Windows support

Windows support is in early stages. Since windows doesn't support symbolic links properly, ghcup uses a shimgen wrapper. It seems to work well, but there may be unknown issues with that approach.

Windows 7 and Powershell 2.0 aren't well supported at the moment, also see:

FAQ

Is ghcup really the main installer?

This is based on the Haskell survey results from 2022, which show that more than half of survey participants use GHCup: https://taylor.fausak.me/2022/11/18/haskell-survey-results/

Why reimplement stack?

GHCup is not a reimplementation of stack. The only common part is automatic installation of GHC, but even that differs in scope and design.

Why should I use ghcup over stack?

GHCup is not a replacement for stack. Instead, it supports installing and managing stack versions. It does the same for cabal, GHC and HLS. As such, It doesn't make a workflow choice for you.

Why should I let ghcup manage stack?

You don't need to. However, some users seem to prefer to have a central tool that manages cabal and stack at the same time. Additionally, it can allow better sharing of GHC installation across these tools. Also see:

Why does ghcup not use stack code?

GHCup started as a shell script. At the time of rewriting it in Haskell, the authors didn't even know that stack exposes some of its installation API
it doesn't support cabal installation, which was the main motivation behind GHCup back then
depending on a codebase as big as stack for a central part of one's application without having a short contribution pipeline would likely have caused stagnation or resulted in simply copy-pasting the relevant code in order to adjust it
it's not clear how GHCup would have been implemented with the provided API. It seems the codebases are fairly different. GHCup does a lot of symlink handling to expose a central bin/ directory that users can easily put in PATH, without having to worry about anything more. It also provides explicit removal functionality, GHC cross-compilation, a TUI, etc etc.

Why not unify...

...stack and Cabal and do away with standalone installers

GHCup is not involved in such decisions. cabal-install and stack might have a sufficiently different user experience to warrant having a choice.

...installer implementations and have a common library

This sounds like an interesting goal. However, GHC installation isn't a hard engineering problem and the shared code wouldn't be too exciting. For such an effort to make sense, all involved parties would need to collaborate and have a short pipeline to get patches in.

It's true this would solve the integration problem, but following unix principles, we can do similar via hooks. Both cabal and stack can support installation hooks. These hooks can then call into ghcup or anything else, also see:

...installers (like, all of it)

So far, there hasn't been an open discussion about this. Is this even a good idea? Sometimes projects converge eventually if their overlap is big enough, sometimes they don't.

While unification sounds like a simplification of the ecosystem, it also takes away choice. Take curl and wget as an example.

Why not support windows?

Windows is supported since GHCup version 0.1.15.1.

Why the haskell reimplementation?

GHCup started as a portable posix shell script of maybe 50 LOC. GHC installation itself can be carried out in about ~3 lines of shell code (download, unpack , configure+make install). However, much convenient functionality has been added since, as well as ensuring that all operations are safe and correct. The shell script ended up with over 2k LOC, which was very hard to maintain.

The main concern when switching from a portable shell script to haskell was platform/architecture support. However, ghcup now re-uses GHCs CI infrastructure and as such is perfectly in sync with all platforms that GHC supports.

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