Support for GHCup "mirrors" configuration

[ruifengx]

先决条件 (Prerequisites)

• 我已确认该事宜从未在 其他 issues 中讨论过。
  I have checked that my proposal has not been discussed in other issues.

• 我已仔细阅读 请求新镜像前必读。
  I have CAREFULLY read the mirroring rules.

修改或删除的原因 (Reasons of the modification or removal)

This is the latest version of the official configuration guide:

https://www.haskell.org/ghcup/guide/#mirrors-proper

To use this method, GHCup expects to find the files under $host/$pathPrefix/haskell/ghcup-metadata/. The mirror, as it is currently configured, puts all the files under ghcup/ghcup-metadata/.

配置方法 (Configuration method)

The easiest solution AFAIK is to serve the same set of files under both ghcup/haskell/ghcup-metadata/ (for mirrors support with $pathPrefix = ghcup) and ghcup/ghcup-metadata/ (for backwards compatibility). I think the server can be configured to simply redirect one URL to the other.

修改后的镜像大小 (Mirror size after modification)

No change expected

备注 (Note)

No response

[iBug]

https://mirrors.ustc.edu.cn/ghcup/haskell/ghcup-metadata/

[taoky]

Please consider contributing to: https://github.com/ustclug/ustcmirror-images/blob/master/ghcup/ghcupsync.hs

Just add a symlink is OK. I'm not very experienced in Haskell.

[ruifengx]

https://mirrors.ustc.edu.cn/ghcup/haskell/ghcup-metadata/

I believe the files are not structured as GHCup expected.

GHCup tries to pull https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-0.0.9.yaml (note the branch name master), but ghcup-0.0.9.yaml is currently directly put under ghcup/haskell/ghcup-metadata in the mirror.

Please consider contributing to: https://github.com/ustclug/ustcmirror-images/blob/master/ghcup/ghcupsync.hs

Thanks for the pointer. I will look into this.