Warns users about non-ghcup channels

[qxrein]

RESOLVES: #1225
example output

~: cabal run ghcup -- debug-info
Configuration is affected by the following files:
- cabal.project
[ Info  ] downloading: https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-0.0.9.yaml as file /home/qxrein/.ghcup/cache/ghcup-0.0.9.yaml
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--  0     0    0     0    0     0      0      0 --:--:-- --:--  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
[ Warn  ] Warning: The channel DefaultChannel uses a non-ghcup URL: URI {uriScheme = Scheme {schemeBS = "https"}, uriAuthority = Just (Authority {authorityUserInfo = Nothing, authorityHost = Host {hostBS = "raw.githubusercontent.com"}, authorityPort = Nothing}), uriPath = "/haskell/ghcup-metadata/master/ghcup-0.0.9.yaml", uriQuery = Query {queryPairs = []}, uriFragment = Nothing}
[ Warn  ] Warning: The channel StackChannel uses a non-ghcup URL: URI {uriScheme = Scheme {schemeBS = "https"}, uriAuthority = Just (Authority {authorityUserInfo = Nothing, authorityHost = Host {hostBS = "raw.githubusercontent.com"}, authorityPort = Nothing}), uriPath = "/commercialhaskell/stackage-content/master/stack/stack-setup-2.yaml", uriQuery = Query {queryPairs = []}, uriFragment = Nothing}
[ Warn  ] Warning: The channel CrossChannel uses a non-ghcup URL: URI {uriScheme = Scheme {schemeBS = "https"}, uriAuthority = Just (Authority {authorityUserInfo = Nothing, authorityHost = Host {hostBS = "raw.githubusercontent.com"}, authorityPort = Nothing}), uriPath = "/haskell/ghcup-metadata/master/ghcup-cross-0.0.9.yaml", uriQuery = Query {queryPairs = []}, uriFragment = Nothing}
[ Warn  ] Warning: The channel PrereleasesChannel uses a non-ghcup URL: URI {uriScheme = Scheme {schemeBS = "https"}, uriAuthority = Just (Authority {authorityUserInfo = Nothing, authorityHost = Host {hostBS = "raw.githubusercontent.com"}, authorityPort = Nothing}), uriPath = "/haskell/ghcup-metadata/master/ghcup-prereleases-0.0.9.yaml", uriQuery = Query {queryPairs = []}, uriFragment = Nothing}
[ Warn  ] Warning: The channel VanillaChannel uses a non-ghcup URL: URI {uriScheme = Scheme {schemeBS = "https"}, uriAuthority = Just (Authority {authorityUserInfo = Nothing, authorityHost = Host {hostBS = "raw.githubusercontent.com"}, authorityPort = Nothing}), uriPath = "/haskell/ghcup-metadata/master/ghcup-vanilla-0.0.9.yaml", uriQuery = Query {queryPairs = []}, uriFragment = Nothing}
===== Main ======
Architecture:  x86_64
Platform:      Linux UnknownLinux, 25.05
GHCup Version: v0.1.40.0-49-gc07d28ea

===== Directories ======
base:    /home/qxrein/.ghcup
bin:     /home/qxrein/.ghcup/bin
GHCs:    /home/qxrein/.ghcup/ghc
cache:   /home/qxrein/.ghcup/cache
logs:    /home/qxrein/.ghcup/logs
config:  /home/qxrein/.ghcup
db:      /home/qxrein/.ghcup/db
temp:    /home/qxrein/.ghcup/tmp

===== Metadata ======
default:     https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-0.0.9.yaml
stack:       https://raw.githubusercontent.com/commercialhaskell/stackage-content/master/stack/stack-setup-2.yaml
cross:       https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-cross-0.0.9.yaml
prereleases: https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-prereleases-0.0.9.yaml
vanilla:     https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-vanilla-0.0.9.yaml

[dfordivam]

@qxrein Thanks for the PR!
But I am afraid the solution implemented is not correct.
The urls being used by the ghcup via channelURL are in fact all official ghcup channels (they are hosted at haskell/ghcup-metadata repo)

In addition to using these official channels, the user could also provide (via ghcup config or command line options) a path to metadata file which does not have the "https://raw.githubusercontent.com/haskell/ghcup-metadata/" prefix. in this scenario we should warn users.

Also you may want to join the matrix chat (https://matrix.to/#/#ghcup:matrix.org) for more casual discussions on ghcup related dev

[qxrein]

ok

[qxrein]

this is working after introducing a random temporary channel to lib/GHCup/Version.hs.

~: cabal run ghcup -- debug-info
Configuration is affected by the following files:
- cabal.project
[ Warn  ] Warning: The channel StackChannel uses a non-official URL: https://raw.githubusercontent.com/commercialhaskell/stackage-content/master/stack/stack-setup-2.yaml
[ Warn  ] Warning: The channel TemporaryChannel uses a non-official URL: https://qxrein.com/custom-metadata/temporary.yaml
===== Main ======
Architecture:  x86_64
Platform:      Linux UnknownLinux, 25.05
GHCup Version: v0.1.40.0-50-g105f4be9

===== Directories ======
base:    /home/qxrein/.ghcup
bin:     /home/qxrein/.ghcup/bin
GHCs:    /home/qxrein/.ghcup/ghc
cache:   /home/qxrein/.ghcup/cache
logs:    /home/qxrein/.ghcup/logs
config:  /home/qxrein/.ghcup
db:      /home/qxrein/.ghcup/db
temp:    /home/qxrein/.ghcup/tmp

===== Metadata ======
default:     https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-0.0.9.yaml
stack:       https://raw.githubusercontent.com/commercialhaskell/stackage-content/master/stack/stack-setup-2.yaml
cross:       https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-cross-0.0.9.yaml
prereleases: https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-prereleases-0.0.9.yaml
vanilla:     https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-vanilla-0.0.9.yaml
temporary:   https://qxrein.com/custom-metadata/temporary.yaml

[dfordivam]

There are a few changes necessary, and please remove the code which is not used anywhere

[hasufell]

1. we do not want to emit a warning every time a download is issued... instead we want to emit a warning if a user adds a new channel (either via ghcup config add-release-channel or ghcup config set url-source)
2. nightlies are no exception... they are not maintained by GHCup, so we want to warn

[hasufell]

This will trigger on file:// URLs... which we don't want.