Print aeson decoding error when metadata decoding fails #1113
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Previously the reported error is misleading ``` [ Info ] downloading: https://ghc.gitlab.haskell.org/ghcup-metadata/ghcup-nightlies-0.0.7.yaml as file /Users/bchinn/.ghcup/cache/ghcup-nightlies-0.0.7.yaml % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 606k 100 606k 0 0 964k 0 --:--:-- --:--:-- --:--:-- 963k [ Error ] [GHCup-00160] JSON decoding failed with: Aeson exception: [ ... ] Error in $: key "ghc" not found [ ... ] Consider removing /Users/bchinn/.ghcup/cache/ghcup-nightlies-0.0.7.yaml manually. ``` because this is the error when trying to decode the metadata as a stack format. The actual error is much better: ``` [ Debug ] Identified Platform as: Linux UnknownLinux, 24.05 [ Debug ] using local file: /home/matt/ghcup-hs/ghcup-nightlies-0.0.7.yaml [ Debug ] Decoding yaml at: /home/matt/ghcup-hs/ghcup-nightlies-0.0.7.yaml [ Debug ] Couldn't decode /home/matt/ghcup-hs/ghcup-nightlies-0.0.7.yaml as GHCupInfo, trying as SetupInfo: Aeson exception: [ ... ] Error in $.ghcupDownloads.GHC['9.11.20240719'].viArch['A_32']['Linux_Debian']['unknown versioning']: Failure in (Maybe VersionRange) (FromJSONKey)1:16: [ ... ] | [ ... ] 1 | unknown versioning [ ... ] | ^ [ ... ] unexpected 'v' [ ... ] expecting end of input or white space [ ... ] [ ... ] Consider removing /home/matt/ghcup-hs/ghcup-nightlies-0.0.7.yaml manually. [ Debug ] Decoding yaml at: /home/matt/ghcup-hs/ghcup-nightlies-0.0.7.yaml [ Error ] [GHCup-00160] JSON decoding failed with: Aeson exception: [ ... ] Error in $: key "ghc" not found [ ... ] Consider removing /home/matt/ghcup-hs/ghcup-nightlies-0.0.7.yaml manually. ``` Perhaps the fallback mechanism is a bit confusing and it would be better to have different command line options for ghcup/stack metadata. The bad error will still be reported to a user if they encounter malformed metadata.
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I decided against that. You can combine stack metadata with GHCup prereleases metadata. I don't see how that would work well with cli switches. |
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Indeed it's bad ergonomics that the primary error is the stack decoding. The aeson error reporting is awful in general. I'm open to more radical changes here, such as collecting the errors of all tried alternatives (at least "top-level"). I'm thinking there should be a combinator for this. |
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Anything blocking this patch being merged? |
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Previously the reported error is misleading
because this is the error when trying to decode the metadata as a stack format.
The actual error is much better:
Perhaps the fallback mechanism is a bit confusing and it would be better to have different command line options for ghcup/stack metadata. The bad error will still be reported to a user if they encounter malformed metadata.