JSON decoding failed [GHCup-00160]

This error is most common when GHCup tries to fetch the metadata file that contains information about available tool versions and binary distributions. This is done when GHCup starts, so basically any command such as list, tui, install, etc. can throw this.

Potential underlying causes for this errors are:

No internet connection
Unreliable disk or Internet leading to a corrupted file
Non-functional curl or wget (users have reported difficulties when these tools are installed through snap)
Malformed metadata file, indicating an issue in the ghcup-metadata repository

As an example with no internet connection, GHCup will fail to list available tools:

$ ghcup list
[ Info  ] downloading: https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-0.0.7.yaml as file /home/hasufell/.ghcup/cache/ghcup-0.0.7.yaml
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0curl: (6) Could not resolve host: raw.githubusercontent.com
[ Warn  ] Could not get download info, trying cached version (this may not be recent!)
[ ...   ] If this problem persists, consider switching downloader via:
[ ...   ]     ghcup config set downloader Wget
[ Error ] [GHCup-00160] JSON decoding failed with: YAML exception:
[ ...   ] Yaml file not found: /home/hasufell/.ghcup/cache/ghcup-0.0.7.yaml
[ ...   ] Consider removing /home/hasufell/.ghcup/cache/ghcup-0.0.7.yaml manually.
[ ...   ]

If you use ghcup --metadata-fetching-mode=Strict list, then you’ll likely receive error GHCup-05841 instead.

The best way to debug this is to try to fetch the metadata manually:

cd "$(ghcup whereis cachedir)"
curl https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-0.0.7.yaml

Alternatively try with wget:

cd "$(ghcup whereis cachedir)"
wget -O- https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-0.0.7.yaml

If the download fails, your curl/wget installation might be broken. On Linux, make sure you’ve installed these from your package manager and not via snap, Flatpak or AppImage. GHCup neither recommends nor supports those tools. On Windows, make sure you use curl.exe and not curl (which is a cmdlet) when testing. It should be pre-installed.

If the download succeeds, but the error persists, try examining the file and verify that it’s valid YAML:

cat "$(ghcup whereis cachedir)/ghcup-0.0.7.yaml"

Fix your connection issues, make sure to delete $(ghcup whereis cachedir)/ghcup-0.0.7.yaml and then try again. If you believe this is not a connection issue and there’s something wrong with the file, please open an issue here.