Improve diagnostics

[Arthurm1]

Is your feature request related to a problem? Please describe.

BSP and LSP have 3 diagnostic fields that are (almost) ignored by Metals: tags, codeDescription and relatedInformation

Describe the solution you'd like

Could Metals pass on these 3 fields from BSP to LSP?

BSP spec for Diagnostic is here
LSP spec for Diagnostic is here
Metals code is here

Metals could pass on the fields and still enhance the tags with the current deprecation check based on code if the BSP server isn't passing tags back.

There are support flags sent by the LSP client...
capabilities#textDocument#publishDiagnostics#codeDescriptionSupport
capabilities#textDocument#publishDiagnostics#tagSupport
capabilities#textDocument#publishDiagnostics#relatedInformation
I'm not sure if these flags should be checked before populating the info or whether a client will just ignore any additional information. Documentation here

Describe alternatives you've considered

The diagnostics are pretty good as is but this would be icing on the cake.

Additional context

This was also requested in #309 but only for the deprecated tag. These additional fields would be helpful as well although I've not had to use the relatedInformation field.

Search terms

Diagnostics deprecated unused codedescription relatedinformation

[tgodzik]

Wouldn't scalameta/metals#7294 achieve what you want?

[Arthurm1]

LGTM.

Not sure if there are any issues with version mismatches. i.e. newer version of Bloop supplies a field in Diagnostic that an older version of VSCode doesn't have. But I imagine the clients just ignore additional fields?

[tgodzik]

LGTM.

Not sure if there are any issues with version mismatches. i.e. newer version of Bloop supplies a field in Diagnostic that an older version of VSCode doesn't have. But I imagine the clients just ignore additional fields?

That's the usual behaviour, I haven't seen issues with more fields only ever with wrong ones.