Make Wingman produce user-facing error messages

[isovector]

Wingman now sends WindowShowMessage notifications in the case of errors, significantly clearing up the confusion around "why didn't that code action do anything?"

[michaelpj]

I think there's the ability for most requests to return an error with a code and message in case something went wrong during the request (e.g. see at the bottom of the executeCommand docs: https://microsoft.github.io/language-server-protocol/specification#workspace_executeCommand).

It seems like this would be a better way to signal failure? And I think it lets you give a message too. Not sure how to do this in our library, though.

[isovector]

result: any | null

what a type smh.

However, I'm currently returning the error as the response to the codeaction:

haskell-language-server/plugins/hls-tactics-plugin/src/Ide/Plugin/Tactic.hs

Line 103 in 19207ef

Left err -> pure $ Left err

but it doesn't show any messages in either vscode or vim/coc.

Maybe some LSP wizard could chime in here? @bubba do you know the right way to indicate errors to users?

[isovector]

@wz1000 chimes in from IRC:

│07:16:39    isovector | are there any LSP wizards? what's the right way to report a failing code action to the user?
│07:17:26       wz1000 | do you want the user to actually see the error?
│07:17:30    isovector | yes
│07:17:44       wz1000 | then 'showMessage'

which suggests I'm on the right track with this PR

[michaelpj]

Boo, that seems like a missed opportunity on the client side.

[michaelpj]

Y do people not think about the non-happy path??