Potential improvements to error reporting

[AndrewRadev]

I've started experimenting with LSP (I'm new to using and interacting with language servers) and ran into some difficulties understanding the errors. I tried launching the example with cargo run --example goto_def and just copy-pasted some jsonrpc messages and it didn't work out. Here's how an interaction like this might look on master:

% cargo run --example goto_def  
starting generic LSP server
foo
Error: ProtocolError("expected initialize request, got Err(RecvError)")

After doing some digging I can see that the RecvError should have some more information, but the way that it's being printed doesn't show me a lot of it. Here's how the same interaction is rendered in this branch:

% cargo run --example goto_def
starting generic LSP server
foo
Error: ProtocolError("expected initialize request, got error: receiving on an empty and disconnected channel")

So now I can at least guess that the problem doesn't have to do with parsing, but with the way the input is sent, and it would have to be the first thing to fix (like piping the commands by using a file).

I think this is an improvement, but there might be different ways to make it better -- let me know. I'd also consider using unreachable! in cases where a Message::Request is expected, but a Message::Response is given, for example.

[AndrewRadev]

Not sure what's up with the build, seems to be failing on an attempt to push a release (with --dry-run):

$ git push --tags --dry-run
remote: Permission to rust-analyzer/lsp-server.git denied to github-actions[bot].
fatal: unable to access 'https://github.com/rust-analyzer/lsp-server/': The requested URL returned error: 403

[bjorn3]

LGTM Could you please rebase @AndrewRadev?

[AndrewRadev]

@bjorn3 I've rebased my changes on top of master. Wasn't 100% sure if I'd gotten everything right, but it compiles, tests pass and the example I've left in the PR description seems to work as before.

[bjorn3]

Sorry for the long wait! It must have slipped through. I found this PR while going through all open PR's in the rust-analyzer organization.

bors r+

[bors]

Build succeeded:

• Rust