Dispose LSP's output channel on restart

[plemarquand]

When restarting SourceKit-LSP its output channel was not disposed, which caused a new entry to be added to the output channel list without removing the old one.

Fixes #839

[adam-fowler]

This is kind of dodgy, in that we are assuming the VSCode language client never calls the dispose on the outputChannel. Looking through the language client code it should be calling it, so I am a little confused as to why this call is needed. https://github.com/microsoft/vscode-languageserver-node/blob/0226f6cd925d279dda2b777d25c5b69518ac0035/client/src/common/client.ts#L1414

[plemarquand]

After some digging I understand what is happening here, and it does seem to be a bug in vscode-languageclient. The flow is:

• The initial client is created, client's output channel ("OC1") is created.
• User runs "Restart LSP Server"
• client.stop is called, "OC1" is disposed, client._outputChannel is set to undefined
• Cleanup continues, and the spawned LSP process is terminated
• This finally block executes, listening for the LSP process to exit.
• LSP exits with code 0, which is then logged here.
• The outputChannel getter, seeing that this._outputChannel is undefined due to previous disposal, creates a new output channel ("OC2") that replaces the one that was disposed.
  • This output channel is what I'm disposing in this patch. Without this code, OC2 never gets disposed.
• Finally, we create a new client, which creates a new output channel "OC3".

This leaves us with one more output channel than we started with.

[adam-fowler]

After some digging I understand what is happening here, and it does seem to be a bug in vscode-languageclient. The flow is:

Do you want to add an issue for the vscode language client? Oh and add a comment here detailing the issue and that it should be reverted once a fix is in vscode-language-server

[plemarquand]

Sounds good, I'll create that issue once I have received internal approval and link it back to here.

[plemarquand]

Created https://github.com/microsoft/vscode-languageserver-node/issues/1496 to track the root cause in vscode-language-server-node.