implement textDocument/didSave

[prabirshrestha]

In vim-lsp I automatically didSave when a file is saved. Would be good if this was implemented.

https://github.com/Microsoft/language-server-protocol/blob/master/protocol.md#textDocument_didSave

[rcjsuen]

@prabirshrestha I don't understand. The protocol states the following:

The document save notification is sent from the client to the server when the document was saved in the client.

This is a notification from the client to the server. I don't think this is something for the language server to implement.

[prabirshrestha]

My bad. I was sending a request instead of notification and was getting not supported error by the server. Sorry for the noise.

[rcjsuen]

@prabirshrestha Thank you for checking, Prabir. :)

You should also check if the language server you are connected to is actually interested in that event before sending it. Check out the ServerCapabilities.textDocumentSync section in the protocol.

The ServerCapabilities.textDocumentSync.save setting may not be set. In that case, you don't want to waste resources sending something over the wire if the language server you are talking to isn't even interested in the that event.

[prabirshrestha]

Seems like I need to update vim-lsp. Filed a bug to track this. prabirshrestha/vim-lsp#29. Thanks for the details.

[rcjsuen]

@prabirshrestha Actually, I think I might have been wrong about when a client should be sending that notification to the server. Sorry about that.

I think a client might have to always send the notification unless the ServerCapabilities.textDocumentSync.save value is defined and set to false. Version 2.x of the protocol had the textDocument/didSave notification but it wasn't possible for the server to declare whether it was interested in the event or not so I think the expectation is that the notification will always be sent to the server unless it explicitly says it isn't interested in it.

For example, my language server only sets a TextDocumentSyncKind number for its ServerCapabilities.textDocumentSync property but VS Code still sends me textDocument/didSave notifications although it doesn't include the document's text in the notification.

[rcjsuen]

@prabirshrestha Actually, ServerCapabilities.textDocumentSync.save won't be set to false because it's a SaveOptions object and not a boolean. So I think the correct behaviour would be for the client to not send the notification only if that property is undefined.

I could be wrong of course so you may want to open an issue and ask for clarifications.

Sorry for all the confusion that I'm causing!

[prabirshrestha]

Filed an issue at microsoft/language-server-protocol#288.