Provide client-side snippet until language server is ready

[jdneo]

This PR fix #684

• postpone the client side snippet provider dispose time when the server is ready.
• dispose the provider to make sure the items will be removed in the completion list when disposing happens.

Signed-off-by: Sheng Chen[email protected]

[testforstephen]

Tried it and this PR didn't solve the problem completely. There is another factor that causes the code snippet not to work.

On the jdt.ls server side, it registers capability for "textDocumement/completion" after initialized, which would cause both the client and server side to declare the completion provider before the server was full ready, and the server side would block the entire completion from working.

From the perspective of LSP, initialized means JLS is ready to accept request, and it will send completion request to JLS even though it's not really ready. And if multiple Java completion providers exist at the same time, VS Code will wait for all of them to be finished before returning the results. The slower one will determine the completion performance.

[jdneo]

This is a great finding! Currently we register the capabilities earlier than the server is able to dealing with those request. During this time window, if user starts to typing or doing other operations, a lot of requests sending from client to server and queued there, which makes the import time becomes 'longer'. Server needs to treat with those queued request but most of them are out-of-date.

[testforstephen]

There is a feature request microsoft/vscode#107343 about showing results from different completion providers incrementally, but it's still under discussion.

if we want to mitigate the issue for now, we need to delay registering completion capability on the server side until the language server is actually ready.

[testforstephen]

It's possible to show duplicated snippet in completion list when lightweight server is up but standard server is still loading. both lightweight server and client-side snippet provide same snippets.

[testforstephen]

It works fine with the latest commit. Feel free to merge this PR once eclipse-jdtls/eclipse.jdt.ls#1979 is merged.