Support workspaceFolders proposal

[mickaelistria]

microsoft/language-server-protocol#298 (comment) covers a discussion about allowing multi root/projects in language servers. This is not finalized in the protocol specification yet, but the vscode client api already covers it. This seems to be an important step forward and a major change, so it would be nice to start investigating support for it soon.

See https://bugs.eclipse.org/bugs/show_bug.cgi?id=526489 (PS: you should ask webmaster to remove bugzilla component if you're not using it).

[martinlippert]

Is there a way to get the related pull request accepted and a snapshot build that includes this up somewhere? I am eagerly waiting for this to make our language servers ready for the latest VSCode 1.18 release (which released support for multi-root workspaces).

[mickaelistria]

FYI, I've prepared a patch in LSP4E which takes advantage of this change in LSP4J to implement multi-root support, and it seems to work with JDT-LS https://git.eclipse.org/r/#/c/111750/
That doesn't validate everything though as JDT-LS ignores the "static" capabilities and mostly go through the registerCapability approach; but the operations to change workspaceFolder seem to work as expected between LSP4E and JDT-LS, using LSP4J as API on client side.

[svenefftinge]

closing since #133 is merged