Handle `$/setTraceNotification` message about lsp4j HOT 7 CLOSED

Whether this should go to the LSP was discussed here microsoft/language-server-protocol#109

Maybe we should have an additional interface for such things that clients can optionally implement. Longterm we will need to use additional interfaces for LSP extensions anyway to avoid breaking clients.

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If it is possible for a client to send notification messages not strictly defined by the protocol, the current way of handling it in lsp4j... i.e. crashing the server... is not very nice.

As mentioned in the link above by @dbaeumer:

$ messages should/could be ignored since they depend on the implementation capabilities on the server. That is why I used the $ prefix.

We've implemented our own 'wrapper' to catch these errors, log them and ignore these. But perhaps lsp4j should just ignore these unknown messages by default?

from lsp4j.

I think they should at least be logged with warn level.

from lsp4j.

I think they should at least be logged with warn level.

Agreed. Especially if they are totally 'unknown' notification messages. However, if its a specific message, like say $/setTraceNotification, then perhaps a decision can explicitly be made that that particular type of message is not one the server should want to handle. Then, dropping it silently might be okay too.

What I mean is, unless the warning serves a purpose, like, informing someone that they need to make a decision (whether they do or do not want to handle it), a warning seems right. If however the decision has already been made, then the warning is just a nuisance.

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I changed the UnsupportedOperationExceptions to log warnings.

@dbaeumer wrote:

$ messages should/could be ignored since they depend on the implementation capabilities on the server. That is why I used the $ prefix.

Should we include this behavior in LSP4J, i.e. suppress the log warnings in case the method name starts with $?

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I would prefer to not do it.

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Then we can close this issue.

In order to explicitly ignore a certain type of message, one must add a @JsonNotification annotated method with an empty implementation to the service class.

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