What's the expected behaviour of CompletionList.isIncomplete=false when the user presses backspace?

My understanding is that if IsIncomplete=true, the client will not cache results and must go back to the server whenever the user types a character (this allows the server to return a partial set of results).

Currently in Dart we use IsIncomplete=false - eg. we give the full list to VS Code and allow it to filter client side.

There has been an assumption that I don't think is well described in the spec, relating to whether the client should supply all possible completions given the current prefix or all possible completions for the current location regardless of prefix.

For example, let's say my completion list simple has:

• one
• two
• three

If the user invokes completion where ^ is here:

print(on^

If the server is using IsIncomplete=false (eg. it's providing the full list), should it include two and three here, on the assumption that the client will not call the server again even if the user hits backspace, or should it assume that the client-side filtering is only for typing forwards?

The spec is a bit vague on this (it's not clear what "Further typing" covers, and "recomputing" is also a little vague - I presume it means "the client should re-request completions from the server").

This list it not complete. Further typing should result in recomputing this list.

If pressing backspace is intended to re-call the server even when IsIncomplete=false, then significant gains could be made for us by filtering based on the prefix on the server.

Thanks!

Start with the CompletionList specification passage quoted in the issue, then review the 14-comment thread for the unresolved interpretations of IsIncomplete=false, client-side filtering, and backspace. Done means the expected client behavior is decided and documented clearly in the protocol specification.