Incremental update in properties editor completion is broken

[kdvolder]

Describe the bug

Incremental update where completions 'update as you type more letters' seems to be broken in Eclipse (maybe also in vscode, but haven't confirmed / tried that).

I think it is not correctly handling the case where a large number of results is initially incomplete. When we continue typing this incomplete list is filtered down further, but for correct operation it should instead request a new list of completions, otherwise the most relevant completions may be missed.

To Reproduce

1. Import attached sample project
   demo.zip

2. open application.properties

3. slowly type 'some.' (i.e one letter at the time waiting each time to get completions / updated completions as you type).

Observe:

• there is supposed to be a property called 'some.name' but it isn't suggested. Some other things are suggeste and they are 'correct matches' but they are really poor matches (i.e. fuzzy mathces with many / big gaps between the letters that were typed).

To see the behavior that should be expected... do the following:

1. press ESC to close the completion window
2. type CTRL-space to invoke completion request again (so you immediately get completions for some. in a single, non-incremental completion request).

Observe:

• now that we get the completion in a 'non-incremental' way we get some.name suggested at the top of the list.
  This is also the result we would have wanted/expected to see when we type slowly/incrementally. (i.e. the speed of typing should not really impact the suggestions that you get in the end).

[kdvolder]

Relevant information for whoever picks up investigation and fixing this.

This most likely has something to do with the CompletionList.isIncomplete (see https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#completionList) property in a completion result. When the language server is returning an imcomplete list of results (typically because the actual number of results would be too large), this attribute must be set to true.

We used to set this property, but perhaps a regression was introduced somewhere that no longer sets it, or perhaps a regression in lps4e / lsp4j no longer processes that attribute properly.

[kdvolder]

I tried this in vscode and it works properly there. So maybe this means its not a bug in our LS but rather something in lsp4j lsp4e.

[kdvolder]

Still a problem today, during STS 4 testing for 4.16.1