Support for completionItem/resolve

[mickaelistria]

For Maven extension, we'd like to offer completion item documentation asynchronously (as it requires to read the pom which we cannot do for all proposals or completion would take to long).
Does the extension provide a way to "resolve" a completion item? I couldn't find an appropriate method.

[angelozerr]

No there is no possibility to do that, because today we need not that (performance are correct for any extension like XSD, DTD completion, etc).

Any contribution are welcome!

To do that, I suggest that you implement completion/resolve like

lemminx/org.eclipse.lemminx/src/main/java/org/eclipse/lemminx/XMLTextDocumentService.java

Line 175 in e314411

public CompletableFuture<Either<List<CompletionItem>, CompletionList>> completion(CompletionParams params) {

The XMLLanguageService should have a new method like doResolveCompletionItem which call the same method in https://github.com/eclipse/lemminx/blob/master/org.eclipse.lemminx/src/main/java/org/eclipse/lemminx/services/XMLCompletions.java

The doResolveCompletionItem must loop for ICompletionParticipant like

lemminx/org.eclipse.lemminx/src/main/java/org/eclipse/lemminx/services/XMLCompletions.java

Line 491 in e314411

for (ICompletionParticipant participant : getCompletionParticipants()) {

and call the new method ICompletionParticipant #resolveCompletionItem (by default it should return null)

It's the main idea, if you need some more help, please ask me.

[mickaelistria]

This has become more important in lemminx-maven since adoption of Maven Central Search engine that doesn't provide description in its response; so we need to download the pom to show description and this shoudl be part of a completionItem/resolve.
cc @vrubezhny

[angelozerr]

Any contribution are welcome!

[angelozerr]

We need this resolve completion support to fix redhat-developer/vscode-xml#679