completion performance: toURI is expensive on Windows

[Eskibear]

In my past experiments, JDTUtils.toURI can take 20% - 80% of completion time. Below is an example of the call tree, when I press "f" for completion in spring-petclinic project. Completion list mainly include some foreach snippets and a lot of Types starting with letter F.

I'm using a relatively powerful PC, so focus more one the percentage instead of absolute millis.

The uri is filled in each completion item's data field, and is used in completion/resove request, to get the corresponding complilation unit. E.g.

"data": {
                "decl_signature": "Lorg.springframework.boot.SpringApplication;",
                "pid": "4",
                "rid": "3",
                "uri": "file:///C:/Users/admin/projects/spring-petclinic-main/src/main/java/org/springframework/samples/petclinic/PetClinicApplication.java"
            }

When I step into it, I find most time is spent on "slashy" the uri, where it adds trailing "/" if it's a directory.

I don't think any directory would be used here in CompletionItem.data.uri, so a simple improvement coming to my mind is to skip the slashy here, by not using java.io.File.toURI.

[Eskibear]

Or a simple and effective way is, to avoid computing URI of the same compilation unit for all the CompletionItems.

[vogella]

Awesome. Can you point back to the Gerrit / Bug report in JDT core which fixed that?

[rgrunber]

Although the name implies it originates from JDT, this was a performance improvement on our end. Changes like https://git.eclipse.org/r/c/jdt/eclipse.jdt.core/+/184535 on the other hand, have benefited both JDT-LS and JDT though.

[vogella]

Thanks @rgrunber for the info