support inlay hints

[Eskibear]

It's available in IntelliJ IDEA,
https://www.jetbrains.com/help/idea/inlay-hints.html

Supported in TS/JS since vscode v1.60

See: https://code.visualstudio.com/updates/v1_60#_inlay-hints-for-javascript-and-typescript

Proposed API in VS Code:
https://github.com/microsoft/vscode/blob/997228d528d687fd17cbf3ba117a0d4f668c1393/src/vs/vscode.proposed.d.ts#L1773-L1793

LSP proposal:
microsoft/language-server-protocol#956

[rgrunber]

It's also supported in Eclipse since 4.12 (2019-06) https://www.eclipse.org/eclipse/news/4.12/jdt.php#parameter-name-codemining.

https://git.eclipse.org/c/gerrit/jdt/eclipse.jdt.ui.git/tree/org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/codemining/CalleeJavaMethodParameterVisitor.java

I don't think we can use the class since it's in UI and ICodeMining is tied to some UI rendering elements. However the AST logic is pretty straightforward to copy over, or we could refactor the relevant parts we need in JDT.

[jayy2kok]

I have adopted VS Code for full time java IDE, I love it, just this one feature I am missing.

[rgrunber]

I think we should watch out for things like https://bugs.eclipse.org/bugs/show_bug.cgi?id=568844 , and maybe look at possible solutions. The jumpiness is caused when a method temporarily can't be resolved to a proper signature (due to syntax error?) and then switches to resolved. The effect is annotations flickering which affect the user's ability to type.

[jdneo]

Update: inlay hint is available as client side API in VS Code 1.65.0.

Maybe we can first make a client side implementation. I can volunteer for that. :)