Show inferred types as inline code

I’ve been writing some Rust code and I’ve appreciated the inline declarations of inferred types. It makes reading and working with code much easier. This is apropos Dart where some repositories enforce the explicit declaration of types whereas others don’t.

Here is an example of the Rust extension showing inferred types (and parameter names but this issue isn’t asking for that):

: &Option<Rc<Node<i32>>> is the inferred type of result. It doesn’t exist in the file but it would be valid code had it been written there. The inline hint is itself valid code, which is important.

So in Dart’s case it would look like this:

final x = add(1, 2);

becomes:

final int x = add(1, 2);

Where int doesn’t exist in the code but is displayed as above as if it was.

[DanTup]

The only question I have is if we should show var int x1.

I think ideally we should replace var with int, but we’re not able to do that. LSP only allows us to provide a Position and not a Range. I don’t think not being able to replace it should avoid us showing the type though (the purpose of this feature is to let the user see types that aren’t explicitly in the code), so I think this is all we have.

I do generally think we should try to stick to “valid code” where possible though, just not at the expense of not including a type.

[DanTup]

I thought we already had an issue for this, but can’t find it (perhaps remembering #3609 which is for parameter names).

Started on this, right now it’s just the labels:

But I’ve filed #4156 to see whether we can support showing the type dartdocs on mouseover too.

The change is in the analysis server so will ship as part of an SDK.