Provide assistance for writing an impl block

[RalfJung]

When I am at a type, I can select a "generate impl" assist and it will generate a block right below the type. That's useful, but often I am somewhere else in the project (might not even be the same file), and I want to generate an impl block here. Would be great if there was some way to get the assist there as well. :)

What I usually try is to write impl TypeName, and then my hope would be that (a) I get auto-complete (including auto-import) for the type name, and (b) I can then select an assist to generate an impl block, and it will turn this into

impl<'a, T: Bound> TypeName<'a, T> {
  /* cursor here */
}

[lnicola]

A better UX might be to write impl TypeName and get a completion for the whole thing 🙂.

[ShoyuVanilla]

I'll give this a try
@rustbot claim

[ChayimFriedman2]

@ShoyuVanilla Are you still working on this?

[ShoyuVanilla]

No, I was just waiting for #18032 to effectively work on assist things. You could work on this if you like 😄

[ChayimFriedman2]

@rustbot claim

[ChayimFriedman2]

@rustbot release-assignment

I still intend to work on this, but as a diagnostic with quick fix, and this diagnostic requires #18074 and follow-ups, which is quite big work. So in order to not create false hopes and not block anyone who would like to want on this, I'm unassigning for now.

[ChayimFriedman2]

Now after we have diagnostics for type, I can come back to work on this.

@rustbot claim