Show the type alias's name on hover

[MichaReiser]

Hovering a type alias currently reveals the aliased type.

We should show the type alias's definition instead, similar to pylance and resolve the documentation etc from the target

[Hugo-Polloli]

I'm going to try my hand at this over the weekend :)

[Hugo-Polloli]

Actually postponing working on this, before actually implementing anything I want to confirm the exact hover behavior, esp for PEP 695 type aliases.

Right now, with Pylance on Python 3.12, I see:

T = int       # hover T: `(type) T = int` + docs for int
type U = int  # hover U: `(type) U = TypeAliasType` + docs for int

class Test:
    t: T  # hover t: `(variable) t: int`
          # hover T: `(type) T = int` + docs for int

    u: U  # hover u: `(variable) u: int`
          # hover U: `(type) U = type[int]` + docs for int

The only consistent part is that the docs always comes from the aliased target. Also Pylance leaks internal representation (TypeAliasType / type[int]).

However, T = int and type U = int are not the same thing at runtime (the former binds T directly to int, while the latter is a TypeAliasType object), so I think it’s important to hint at that, but without weighing things down by mentioning TypeAliasType in the hover.

What I'm thinking for ty:

T = int       # hover T: `(type) T = int` + docs for int
type U = int  # hover U: `(type alias) type U = int` + docs for int


class Test:
    t: T  # hover t: `(variable) t: T (int)`
          # hover T: `(type) T = int` + docs for int

    u: U  # hover u: `(variable) u: U (int)`
          # hover U: `(type alias) type U = int` + docs for int


type Box[T] = list[T]

x: Box[int]  # hover x: `(variable) x: Box[int] (list[int])`
             # hover Box: `(type alias) type Box[T] = list[T]` + docs for list

• T = int presented as a plain type binding: (type) T = int.
• type U = int / type Box[T] = ... presented as first-class alias objects: (type alias) type U = int, etc.
• Variables always show user written-annotation (resolved-type).

Does this behavior match what you’d like for ty?