report error for unsolved type variables in function calls

[KotlinIsland]

• resolves: report an error when a type variable cannot be resolved #1499

• depends on: remove unused generic from argparse._ActionsContainer.add_argument python/typeshed#15585

[DetachHead]

• resolves: report an error when a type variable cannot be resolved #1499

the example from that issue still doesn't report an error:

a = []

[DetachHead]

the error message is pretty confusing in this case:

Type variable "T" has no solution; consider providing it explicitly

maybe for list/set/dict/etc. literals it should give an example of how to fix it, eg:

Type variable "T" has no solution; consider providing it explicitly (eg. list[int]())

maybe that can be a diagnostic addendum

[beauxq]

I don't think I like suggesting
a = list[int]()
when
a: list[int] = []
would have better performance.

[KotlinIsland]

@DetachHead ci failed for some flake i think, wanna review?

[DetachHead]

that can happen if you push the same commit multiple times, it tries to publish a canary version that already exists

[DetachHead]

i think the primer has raised some false positives, or at least scenarios that need investigating

[beauxq]

I'm not sure I like this name.

"Solving" a type variable is a perspective of the type-checker implementer, that the type-checker user shouldn't need to think about.

The user doesn't need to think about "solving" things, or "solutions".

This kind of seems like something for the family of reportUnknown... rules.
reportUnknownTypeVar?

[DetachHead]

while the term is possibly confusing since type checkers seem to have different words for it (pyright uses the word "specialize" but idk if that term is unique to pyright), i don't consider the actual resolving of a type var to be an implementation detail. the user should be able to clearly tell when using a function or class with a generic whether that generic was able to be inferred or not, regardless of what word is used to describe that process.

i agree reportUnknownTypeVar sounds like a better name, and is more consistent with other similar rules