[feature] TypeGuard/TypeIs functions must have at least 1 positional parameter. If it's a method, it must have at least 2 positional parameters.

[yangdanny97]

Describe the Bug

See the sandbox link for examples of the cases we should cover.

We should add the check to this function:

pyrefly/pyrefly/lib/alt/function.rs

Line 166 in c247d45

let mut is_classmethod = false;

The return type is calculated here:

pyrefly/pyrefly/lib/alt/function.rs

Line 376 in c247d45

let ret = self

Once we get the return type, we can see if we need to have 1 or 2 params based on what kind of function it is, and emit a BadFunctionDefinition error if it doesn't have the required number.

Once this task is done, add an integration test to pyrefly/lib/tests/narrow.rs, run test.py, and commit any generated changes.

Sandbox Link

https://pyrefly.org/sandbox/?code=GYJw9gtgBALgngBwJYDsDmUkQWEMoBUAUEQMRQB8UAksFAIayICmUaArvSACZTDsoAxjCRgUmAM6ZsAG2YRmKGM170p9cagkwNg1gpgALML1xRBMtRLKUoB49wA0sQ62BIQ2qDglIRY+hkGEA4FJTt6BCkYMBdWCWZBMV4ELnoDZhAbKgAKemBlEChAHAIEmWBAXAIoM2KLCQqASgA6EgsrKABhAC4iKD6obmY6GDQAfQBGHLLgBqgAWioAFRYAcU4eAG1UGABdLr7yADkwfAB5AGle-uuQZhh2EHEAMUCEkmuAATaJCXsTK76g2GYwATDk6rMFlBlghmGsuNwtko9gcoMczpdrjc7g9nq9mCRyItXAlgm5UASgbAxgBmHLAMBgSFLVbrRHbPYAqC3e6PKAvGRvKkjUYAFnpjOcACMuMzoayEUjdj1sby8YLKUNqaMAKwSsDOAD0cphcLZSs5qtx-PxJCIwrGADYciaFZsOfsoEcTlALlyedaBUKtSKAOw5AjOBlM+Ys2Hw93Iz3ejFRxmSKAAa2YcAA7rhuHMxDI4P6cXygwSgA

(Only applicable for extension issues) IDE Information

No response