Fix KI protection decorator

[A5rocks]

This should fix the trio.Lock issue in #2775.

[codecov]

Codecov Report

Merging #2781 (2933c6d) into master (1c15500) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2781   +/-   ##
=======================================
  Coverage   98.94%   98.94%           
=======================================
  Files         113      113           
  Lines       16919    16920    +1     
  Branches     3050     3050           
=======================================
+ Hits        16741    16742    +1     
  Misses        123      123           
  Partials       55       55           

Files Changed	Coverage Δ
trio/_core/_ki.py	100.00% <100.00%> (ø)

[apollo13]

Can confirm that it fixes my Lock issue.

[TeamSpen210]

Makes sense as a solution, I had a little difficulty too when doing this originally. Actually though, it'd be better to use a typevar with bound=Callable, instead of ParamSpec - in that case, the checker can preserve the entire function type, including things like overloads.

[jakkdl]

though if teamspen's suggestion of a typevar works that sounds like it would be even better

[A5rocks]

Makes sense as a solution, I had a little difficulty too when doing this originally. Actually though, it'd be better to use a typevar with bound=Callable, instead of ParamSpec - in that case, the checker can preserve the entire function type, including things like overloads.

I'm not entirely sure this is possible due to use using *args: P.args, etc. inside. It might be possible though? And that might be better external-facing behavior so probably worth a # type: ignore if CI running atm says it doesn't work.