Credo.Check.Readability.FunctionNames potential false positives for non-sigil functions beginning with "sigil_"

[brettbeatty]

Environment

• Credo version (mix credo -v):

  $ mix credo -v
  1.7.10-ref.nobranch.nocommit+uncommittedchanges
  

• Erlang/Elixir version (elixir -v):

  $ elixir -v
  Erlang/OTP 27 [erts-15.1.1] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [jit:ns]
  
  Elixir 1.17.3 (compiled with Erlang/OTP 27)
  

• Operating system: Ubuntu 24.04

What were you trying to do?

I have a sigil with a supporting private function. I prefixed the private function name with the sigil name, and when I updated credo it flagged it for not being in snake case.

Expected outcome

No errors

Actual outcome

┃ [R] ↗ Function/macro/guard names should be written in snake_case.
┃       lib/my_app.ex:6:8 #(MyApp.sigil_z_do)

It seems to happen with any function beginning with "sigil_" that is not in fact a sigil.

┃ [R] ↗ Function/macro/guard names should be written in snake_case.
┃       lib/my_app.ex:10:7 #(MyApp.sigil_do_something_else)

It seems a little odd to name a non-sigil function with a "sigil_" prefix, but as far as I'm aware there's nothing wrong with it.

Seems related to #1146