This is a complete example reproducing the weird behavior I saw in one of my projects.
I was checking whether the __info__/1 function was exported for a module as a way to check if a module exists.
I noticed that after a clean app start the behavior is fine, but after any recompile (even with no changes and recompile(force: true) in iex!) the behavior of function_exported?/3 would change to report the __info__/1 function no longer being exported.
I worked backwards and stripped the project of everything to get this minimal example.
To see the issue, run ./reproduce.sh and you should see something like this:
❱ ./reproduce.sh
+ mix clean
+ mix reproduce
Compiling 2 files (.ex)
Generated function_exported_bug app
Function Elixir.Foo.__info__/1 is exported.
+ mix reproduce
Function Elixir.Foo.__info__/1 is NOT exported.
+ mix reproduce
Function Elixir.Foo.__info__/1 is NOT exported.
+ mix clean
+ mix reproduce
Compiling 2 files (.ex)
Generated function_exported_bug app
Function Elixir.Foo.__info__/1 is exported.
~/d/function_exported_bug main• 2s ❱