"0.001% of the time, I wanna know every time 👉😎👉"

Yeah, I get that. But are we talking about during development (which is why we're choosing between C and something else)? In that case, you should be running instrumented builds, or with debug functionality enabled. I agree that most programs just fail and don't tell you how to go about enabling debug info or anything, and that could be improved.

For the "Permission Denied" example, I also assume we're making system calls and having them fail? In that case it seems straight forward: the user you're running as can't access the resource you were actively trying to access. But if we're talking about some random log file just saying "Error: permission denied" and leaving you nothing to go on, that's on the program dumping the error to produce more useful information.

In general, you often don't want to leak more info than just Worked or Didn't Work for security reasons. Or a mix of security/performance reasons (possible DOS attacks).

It's more of an ABI thing though, C just doesn't have error handling.

And if you do exception handling wrong in most other languages, you hamstring your performance.

Errors and return values are, and should be, different things.

That's why errno and return value are different things.