They were replying to a person who says “it’s almost always wrong for library functions to log anything”. Not just errors.

If it’s not your code how is a log useful vs returning an error?

Even relatively complex operations like say convert this document into a PDF etc basically only has two useful states either it worked or something specific failed at which point just tell me that thing.

Now independent software like web servers or database can have useful logs because they have completely independent interfaces with the outside world. But I call libraries they don’t call me.

That’s a very simple operation. Try “take these 100 user generated pdfs and translate all of them”. Oh, “cannot parse unexpected character 0x001?” Cool beans, I wish I knew more.

That’s ok, I’ll just check the log. 50MB of ‘This is my happy place.’ followed by a one liner “cannot to parse unexpected character 0x001?’

Any library can do a bad job here, that doesn’t come down to logging vs error messages.

The unspoken assumption you are making is that anyone who would disagree with your philosophy on this is incompetent.

Being incorrect doesn’t imply general incompetence.

Your statement that logging would contain zero useful information indicates an assumption of incompetence.

No, I’m only saying a useless error code and a useless log are both possible. Either could be useful or they could both be useless because the creator was actively malicious etc. Thus, the possibility of a useless error code doesn’t inherently mean a log would improve things.

Really the only thing we can defiantly say is when both approaches are executed well it’s harder to use log entries in your code. If something returns an error that’s tied to a specific call to a specific bit of code, where a log entry could in theory be from anything etc.

Trace can become so voluminous that it is switched on only on a need basis which can be too late for rare events. Also trace level as more a need to use debug tool tends to be less scrutinized for exposing sensitive data making it unsuitable for continuous operation or use in live production.