But the thing it does (fill out a fixed sized buffer without caring about NUL-termination) is not at all what you'd want from a safety feature.
If you look at this function assuming it's a safety feature, that's a huge surprise, and indeed if you were skimming you might miss what it does because (in the context of "it's a safety feature") this is an insane choice. "Why would you do that?". Well, because it's not a safety feature.
The perf cost isn't what you'd expect from a safety feature either. Suppose we have a 1MB buffer, and we strncpy "THIS" into it using n = 1024. That's just four bytes right? Nope. strncpy() will write "THIS" and then 1020 zero bytes.
If you look at this function assuming it's a safety feature, that's a huge surprise, and indeed if you were skimming you might miss what it does because (in the context of "it's a safety feature") this is an insane choice. "Why would you do that?". Well, because it's not a safety feature.
The perf cost isn't what you'd expect from a safety feature either. Suppose we have a 1MB buffer, and we strncpy "THIS" into it using n = 1024. That's just four bytes right? Nope. strncpy() will write "THIS" and then 1020 zero bytes.