@brson Do you have a link for this discussion?
For my use case, the panics in libcore are at least as important as the compiler-generated ones. I'd also prefer to keep the file/line info and discard the format -- presumably the 1-argument lang item call keeps the format? Discarding all the arguments would be acceptable, but suboptimal.
I feel like there should be some way to optimize an option-less format argument to use simpler (and faster) versions of Formatter::{pad, pad_integral}. Maybe it requires changing the formatter traits. I'll experiment with it.