Revert "Remove `checked_add` in `Layout::repeat`" This fixes a a segfault in safe code, a stable regression. Reported in #69225. This reverts commit a983e0590a43ed8b0f60417828efd4e79b51f494.
char::is_ascii_*
checked_add
Layout::repeat
repr(no_niche)
UnsafeCell
Self
rustc_on_unimplemented