Re: Formatting `interactive' strings.

[Richard Stallman]

    This is because, for some reason, the interactive argument is handled
    using the C-level format function doprnt instead of Fformat.

The reason probably was to reduce memory use and this GC frequency.
Fformat conses a Lisp string, whereas doprnt uses a buffer provided by
the caller.

This motivation is probably obsolete now, since the space used by this
is small compared with the space Emacs conses for other purposes, and
GC is done much less often now than it was 20 years ago.

However, it would be good to check explicitly here

    !       visargs[0] = build_string (prompt1);
    !       callint_message = Fformat (i, visargs);

whether prompt1 has a %, and if not, avoid calling Fformat.

Please install your patch with that little improvement,
and thanks.