io_error_code was private, so the predicates built on it (is_halt,
is_skippable_title_stub, is_disc_level_no_key) were the only way to ask
anything about an io::Error's origin. A consumer that needs the code
itself — to report WHY a title failed rather than to branch on one of
three known cases — had no route to it: mux_stream returns an io::Error,
the typed Error is gone by then, and only the E<code> string prefix
survives.
That left every front-end to re-implement the prefix parse by hand,
which is precisely the string-matching 1.5.x spent its time removing.
One parser, exported.
No behaviour change: the function is unchanged and the three predicates
still call it.
Matthew Jackson
d50a7173ad