Re: Test failures in --disable-multibyte

[Peter Stephenson <p.w.stephenson@xxxxxxxxxxxx>]

On Wed, 2020-01-01 at 13:44 +0000, Daniel Shahaf wrote:
> > It's not generally expected you'll want to disable multibyte explicitly,
> > but it tests the case you get if you have a system which doesn't have
> > the required multibyte support.  It's not clear if zsh gets compiled on
> > such systems now --- they won't be very common but there might be some
> > deliberately reduced systems for low-level use.  These only need testing
> > in a similarly limited fashion.
> 
> This state of affairs doesn't sound quite right.  If those codepaths
> need testing, the test suite should be made to pass in that
> configuration, so that bugfixes would be able to be tested for
> unintended side effects.  With no working test suite and no known
> users, it sounds like --disable-multibyte is _de facto_ unsupported,
> but we are not ready to officially pull the plug on it due to the
> possibility of it being used on a C99-less embedded system somewhere.
> So, how about having NEWS in 5.8 say that unless someone asks us to
> continue supporting --disable-multibyte, it will become unsupported
> and may be removed?

You're correct, it's de facto unsupported.  The difference is largely
whether anyone gets around to fixing it, which is hard to predict --- I
don't think the problems are likely to be hard.  So certainly it would
be useful to get interest.  Alas, experience suggests most people don't
take much notice until the point where it actually stops working for
them.  So as long as we point out there are problems, I think whatever
takes the least number of hostages to fortune is probably the right
thing to say.

With the changes being largely minor and even cosmetic (but they're
certainly not all cosmetic) it probably doesn't make sense to remove
it any time soon.  But it could rot further, so possibly a warning is
sensible.

Of course, the best solution would be someone relying on simple
character handling taking it over themselves.

> (For what it's worth, even on embedded systems it should be trivial to
> implement the requisite standard library functions¹ for the ASCII-only
> subset of inputs in terms of the C89 standard library, which we
> already require.)

This is pure guesswork, so if you have a solid estimate of how much work
that is you're ahead of me, but I'd be surprised if this was easier in
practice than fixing up the simple mode directly, although it is more
future-proof.

pws