[PATCH] filter: set environment variable PYTHONIOENCODING to utf-8

[john at keeping.me.uk (John Keeping)]

On Fri, Mar 17, 2017 at 07:07:02PM +0100, Jason A. Donenfeld wrote:
> On Sun, Mar 12, 2017 at 6:51 PM, John Keeping <john at keeping.me.uk> wrote:
> > While I'm inclined to agree with this, in this particular case we
> > explicitly encode pages as UTF-8 so there is an argument that we should
> > be telling child processes that UTF-8 is the correct encoding.
> 
> That's a compelling argument, actually.
> 
> >
> > Maybe we should be looking to change LANG instead, but I'm not sure how
> > reliably we can do that.
> 
> I'm more onboard with that. Does changing LANG influence the PYTHON
> variable implicitly?

Yes, if there is no explicit encoding requested then Python derives it
from the locale.

However, it only works if the locale actually exists on the system; for
example on my system I get:

$ LANG=en_GB.UTF-8 python2 -c 'import sys; print(sys.stdin.encoding)'
UTF-8
$ LANG=en_GB.ISO-8859-1 python2 -c 'import sys; print(sys.stdin.encoding)' 
ISO-8859-1

but I don't have C.UTF-8, so:

$ LC_ALL=C.UTF-8 python2 -c 'import sys; print(sys.stdin.encoding)'
ANSI_X3.4-1968

There's an open glibc bug [1] to support C.UTF-8 but for now it looks
like it's only available on Debian and derivatives.

> > Is it safe to do something like:
> >
> >         const char *lang = getenv("LANG");
> >         struct strbuf sb = STRBUF_INIT;
> >
> >         if (!lang)
> >                 lang = "C";
> >         strbuf_addf(&sb, "%.*s.UTF-8",
> >                     (int) (strchrnul(lang, '.') - lang), lang);
> >         setenv("LANG", sb.buf);
> 
> That's probably not too bad, though I wonder if we could get away with
> just explicitly setting a more generic UTF-8 instead of trying to read
> the user's language preferences.

Other people have already found that it's not quite that simple [2] if
we want it to work on all systems.

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=17318
[2] https://github.com/commercialhaskell/stack/issues/856