bug#22910: read-only setlocale has side effect

bug#22910: read-only setlocale has side effect

[Zefram]

A call to setlocale with no second argument is documented to be
a read-only operation, querying the current locale configuration.
In fact it has a side effect of setting the encoding on primordial ports:

$ guile-2.0 -c '(write (port-encoding (current-input-port))) (newline) (setlocale LC_TIME) (write (port-encoding (current-input-port))) (newline)'
#f
"ANSI_X3.4-1968"

Observe that this occurs even if the locale reading operation is for a
category unrelated to character encoding.  The actual decoding behaviour
of read-char is altered in accordance with the reported encoding.
Non-primordial ports opened before or after the setlocale call are
not affected.

-zefram

bug#22910: read-only setlocale has side effect

[Zefram]

Additional information: setlocale's side effect on primordial ports
happens even if the port's encoding has been individually set using
set-port-encoding!.  This means that to maintain a specific encoding on
these ports (other than the locale's nominal encoding, which is likely to
not be binary compatible) it is necessary to set the encoding repeatedly,
before any I/O operation after setlocale might have been called.
Since the read-only mode of setlocale has this effect, and arbitrary
library code might feel entitled to call setlocale for read purposes
without documenting that it does so, this really amounts to setting the
encoding before every I/O operation.

-zefram

bug#22910: read-only setlocale has side effect

[Andy Wingo]

On Fri 04 Mar 2016 17:48, Zefram <zefram@fysh.org> writes:

> A call to setlocale with no second argument is documented to be
> a read-only operation, querying the current locale configuration.
> In fact it has a side effect of setting the encoding on primordial ports:

This sounds like a bug indeed :/

Andy