Re: tzset: add native Windows workaround

[Paul Eggert]

On 05/01/2017 09:40 AM, Bruno Haible wrote:
> +  /* If the environment variable TZ has been set by Cygwin, neutralize it.
> +     The Microsoft CRT interprets TZ differently than Cygwin and produces
> +     incorrect results if TZ has the syntax used by Cygwin.  */
> +  const char *tz = getenv ("TZ");
> +  if (tz != NULL && strchr (tz, '/') != NULL)
> +    _putenv ("TZ=");

I'm puzzled why setting TZ="" is desirable here. Does this cause the 
Microsoft CRT to use UTC? Is TZ="" a good thing because switching to UTC 
is better than the undefined behavior one would get with TZ set to a 
value not documented by Microsoft? If so, perhaps a comment to that 
effect would help.

Also, the test "strchr (tz, '/') != NULL" allows many Cygwin-compatible 
TZ settings that Microsoft does not document support for, e.g., 
TZ="PST8PDT,M3.2.0,M11.1.0" for Los Angeles. Admittedly most Cygwin 
users in L.A. probably just use TZ="America/Los_Angeles" so fixing this 
is not that important. Still, if the intent is to limit the TZ value to 
what Microsoft documents, I suppose you could nuke the TZ value if it 
does not match the C-locale ERE 
"^[A-Za-z]{3}[-+]?[01]?[0-9](:[0-5][0-9](:[0-5][0-9])?)?([A-Za-z]{3})?$", 
or maybe put in a FIXME comment to that effect.