Branch: refs/heads/smoke-me/khw-strftime
Home: https://github.com/Perl/perl5
Commit: 5e0ef8d56f5f069433941408b2900eb485a5c1da
https://github.com/Perl/perl5/commit/5e0ef8d56f5f069433941408b2900eb485a5c1da
Author: Karl Williamson <[email protected]>
Date: 2025-11-20 (Thu, 20 Nov 2025)
Changed paths:
M ext/POSIX/t/posix.t
Log Message:
-----------
posix.t: Properly populate optional fields to strtime
The next commits that fix some bugs showed these were not properly
getting initialized.
Commit: 9688a1f2c2803c8e0bf7fc9bd175b56a74079584
https://github.com/Perl/perl5/commit/9688a1f2c2803c8e0bf7fc9bd175b56a74079584
Author: Karl Williamson <[email protected]>
Date: 2025-11-20 (Thu, 20 Nov 2025)
Changed paths:
M locale.c
Log Message:
-----------
locale.c: Silence unused variable compiler warning
On some systems this was unused. Now that we have C99, we can move the
declaration and some #ifdef's and not declare it unless it is going to
be used.
Commit: ee2fa93c90df714c339f28acb2a24a25ca80915f
https://github.com/Perl/perl5/commit/ee2fa93c90df714c339f28acb2a24a25ca80915f
Author: Karl Williamson <[email protected]>
Date: 2025-11-20 (Thu, 20 Nov 2025)
Changed paths:
M locale.c
Log Message:
-----------
locale.c: Slight comment clarification
Commit: b1b276939d1d013002cda91b9e3f9f8c2968bf33
https://github.com/Perl/perl5/commit/b1b276939d1d013002cda91b9e3f9f8c2968bf33
Author: Karl Williamson <[email protected]>
Date: 2025-11-20 (Thu, 20 Nov 2025)
Changed paths:
M locale.c
Log Message:
-----------
locale.c: ints_to_tm: Fix #if's
tl;dr:
Fixes GH #23878
I botched this in Perl 5.42. These conditional compilation statements
were just plain wrong, causing code to be skipped that should have been
compiled. It only affected the few hours of the year when daylight
savings time is removed, so that the hour value is repeated. We didn't
have a good test for that.
gory details:
libc uses 'struct tm' to hold information about a given instant in
time, containing fields for things like the year, month, hour, etc. The
libc function mktime() is used to normalize the structure, adjusting,
say, an input Nov 31 to be Dec 01.
One of the fields in the structure, 'is_dst', indicates if daylight
savings is in effect, or whether that fact is unknown. If unknown,
mktime() is supposed to calculate the answer and to change 'is_dst'
accordingly. Some implementations appear to always do this calculation
even when the input value says the result is known. Others appear to
honor it.
Some libc implementations have extra fields in 'struct tm'.
Perl has a stripped down version of mktime(), called mini_mktime(),
written by Larry Wall a long time ago. I don't know why. This crippled
version ignores locale and daylight time. It also doesn't know about
the extra fields in 'struct tm' that some implementations have. Nor can
it be extended to know about those fields, as they are dependent on
timezone and daylight time, which it deliberately doesn't consider.
The botched #ifdef's were supposed to compensate for both the extra
fields in the struct and that some libc implementations always
recalculate 'is_dst'.
On systems with these fields, the botched #if's caused only
mini_mktime() to be called. This meant that these extra fields didn't
get populated, and daylight time is never considered to be in effect.
And 'is_dst' does not get changed from the input.
On systems without these fields, the regular libc mktime() would be
called appropriately.
The bottom line is that for the portion of the year when daylight
savings is not in effect, that portion worked properly. The two extra
fields would not be populated, so if some code were to read them, it
would only get the proper values by chance. We got no reports of this.
I attribute that to the fact that the use of these is not portable, so
code wouldn't tend to use them. There are portable ways to access the
information they contain.
Tests were failing for the portions of the year when daylight savings is
in effect; see GH #22351. The code looked correct just reading it (not
seeing the flaw in the #ifdef's), so I assumed that it was an issue in
the libc implementations and instituted a workaround. (I can't now
think of a platform where there hasn't been a problem with a libc with
something regarding locales, so that was a reasonable assumption.)
Among other things (fixed in the next commit), that workaround overrode
the 'is_dst' field after the call to mini_mktime(), so that the value
actually passed to libc strftime() indicated that daylight is in effect.
What happens next depends on the libc strftime() implementation. It
could conceivably itself call mktime() which might choose to override
is_dst to be the correct value, and everything would always work. The
more likely possibility is that it just takes the values in the struct
as-is. Remember that those values on systems with the extra fields were
calculated as if daylight savings wasn't in effect, but now we're
telling strftime() to use those values as if it were in effect. This
is a discrepancy. I'd have to trace through some libc implementations
to understand why this discrepancy seems to not matter except at the
transition time.
But the bottom line is this commit removes that discrepancy, and causes
mktime() to be called appropriately on systems where it wasn't, so
strftime() should now function properly.
Commit: 4e2b932ac89641e33f108986b05eb2dcf910534e
https://github.com/Perl/perl5/commit/4e2b932ac89641e33f108986b05eb2dcf910534e
Author: Karl Williamson <[email protected]>
Date: 2025-11-20 (Thu, 20 Nov 2025)
Changed paths:
M locale.c
Log Message:
-----------
my_strftime(): Properly take daylight savings into account
Because of the bug fixed in the previous commit, this function was
changed in 5.42 to have a work around, which is no longer needed.
Commit: 62a236ecb65a53af79b8971c4f83ed0eb2c8b090
https://github.com/Perl/perl5/commit/62a236ecb65a53af79b8971c4f83ed0eb2c8b090
Author: Karl Williamson <[email protected]>
Date: 2025-11-20 (Thu, 20 Nov 2025)
Changed paths:
M ext/POSIX/POSIX.xs
M ext/POSIX/lib/POSIX.pm
Log Message:
-----------
POSIX.xs: Properly take daylight savings into account
Because of the bug fixed two commits ago, this function was changed in
5.42 to have a work around, which is no longer needed.
Commit: 2da6a35167b8bae39abecefd494524d13a4ee932
https://github.com/Perl/perl5/commit/2da6a35167b8bae39abecefd494524d13a4ee932
Author: Karl Williamson <[email protected]>
Date: 2025-11-20 (Thu, 20 Nov 2025)
Changed paths:
M ext/POSIX/t/time.t
Log Message:
-----------
POSIX/t/time.t: Add tests for DST changes
Commit: 1ecf83e2750b10fdc05631bfbe497dbe3382ade9
https://github.com/Perl/perl5/commit/1ecf83e2750b10fdc05631bfbe497dbe3382ade9
Author: Karl Williamson <[email protected]>
Date: 2025-11-20 (Thu, 20 Nov 2025)
Changed paths:
M ext/POSIX/lib/POSIX.pod
M locale.c
Log Message:
-----------
perlapi: Add extensive strftime documentation
Due to the differences in various systems' implementations, I think it
is a good idea to more fully document the vagaries I have discovered,
and how perl resolves them.
Commit: a508c3ca00586ce06a3bac73f5a21af9d1b6300a
https://github.com/Perl/perl5/commit/a508c3ca00586ce06a3bac73f5a21af9d1b6300a
Author: Karl Williamson <[email protected]>
Date: 2025-11-20 (Thu, 20 Nov 2025)
Changed paths:
M pod/perldelta.pod
Log Message:
-----------
perldelta for GH #23878
Commit: 2036d412875cf6e33ba4e44b1bf8ee6f1345fe05
https://github.com/Perl/perl5/commit/2036d412875cf6e33ba4e44b1bf8ee6f1345fe05
Author: Karl Williamson <[email protected]>
Date: 2025-11-20 (Thu, 20 Nov 2025)
Changed paths:
M ext/POSIX/t/time.t
Log Message:
-----------
tzset
Commit: 2cc250780461298c528c03aeae0669fd79f98176
https://github.com/Perl/perl5/commit/2cc250780461298c528c03aeae0669fd79f98176
Author: Karl Williamson <[email protected]>
Date: 2025-11-20 (Thu, 20 Nov 2025)
Changed paths:
M ext/POSIX/t/time.t
Log Message:
-----------
trial2
Compare: https://github.com/Perl/perl5/compare/5db16171530a...2cc250780461
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