date,touch: allow timezone offsets in dates

Allow ISO 8601 style dates to include a timezone offset.  Like
the '@' format these dates aren't relative to the user's current
timezone and shouldn't be subject to DST adjustment.

- The implementation uses the strptime() '%z' format specifier.
  This an extension which may not be available so the use of
  timezones is a configuration option.

- The 'touch' applet has been updated to respect whether DST
  adjustment is required, matching 'date'.

function                                             old     new   delta
parse_datestr                                        624     730    +106
static.fmt_str                                       106     136     +30
touch_main                                           388     392      +4
date_main                                            818     819      +1
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 4/0 up/down: 141/0)             Total: 141 bytes

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/libbb/Config.src b/libbb/Config.src
index f97de8ef7..58c5fad50 100644
--- a/libbb/Config.src
+++ b/libbb/Config.src
@@ -395,3 +395,14 @@ config FEATURE_HWIB
         default y
         help
         Support for printing infiniband addresses in network applets.
+
+config FEATURE_TIMEZONE
+        bool "Allow timezone in dates"
+        default y
+        depends on DESKTOP
+        help
+        Permit the use of timezones when parsing user-provided data
+        strings, e.g. '1996-04-09 12:45:00 -0500'.
+
+        This requires support for the '%z' extension to strptime() which
+        may not be available in all implementations.