CFTimeZone: resolve GMT offset names - #136
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CFTimeZoneCreateWithName looked for a zone file for every name, so a GMT offset such as GMT+05:00 (which has no file) returned NULL. In particular a calendar whose time zone was created from a GMT offset could not be copied back, since CFCalendarCopyTimeZone recreates the zone from its name. Parse a GMT offset name and build the zone from the offset directly.
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CFTimeZoneCreateWithName looked for a zone file for every name, so a GMT offset such as GMT+05:00 or GMT-05:00, which has no file, returned NULL. This is why CFCalendarCopyTimeZone crashed callers for a calendar whose time zone came from a GMT offset: it recreates the zone from the stored name, got NULL back, and an unguarded caller then dereferenced it.
Parse a GMT offset name (GMT followed by a sign and the hours and minutes, with or without a colon) and build the zone from the offset directly, the same way CFTimeZoneCreateWithTimeIntervalFromGMT does. Plain named zones such as GMT and UTC still resolve through their zone files as before.
Tests/CFTimeZone/gmt.m checks the GMT, UTC and GMT-05:00 offsets and the CFCalendarCopyTimeZone round-trip, verified against Apple CoreFoundation.