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Previously the libc path in init_timezone() was gated on HAVE_DECL_TZNAME, which configure only defines when struct tm lacks tm_zone. On Linux and macOS this meant timezone, altzone, daylight and tzname were guessed by sampling localtime() near January 1 and July 1 of the current year. That gives stale values when a zone's rules change mid-year (e.g. America/Vancouver moving to permanent MST on 2026-11-01) and wrong standard/DST names for negative DST zones. Add a configure check, HAVE_TIMEZONE_GLOBALS, that verifies timezone, daylight and tzname are usable as variables, and use libc's values whenever it is defined. FreeBSD, where timezone is a function, keeps the sampling fallback. When libc has no altzone, use timezone - 3600 only if daylight is set, otherwise timezone.
nascheme
marked this pull request as ready for review
November 5, 2026 02:58
nascheme
requested review from
a team,
AA-Turner,
StanFromIreland,
corona10,
emmatyping,
erlend-aasland,
itamaro and
pganssle
as code owners
November 5, 2026 02:58
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Previously the libc path in init_timezone() was gated on HAVE_DECL_TZNAME, which configure only defines when struct tm lacks tm_zone. On Linux and macOS this meant timezone, altzone, daylight and tzname were guessed by sampling localtime() near January 1 and July 1 of the current year. That gives stale values when a zone's rules change mid-year (e.g. America/Vancouver moving to permanent MST on 2026-11-01) and wrong standard/DST names for negative DST zones.
Add a configure check, HAVE_TIMEZONE_GLOBALS, that verifies timezone, daylight and tzname are usable as variables, and use libc's values whenever it is defined. FreeBSD, where timezone is a function, keeps the sampling fallback. When libc has no altzone, use timezone - 3600 only if daylight is set, otherwise timezone.
Note: creation of this PR was assisted by an LLM.