A calendar, with the dates computed rather than asked for

[ralyodio]

The second slice of #64. A month as a grid, with per-day styling: marks for days with something on, a selected day, an optional header and weekday row, and a week that starts on Monday or Sunday.

ui.calendar({
  year: 2026,
  month: 9,
  selected: 8,
  marks: [{ day: 15, color: theme.warning }],
});

No host calendar is consulted, anywhere

Every language this library is ported to has a different date type — different epochs, different month numbering, different opinions about time zones — and a widget whose output depends on any of that cannot be held to a fixture. So the arithmetic is here, in terms every port already has: integers. Sakamoto's method for the weekday, the full Gregorian leap rule, and a test that greps the TypeScript source to make sure nobody quietly reaches for Date later.

Three things that are easy to get wrong

The leap rule is the whole rule — every four years, except centuries, except every fourth century. Truncating it at "every four years" is right for 1901-2099 and wrong for 1900 and 2100, which is the kind of bug that sits quietly for decades.

The leap count divides towards negative infinity. Go, C++ and Zig all truncate towards zero by default, which is off by one for years before 1; each port uses a floor division rather than the operator.

A month is four, five or six week rows depending on where its first day falls. calendarHeight returns the month's own, and a test walks all twelve months of a year asserting that what was reserved is what got drawn — reserving five for everything leaves some months a row short and others a blank row long.

Scope

Six ports and five fixtures, all additive. The Ruby, PHP and Perl bridges gained a calendar node and COBOL a CALENDAR/CALDAY pair, which both COBOL bridges render identically. The widget gallery is now 31. This is one slice of #64; the bounds-aware canvas and Shadow are still open there, which is why this closes nothing.

Verified

• 322 TypeScript tests under both bun test and node --test, typecheck clean
• 81 widget scenes matching the reference in Rust, Go, Python, Zig and C++ (was 76)
• 11/11 ctest, ports/bindings/tests/check.py, all eleven galleries
• both COBOL bridges render the new verbs identically (diff clean)
• next build for the site

🤖 Generated with Claude Code

https://claude.ai/code/session_017Df2FNu5DhinMV2soRz3cy