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date: named-timezone support on wasm32-unknown-unknown — verify, then keep or gate #225

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@tobert

Found while measuring the try-kaish wasm binary for size (kaish-extras): the shipped browser build contains zero timezone-name strings — LTO/DCE appears to eliminate chrono-tz's name table entirely. If that's right, date's named-zone path (chrono_tz::Tz lookups) cannot succeed in the browser build even though the code path exists.

Worth a quick verify on wasm32-unknown-unknown (the kaish-extras playground makes this easy), then a decision:

  • keep: ensure the table survives in wasm builds (costs bundle size — the wire cost of the full table is roughly 150–250 KB gzipped), or
  • gate: put chrono-tz behind a tz-database feature (default-on native, off for browser embedders) with a loud "named timezones unavailable in this build" error — the core-deps-lightening move, matching how --host degrades in non-native builds.

UTC/Local/fixed-offset rendering works today in the browser (chrono wasmbind landed in #205); this is only about named zones. Size work is otherwise waved off — this survives as a correctness question.

🤖 Generated with Claude Code

https://claude.ai/code/session_017iutoShYRUYwdv94ZwBmPj

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