fix(date-fns): format() returns formatted string (was undefined)#993
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Wires the missing NATIVE_MODULE_TABLE rows for `date-fns` so the
manifest's `method("date-fns", "format", false, _)` actually reaches
`js_datefns_format` at codegen, and rewrites the runtime impl to handle
date-fns's lowercase LDML tokens (`yyyy/MM/dd`) in local time instead of
delegating to the dayjs formatter (which only understands uppercase
tokens and formats in UTC).
proggeramlug
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May 18, 2026
PR #993 only emitted runs of repeated letters, so date-fns ordinal tokens like `do` were split into a `d` run ("6") and a lone `o` which fell into the unknown-letter catch-all ("o") — producing "January 6o 2020" instead of "January 6th 2020". Extends the token loop to: - Detect single-letter run + literal `o` over the date-fns ordinal alphabet ([yYQqMLwIdDecihHKkms]o) and emit an English ordinal via a new `english_ordinal()` helper (handles 11/12/13 → "th"). - Differentiate AM/PM by run length: a/aa = AM/PM, aaa = am/pm, aaaa = a.m./p.m., aaaaa = a/p. Test fixture extended to cover yyyy-MM-dd HH:mm:ss, MMMM do yyyy, EEEE, do/Mo/yo, and the four a-variants — all match `node --experimental-strip-types` on date-fns@4.1.0 byte-for-byte.
This was referenced May 18, 2026
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Summary
import { format } from 'date-fns'; format(new Date(2020, 0, 6), 'yyyy-MM-dd')was compiling and running cleanly but printingundefined. The manifest declaredmethod("date-fns", "format", ...)butNATIVE_MODULE_TABLEinlower_call.rshad nomodule: "date-fns"rows, sonative_module_lookupreturnedNoneand the call fell through to the unknown-native branch.format,parseISO,addDays/Months/Years,differenceInDays/Hours/Minutes,isAfter/Before,startOfDay/endOfDay). Allhas_receiver: falsesince date-fns is a functional API.js_datefns_formatto handle date-fns's lowercase Unicode-LDML tokens (yyyy/MM/dd/HH/mm/ss/...) and format inchrono::Localso the day-of-month matches Node on a non-UTC machine. The prior implementation reusedjs_dayjs_format, which only recognises uppercaseYYYY/DDand formats in UTC — wrong on both counts for date-fns.Test plan
format(new Date(2020, 0, 6), 'yyyy-MM-dd')now prints2020-01-06(matched byte-for-byte againstnode --experimental-strip-types).format(d, 'yyyy'),format(d, 'MM'),format(d, 'dd'),typeof format(d, 'yyyy')all match Node output.test-files/test_date_fns_format.tsextended with end-to-endformat(...)checks alongside the existing regex-token regression cases; existing regex output unchanged.cargo build --release -p perry-runtime -p perry-stdlib -p perry-jsruntime -p perryclean.