RTL: month and day name arrays

• Type: feature (library / RTL date formatting) — Track B
• Status: done
• Opened: 2026-07-26 — found while wiring [[feature-lib-regex-engine]] into make lib-test: the target is ALREADY red before that change, and the red was not ticketed.

The red

$(PXX_STABLE) --mimic-fpc -Fuexternal/synapse -Fulib/rtl -Fulib/rtl/platform/posix \
    test/lib_synapse.pas /tmp/lib_synapse
pascal26:4422: error: undefined variable (ShortMonthNames)
  near: CustomMonthNames n ShortMonthNames >>> n

Reproduced on a clean tree (git stash -u + make lib-test), so it predates the regex work. grep -rn ShortMonthNames lib/rtl/*.pas finds nothing: the RTL simply has no month-name table.

Shape

FPC exposes these as writable arrays in sysutils, which is what Synapse's date formatting reaches for:

• ShortMonthNames: array[1..12] of string ('Jan'..'Dec')
• LongMonthNames: array[1..12] of string ('January'..'December')
• ShortDayNames: array[1..7] of string, LongDayNames: array[1..7] of string

Writable, because code overrides them for locale-independent output — Synapse assigns through CustomMonthNames. Whether they live in sysutils next to the existing date helpers or in dateutils is the implementer's call; --mimic-fpc callers expect the sysutils spelling.

Gate

make lib-test reaches and passes the lib_synapse step (Track B: build with $(PXX_STABLE), never rebuild the compiler).

RESOLVED — verified 2026-07-31

lib/rtl/sysutils.pas declares all four arrays as writable module variables (ShortMonthNames / LongMonthNames / ShortDayNames / LongDayNames) and initialises them to the English table, which is what Synapse's CustomMonthNames copies out of. test/lib_synapse.pas compiles with --mimic-fpc and passes; the step is asserted in lib-test and the gate is green.

Log

• 2026-07-31 — resolved, commit 2c9dc2317.