Excel's EDATE and EOMONTH read serial 0 as 0 January 1900 and end
February 1900 on the 28th (serial 59), although the sheet itself keeps
the Lotus 29 February 1900 (serial 60). GridCraft clamped day 0 up to
day 1 and used the sheet's 29-day February, so EDATE(0,0) was 1,
EDATE(0,1) 32, EDATE(31,1) and EOMONTH(59,0) 60.
EDATE now keeps day 0 and both functions take the real calendar's month
lengths. Serial 60 still reads as 29 February, so EDATE(60,1) stays
29 March. DATE, DAY and the parser keep the leap day.
Tests: the Excel 365 table from the issue; the #124 cases that expected
60 at the end of February 1900 now expect 59.
Restores "Counts whole years, months or days between two dates." and
appends the units, in the multi-line form rustfmt gives a long entry.
Drops the 256-argument test case: the parser already refuses more than
255 arguments, so it never reached the entry check. (993c108's message
says entry "also refuses" them; it already did.)
Claude-Session: https://claude.ai/code/session_01BGBBGBC2gRpQ7GDuwQ6WPt
A formula calling a built-in function with too few or too many
arguments (=DATEDIF(a,b), =SUM(), =DATE(2024,1)) was stored and showed
#VALUE! with no hint about what was wrong. Entry now refuses it with
the function's signature, e.g. "DATEDIF has too few arguments. Use
DATEDIF(start_date, end_date, unit)", and leaves the cell unchanged.
Only registered functions are checked: special forms the evaluator
handles itself (IF, LET, LAMBDA...), LAMBDA names and unknown functions
are skipped. Paste and Find & Replace keep turning input that fails
entry into text. DATEDIF's description now lists its units.
Fixes#363
Claude-Session: https://claude.ai/code/session_01BGBBGBC2gRpQ7GDuwQ6WPt
serial_from_ymd worked out the real calendar date and then moved serials
up to 60 down by one. February 1900 has no 29th in the real calendar, so
DATE(1900,2,29) and DATEVALUE("2/29/1900") rolled over to 1 March (61),
and DATE(1900,3,0) gave 28 February (59). Excel's 1900 system keeps the
Lotus leap day: serial 60 is 29 February 1900, and DAY(60) already
said so.
The serial of the first of the month is now taken in Excel's calendar
(one lower up to February 1900), and the day, with any overflow, counts
on from there. So day and month overflow pass through serial 60 both
ways: DATE(1900,1,60), DATE(1900,4,-31) and DATE(1901,-10,29) are 60 too.
Month and day arithmetic is checked, so hostile values return None.
days_in_month_in gives February 1900 29 days in the 1900 system; EDATE
and EOMONTH use it, so EOMONTH(60,0) is 60 rather than the day before,
and the text parser uses it in place of its own special case. The 1904
system is unchanged (1900 is before its epoch).
Tests: serials around the leap day (overflow both ways, every serial
0-366 round-trips through its year, month and day), hostile months and
days, parsing 2/29/1900 and 1900-02-29, DATE/DATEVALUE/EDATE/EOMONTH
in the 1900 system and the 1904 system. The DATE, DATEVALUE and serial
cases fail before the fix.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Marco Arnulfo