Add COUP* coupon date functions#74
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Implements COUPDAYBS, COUPDAYS, COUPDAYSNC, COUPNCD, COUPNUM and COUPPCD with shared date/basis helpers, wires them into dispatch and static analysis, adds parser fallbacks, tests, and docs.
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| fn is_leap_year(year: i32) -> bool { | ||
| (year % 4 == 0) && (year % 100 != 0 || year % 400 == 0) | ||
| } |
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Duplicated is_leap_year function across modules
Low Severity
The is_leap_year function in financial.rs is identical to the existing one in date_and_time.rs. Both implementations have the same signature fn is_leap_year(year: i32) -> bool and the same logic (year % 4 == 0) && (year % 100 != 0 || year % 400 == 0). This is redundant code that increases maintenance burden - if a bug were found in this logic, it would need to be fixed in both places.
| // Rule 1: If both date A and B fall on the last day of February, then date B will be changed to the 30th | ||
| if is_last_day_of_february(start) && is_last_day_of_february(end) { | ||
| d2 = DAYS_IN_MONTH_360; | ||
| } |
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US 30/360 February rule differs from existing implementation
High Severity
The days360_us function's Rule 1 only adjusts end date to 30 when BOTH dates are the last day of February. However, the existing fn_days360 adjusts end date to 30 when end is last day of February AND start day became 30 (from being 31st OR Feb last day). This causes inconsistent results: for dates like March 31 to Feb 28, fn_days360 returns 690 but days360_us returns 688. COUPDAYBS and COUPDAYSNC with basis=0 will produce different results than DAYS360 for the same date ranges.
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Summary
Test plan
cargo test --package ironcalc_base couponNote
Medium Risk
Adds new date/day-count financial computations (including 30/360 US/EU February edge-case rules), which can subtly affect numeric results and error behavior for workbook evaluations.
Overview
Adds support for Excel coupon-date functions
COUPDAYBS,COUPDAYS,COUPDAYSNC,COUPNCD,COUPNUM, andCOUPPCD, including shared helpers for coupon period selection and day-count conventions (30/360 US/EU and actual).Wires the new functions through parsing (including
_xlfn.fallback), function dispatch/name mapping, and static analysis signatures/return types. Includes a newtest_fn_couponsuite covering happy paths, argument validation, an actual-day-count vs fixed-day-countCOUPDAYSfix, and February/leap-year edge cases; docs are updated to mark these functions as available and link to stub pages.Written by Cursor Bugbot for commit 23fffdf. Configure here.