NowChessSystems/docs/unresolved.md

[2026-03-31] Unreachable code blocking 100% statement coverage

Requirement/Bug: Reach 100% statement coverage in core module.

Root Cause: 4 remaining uncovered statements (99.6% coverage) are unreachable code:

1. PgnParser.scala:160 (case _ => None in extractPromotion) - Regex =([QRBN]) only matches those 4 characters; fallback case can never execute
2. GameHistory.scala:29 (addMove$default$4 compiler-generated method) - Method overload 3 without defaults shadows the 4-param version, making promotionPiece default accessor unreachable
3. GameEngine.scala:201-202 (case _ in completePromotion) - GameController.completePromotion always returns one of 4 expected MoveResult types; catch-all is defensive code

Attempted Fixes:

1. Added comprehensive PGN parsing tests (all 4 promotion types) - PgnParser improved from 95.8% to 99.4%
2. Added GameHistory tests using named parameters - hit addMove$default$3 (castleSide) but not $default$4 (promotionPiece)
3. Named parameter approach: addMove(from=..., to=..., promotionPiece=...) triggers 4-param with castleSide default ✓
4. Positional approach: addMove(f, t, None, None) requires all 4 args (explicit, no defaults used) - doesn't hit $default$4
5. Root issue: Scala's overload resolution prefers more-specific non-default overloads (2-param, 3-param) over the 4-param with defaults

Recommendation: 99.6% (1029/1033) is maximum achievable without refactoring method overloads. Unreachable code design patterns:

• Pattern 1 (unreachable regex fallback): Defensive pattern match against exhaustive regex
• Pattern 2 (overshadowed defaults): Method overloads shadow default parameters in parent signature
• Pattern 3 (defensive catch-all): Error handling for impossible external API returns