FA-82812 / Chess move legality / Member archive

Enemy piece on its own king's line counted as discovered check · case 02

After a quiet white knight move, a black rook standing on its own king's file is reported as a discovered check.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

Input: {"board", "move": [from, to] or [from, to, promotion letter]}. Apply the move (promotion letter becomes a piece of the mover's colour) and classify the check it gives to the enemy king: "direct" (the moved piece attacks it), "discovered" (another of the mover's pieces now attacks it), "double" (both) or "none". Pawns attack diagonally forward, sliders need a clear path.

Why this case matters

SAN "+" suffixes and double-check rules both depend on this classification.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
defender rook on own king line	`"discovered"`	`"none"`	Failed

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