Engine PR 8.3: en passant — capture generation + applyMove removal #70

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opened 2026-05-16 16:04:14 +00:00 by root · 4 comments

root commented

2026-05-16 16:04:14 +00:00

(Migrated from gitlab.core-project.space)

Imported from GitHub amaurycoudr/chess-project#70, opened by @amaurycoudr on 2026-05-16 16:04 UTC.
Closed on GitHub on 2026-05-16 21:37 UTC as completed.

Parent

#67

What to build

Additive on slice 8.1: the en passant capture. Slice 8.1 already sets the en passant target square on a double push; this slice generates the capture that consumes it and applies the board change.

Implements step 8 (partial) of docs/adr/0004-engine-slice-plan-and-king-first-piece-ordering.md.

Extend pseudoLegalPawnMoves in movegen.ts: when a side-to-move pawn attacks position.ep, generate an en passant capture move to that square (even though it is empty).
Modify applyMove in rules.ts: detect the en passant capture structurally (a pawn mover moving diagonally onto the empty position.ep square) and remove the enemy pawn from the square behind the destination — not from the destination itself.
Extend rules-pawns.test.ts with en passant coverage: capture availability only on the ply after the enabling double push, correct captured-pawn removal, en passant unavailable when no enemy pawn is positioned to take, and the en-passant-discovered-check case (an en passant capture that exposes the mover's own king is rejected by the existing legality filter).

The en-passant-discovered-check case falls out for free once applyMove removes the correct pawn — removing the captured pawn can open a rank for an enemy rook/queen onto the mover's king. It should be covered by an explicit test.

Acceptance criteria

pseudoLegalPawnMoves generates an en passant capture when a side-to-move pawn attacks position.ep
No en passant capture is generated when position.ep is undefined or no pawn attacks it
Game.apply() of an en passant capture moves the capturing pawn to ep and removes the enemy pawn from the square behind the destination
The captured-pawn removal is correct for both colors
An en passant capture that leaves the mover's king in check (en-passant-discovered-check) is excluded from legalMoves
En passant is available only on the ply immediately after the enabling double push (target cleared by any other move — already handled in 8.1, verified here)
The halfmove clock resets on an en passant capture
Tests follow the rules-knights.test.ts / rules-pawns.test.ts style, written as vertical TDD slices
pnpm lint, pnpm typecheck, pnpm test, pnpm build all green from the repo root

Blocked by

Blocked by #68

> _Imported from GitHub [amaurycoudr/chess-project#70](https://github.com/amaurycoudr/chess-project/issues/70), opened by [@amaurycoudr](https://github.com/amaurycoudr) on 2026-05-16 16:04 UTC._ > _Closed on GitHub on 2026-05-16 21:37 UTC as completed._  --- ## Parent #67 ## What to build Additive on slice 8.1: the en passant capture. Slice 8.1 already sets the en passant *target* square on a double push; this slice generates the capture that *consumes* it and applies the board change. Implements step 8 (partial) of `docs/adr/0004-engine-slice-plan-and-king-first-piece-ordering.md`. - Extend `pseudoLegalPawnMoves` in `movegen.ts`: when a side-to-move pawn attacks `position.ep`, generate an en passant capture move to that square (even though it is empty). - Modify `applyMove` in `rules.ts`: detect the en passant capture structurally (a pawn mover moving diagonally onto the empty `position.ep` square) and remove the enemy pawn from the square *behind* the destination — not from the destination itself. - Extend `rules-pawns.test.ts` with en passant coverage: capture availability only on the ply after the enabling double push, correct captured-pawn removal, en passant unavailable when no enemy pawn is positioned to take, and the en-passant-discovered-check case (an en passant capture that exposes the mover's own king is rejected by the existing legality filter). The en-passant-discovered-check case falls out for free once `applyMove` removes the correct pawn — removing the captured pawn can open a rank for an enemy rook/queen onto the mover's king. It should be covered by an explicit test. ## Acceptance criteria - [ ] `pseudoLegalPawnMoves` generates an en passant capture when a side-to-move pawn attacks `position.ep` - [ ] No en passant capture is generated when `position.ep` is undefined or no pawn attacks it - [ ] `Game.apply()` of an en passant capture moves the capturing pawn to `ep` and removes the enemy pawn from the square behind the destination - [ ] The captured-pawn removal is correct for both colors - [ ] An en passant capture that leaves the mover's king in check (en-passant-discovered-check) is excluded from `legalMoves` - [ ] En passant is available only on the ply immediately after the enabling double push (target cleared by any other move — already handled in 8.1, verified here) - [ ] The halfmove clock resets on an en passant capture - [ ] Tests follow the `rules-knights.test.ts` / `rules-pawns.test.ts` style, written as vertical TDD slices - [ ] `pnpm lint`, `pnpm typecheck`, `pnpm test`, `pnpm build` all green from the repo root ## Blocked by - Blocked by #68

root commented

2026-05-16 17:12:09 +00:00

(Migrated from gitlab.core-project.space)

Imported from a GitHub comment by @amaurycoudr on 2026-05-16 17:12 UTC.

Implemented by Sandcastle on branch sandcastle/sequential-reviewer/1778951121227 — awaiting review. Adds en passant capture generation in pseudoLegalPawnMoves and structural en passant detection in applyMove with correct captured-pawn removal.

> _Imported from a [GitHub comment](https://github.com/amaurycoudr/chess-project/issues/70#issuecomment-4467562226) by [@amaurycoudr](https://github.com/amaurycoudr) on 2026-05-16 17:12 UTC._  Implemented by Sandcastle on branch `sandcastle/sequential-reviewer/1778951121227` — awaiting review. Adds en passant capture generation in pseudoLegalPawnMoves and structural en passant detection in applyMove with correct captured-pawn removal.

root commented

2026-05-16 17:26:55 +00:00

(Migrated from gitlab.core-project.space)

Imported from a GitHub comment by @amaurycoudr on 2026-05-16 17:26 UTC.

Promoted to branch feat/engine-pr-8-1-pawns-pushes-captures-attack-mask-legality-wiring-68 (PR #72), not yet merged to main. A dependent slice should git fetch origin feat/engine-pr-8-1-pawns-pushes-captures-attack-mask-legality-wiring-68 and branch off it.

> _Imported from a [GitHub comment](https://github.com/amaurycoudr/chess-project/issues/70#issuecomment-4467607556) by [@amaurycoudr](https://github.com/amaurycoudr) on 2026-05-16 17:26 UTC._  Promoted to branch `feat/engine-pr-8-1-pawns-pushes-captures-attack-mask-legality-wiring-68` (PR #72), not yet merged to main. A dependent slice should `git fetch origin feat/engine-pr-8-1-pawns-pushes-captures-attack-mask-legality-wiring-68` and branch off it.

root (Migrated from gitlab.core-project.space) closed this issue

2026-05-16 21:37:08 +00:00

root commented

2026-10-13 08:38:30 +00:00

(Migrated from gitlab.core-project.space)

mentioned in issue #71