From bc0422a53ef106a60ff7a93d463a494e3be1b8cd Mon Sep 17 00:00:00 2001
From: Paul-Nicolas Madelaine <pnm@pnm.tf>
Date: Thu, 18 Dec 2025 00:04:41 +0100
Subject: [PATCH] wip: update MoveGen

---
 src/moves.rs    | 12 +++++-------
 src/position.rs | 39 ++++++++++++++++++++++-----------------
 2 files changed, 27 insertions(+), 24 deletions(-)

diff --git a/src/moves.rs b/src/moves.rs
index 335b734..0567d5c 100644
--- a/src/moves.rs
+++ b/src/moves.rs
@@ -223,17 +223,15 @@ pub struct Moves<'l> {
 
 impl<'l> MoveGen<Infallible> for Moves<'l> {
     #[inline]
-    fn is_check(&mut self) -> ControlFlow<Infallible> {
-        self.is_check = true;
-        ControlFlow::Continue(())
-    }
-    #[inline]
-    fn en_passant_is_legal(&mut self) -> ControlFlow<Infallible> {
-        self.en_passant_is_legal = true;
+    fn checkers(&mut self, b: Bitboard) -> ControlFlow<Infallible> {
+        self.is_check = !b.is_empty();
         ControlFlow::Continue(())
     }
     #[inline]
     fn extend(&mut self, s: MoveSet) -> ControlFlow<Infallible> {
+        if let MoveSet::EnPassant { .. } = s {
+            self.en_passant_is_legal = true;
+        }
         s.for_each(|raw| unsafe { self.array.push_unchecked(raw) });
         ControlFlow::Continue(())
     }
diff --git a/src/position.rs b/src/position.rs
index f6a3f64..9967257 100644
--- a/src/position.rs
+++ b/src/position.rs
@@ -130,8 +130,10 @@ impl Position {
     /// Returns `true` if the king is in check.
     #[must_use]
     pub fn is_check(&self) -> bool {
-        struct MoveGenImpl;
-        impl MoveGen<()> for MoveGenImpl {
+        struct MoveGenImpl {
+            checkers: Bitboard,
+        }
+        impl MoveGen<core::convert::Infallible> for MoveGenImpl {
             #[inline]
             fn roles(&self, _role: Role) -> bool {
                 false
@@ -145,11 +147,16 @@ impl Position {
                 Bitboard::new()
             }
             #[inline]
-            fn is_check(&mut self) -> ControlFlow<()> {
-                ControlFlow::Break(())
+            fn checkers(&mut self, b: Bitboard) -> ControlFlow<core::convert::Infallible> {
+                self.checkers = b;
+                ControlFlow::Continue(())
             }
         }
-        self.generate_moves(&mut MoveGenImpl).is_break()
+        let mut acc = MoveGenImpl {
+            checkers: Bitboard::new(),
+        };
+        let ControlFlow::Continue(()) = self.generate_moves(&mut acc);
+        !acc.checkers.is_empty()
     }
 
     /// Returns `true` if there is no legal move on the position.
@@ -184,8 +191,11 @@ impl Position {
                 self.to
             }
             #[inline]
-            fn en_passant_is_legal(&mut self) -> ControlFlow<()> {
-                ControlFlow::Break(())
+            fn extend(&mut self, s: MoveSet) -> ControlFlow<()> {
+                match s {
+                    MoveSet::EnPassant { .. } => ControlFlow::Break(()),
+                    _ => ControlFlow::Continue(()),
+                }
             }
         }
         let mut moves = MoveGenImpl {
@@ -761,11 +771,7 @@ pub(crate) trait MoveGen<S> {
     }
 
     #[inline]
-    fn is_check(&mut self) -> ControlFlow<S> {
-        ControlFlow::Continue(())
-    }
-    #[inline]
-    fn en_passant_is_legal(&mut self) -> ControlFlow<S> {
+    fn checkers(&mut self, _b: Bitboard) -> ControlFlow<S> {
         ControlFlow::Continue(())
     }
     #[inline]
@@ -829,6 +835,8 @@ impl Position {
             | x & theirs.bishop()
             | y & theirs.rook();
 
+        moves.checkers(checkers)?;
+
         if moves.roles(Role::King) && global_mask_from.contains(king_square) {
             let attacked = {
                 let blockers = blockers ^ ours.king();
@@ -887,7 +895,6 @@ impl Position {
         }
 
         if checkers.len() > 1 {
-            moves.is_check()?;
             return ControlFlow::Continue(());
         }
 
@@ -971,7 +978,6 @@ impl Position {
                             & candidates
                             & (!pinned | lookup::segment(king_square, to))
                         {
-                            moves.en_passant_is_legal()?;
                             moves.extend(MoveSet::EnPassant { from, to })?;
                         }
                     }
@@ -1006,7 +1012,6 @@ impl Position {
         }
 
         if checker.is_some() {
-            moves.is_check()?;
             return ControlFlow::Continue(());
         }
 
@@ -1233,8 +1238,8 @@ impl MateMoveGenImpl {
 }
 impl MoveGen<Infallible> for MateMoveGenImpl {
     #[inline]
-    fn is_check(&mut self) -> ControlFlow<Infallible> {
-        self.is_check = true;
+    fn checkers(&mut self, b: Bitboard) -> ControlFlow<Infallible> {
+        self.is_check = !b.is_empty();
         ControlFlow::Continue(())
     }
     #[inline]