Fix have_en_passant function to prevent returning a possible en passa…

…nt in a position unreachable by the pawn

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    chess (0.3.5)
+    chess (0.3.6)
 
 GEM
   remote: http://rubygems.org/

ext/chess/special.c

@@ -170,12 +170,12 @@ update_en_passant (Board *board, int from, int to)
 int
 have_en_passant (Board *board, int from, int to)
 {
-  if (board->placement[from] == 'P' && to == board->en_passant
-      && (from == to - 7 || from == to - 9))
-    return to - 8;
-  else if (board->placement[from] == 'p' && to == board->en_passant
-      && (from == to + 7 || from == to + 9))
-    return to + 8;
+  if (board->placement[from] == 'P' && to == board->en_passant) {
+    return xray_attack_white_pawn(from) & (1ULL << to) ? to - 8 : 0;
+  }
+  if (board->placement[from] == 'p' && to == board->en_passant) {
+    return xray_attack_black_pawn(from) & (1ULL << to) ? to + 8 : 0;
+  }
   return 0;
 }
 

lib/chess/version.rb

@@ -1,5 +1,5 @@
 # The Chess library module.
 module Chess
   # The library version.
-  VERSION = '0.3.5'.freeze
+  VERSION = '0.3.6'.freeze
 end

test/test_move_generator.rb

@@ -26,4 +26,12 @@ class ChessTest < Minitest::Test
       end
     end
   end
+
+  def test_github_issue32
+    game = Chess::Game.new
+    game.moves = %w[f2f4 d7d6 d2d3 h7h5 b1d2 e7e5 f4f5 a7a5 c2c3 d8f6 d2c4 b7b6 c4d2 a8a6 d2f3 a6a7 f3e5 b6b5 h2h4]
+    generated_moves = game.board.generate_moves('a5')
+
+    assert_equal %w[a4], generated_moves
+  end
 end