Fix bug in AI handling of blank letters

src/board.rs

@@ -100,6 +100,10 @@ impl Letter {
         }
     }
 
+    pub fn partial_match(&self, other: &Letter) -> bool {
+        self == other || (self.is_blank == other.is_blank && self.points == other.points)
+    }
+
 }
 
 #[derive(Debug, Copy, Clone, Serialize)]

src/player_interaction/ai.rs

@@ -376,8 +376,6 @@ impl AI {
 
     ) {
 
-        assert!(!letter.is_blank); // we should have handled blanks in evaluate_letter_at_spot
-
         // let's now assign the letter to this spot
         let mut line_letters = line_letters.clone();
         *line_letters.get_mut(line_index as usize).unwrap() = Some(letter);
@@ -476,13 +474,15 @@ impl AI {
 
         available_letters.iter()
             .for_each(|in_tray| {
-                if skipped_one || *in_tray != letter {
+                if skipped_one || !in_tray.partial_match(&letter) {
                     new_available_letters.push(*in_tray);
                 } else {
                     skipped_one = true;
                 }
             });
 
+        assert!(skipped_one); // at least one should have been removed
+
         self.evaluate_spot_heading_right(
             &line_letters,
             line_cross_letters,
@@ -771,15 +771,27 @@ mod tests {
         });
 
         let mut ai = AI::new(difficulty, &dictionary);
-
+        let moves = ai.find_all_moves(&tray, &board);
         //let rng = SmallRng::seed_from_u64(123);
 
+        println!("Moves are {:?}", moves);
+
+        assert_eq!(moves.len(), 10);
+
+        tray.letters[4] = Some(
+            Letter {
+                text: ' ',
+                points: 0,
+                ephemeral: false,
+                is_blank: true,
+            }
+        );
+
         let moves = ai.find_all_moves(&tray, &board);
 
         println!("Moves are {:?}", moves);
 
         assert_eq!(moves.len(), 10);
-
     }
 
     #[test]