fix move parsing bug

src/board.rs

@@ -168,9 +168,9 @@ impl Board {
         Self::from_fen(fen_parts.collect::<Vec<&str>>().as_slice())
     }
 
-    pub fn parse_move(&self, mov: &str) -> Result<Move, ()> {
+    pub fn parse_move(&self, mov: &str) -> Result<Move, String> {
         if mov.len() < 4 {
-            Err(())
+            Err("string too short".to_owned())
         }
         else {
             let origin = Move::parse_square(&mov[0..2]);
@@ -182,7 +182,7 @@ impl Board {
                     Some('N') | Some('n') => KNIGHT,
                     Some('B') | Some('b') => BISHOP,
                     Some('R') | Some('r') => ROOK,
-                    _ => panic!("invalid move: {}", mov)
+                    _ => return Err("invalid promotion".to_owned())
                 })
             }
             else {
@@ -190,7 +190,7 @@ impl Board {
             };
 
             if let (Some(from), Some(to)) = (origin, target) {
-                let (piece_type, side) = self.get_square(from).unwrap_or(Err(())?);
+                let (piece_type, side) = self.get_square(from).ok_or("no piece at from square")?;
                 //println!("from: {}", from);
 
                 let target = self.get_square(to);
@@ -198,19 +198,19 @@ impl Board {
 
                 if let Some((_cap, cs)) = target {
                     if cs == side {
-                        // cannot capture own piece
-                        return Err(());
+                        return Err("cannot capture own piece".to_owned());
                     }
                 }
 
 
-                if side != self.turn { // wrong side to move
-                    return Err(());
+                if side != self.turn {
+                    return Err("wrong side to move".to_owned());
                 }
 
                 if let Some(promote_to) = promote_to {
                     if piece_type != PAWN {
-                        return Err(());
+                        // should never happen
+                        return Err("cannot promote to pawn".to_owned());
                     }
                     Ok(Move::Promotion{ mov: SimpleMove{ from, to }, pc: PieceCaptureType::new(promote_to, captured) })
                 }
@@ -237,7 +237,7 @@ impl Board {
                 }
             }
             else {
-                Err(())
+                Err("no valid squares".to_owned())
             }
         }
     }

src/engine.rs

@@ -157,7 +157,7 @@ impl Engine {
             }
             else {
                 println!("{}", self.board.beautiful_print());
-                println!("error parsing move {}", mov);
+                println!("error parsing move {}: {}", mov, m.err().unwrap_or(String::new()));
                 break;
             }
         }