Pass

Very well done Oliver!

Only 284 lines! Whoah.

You made the most of the template; I'm happy.

The little code you wrote yourself looks good.

Thanks! :D

Some tips:

• Use conditional match statements to avoid copy-paste.
  Your code:

match self.selected_square {
    Some(pos) => {
        if pos == (rank, file) {
            self.selected_square = None;
            self.highlighted_squares = Vec::new();
        } else if self.highlighted_squares.iter().any(|p| p == &(rank,file)) {
            self.game.take_turn(move_string(pos, (rank,file)));
            self.selected_square = None;
            self.highlighted_squares = Vec::new();
        } else {
            self.selected_square = Some((rank, file));
            self.highlighted_squares = Vec::new();
            if let Some(c) = get_colour(self.game.board[rank][file]) {
                if c == self.game.current_turn {
                    self.highlighted_squares = self.game.board[rank][file].get_valid_moves( (rank, file), &self.game.board, self.game.en_passant_square, self.game.castlings, self.game.current_turn);
                };
            };
        }
    },
    None => {
        self.selected_square = Some((rank, file));
        self.highlighted_squares = Vec::new();
        if let Some(c) = get_colour(self.game.board[rank][file]) {
            if c == self.game.current_turn {
                self.highlighted_squares = self.game.board[rank][file].get_valid_moves( (rank, file), &self.game.board, self.game.en_passant_square, self.game.castlings, self.game.current_turn);
            };
        };
    }
}

With conditional match cases:

match self.selected_square {
    Some(pos) if pos == (rank, file) => {
        self.selected_square = None;
        self.highlighted_squares = Vec::new();
    },
    Some(pos) if self.highlighted_squares.iter().any(|p| p == &(rank,file)) => {
        self.game.take_turn(move_string(pos, (rank,file)));
        self.selected_square = None;
        self.highlighted_squares = Vec::new();
    },
    _ => {
        self.selected_square = Some((rank, file));
        self.highlighted_squares = Vec::new();
        if let Some(c) = get_colour(self.game.board[rank][file]) {
            if c == self.game.current_turn {
                self.highlighted_squares = self.game.board[rank][file].get_valid_moves( (rank, file), &self.game.board, self.game.en_passant_square, self.game.castlings, self.game.current_turn);
            };
        };
    }
}

• Use arithmetics to avoid branching.
  Your code:

string.push(match _from.1 {
    0 => 'a',
    1 => 'b',
    2 => 'c',
    3 => 'd',
    4 => 'e',
    5 => 'f',
    6 => 'g',
    7 => 'h',
    _ => panic!("File wrong")
});
match _from.0 {
    0..=7 => string.push(char::from_digit(8 - _from.0 as u32, 10).unwrap()),
    _ => panic!("Rank wrong"),
};
string.push(' ');
string.push(match _to.1 {
    0 => 'a',
    1 => 'b',
    2 => 'c',
    3 => 'd',
    4 => 'e',
    5 => 'f',
    6 => 'g',
    7 => 'h',
    _ => panic!("File wrong")
});
match _to.0 {
    0..=7 => string.push(char::from_digit(8 - _to.0 as u32, 10).unwrap()),
    _ => panic!("Rank wrong"),
};

With arithmetics:

// I would write this as a helper-function instread of a closure.
let parse_push_coord = |_coord: (usize, usize), _s: &mut String| {
    _s.push(match _coord.1 {
        0..=7 => (_coord + 97) as u8 as char,
        _ => panic!("File wrong")
    }) 
    match _coord.0 {
        0..=7 => string.push(char::from_digit(8 - _coord.0 as u32, 10).unwrap()),
        _ => panic!("Rank wrong"),
    };
};

parse_push_coord(_from, &mut _s);
string.push(' ');
parse_push_coord(_to, &mut _s);

No source file or test is named. Start by locating the self.selected_square match and coordinate-string construction shown in the issue, then verify that the suggested refactoring preserves chess move selection and coordinate formatting behavior.