Restart engine when bot exceeds per-move time limit

[MarkZH]

Type of pull request:

• Bug fix
• Feature
• Other

Description:

If a user specifies a per-move time limit in their configuration file--e.g., uci_options: go_commands: movetime: 1000 for 1000 milliseconds per move--and the engine exceeds this time limit by more than 10 seconds, the python-chess library will intervene and cancel the search while raising a TimeoutError. Previously, this error would be caught and main play_game() loop would carry on without sending a move to lichess.org.

Now, the TimeoutError is propagated until it hits the backoff decoration of play_game(). This shuts down the engine (correctly, now, due to changes in engine_wrapper.py) and restarts it when backoff restarts play_game(). Even if the engine keeps exhibiting the same buggy behavior, the errors will be displayed on the terminal and log, so the user will know that something is wrong.

Related Issues:

This PR closes #893 and should be a better solution to #623 than the previous PR #628.

Checklist:

• I have read and followed the contribution guidelines.
• I have added necessary documentation (if applicable).
• The changes pass all existing tests.

[MarkZH]

To see the changes to test_bot/test_bot.py, hide the whitespace changes. Since the buggy_engine made for the new test can only play a set list of moves, I had to change the thread_for_test() to allow changing the opponent to something other than stockfish.

[AttackingOrDefending]

The docstring should be changed since we don't use stockfish.

[AttackingOrDefending]

lichess-bot plays black so it always receieves an odd number of moves, so the engine that waits for 11 seconds is the outside engine and not the one managed by lichess-bot. You can change buggy_engine.py to

"""An engine that takes too much time to make a move during tests."""

import chess
import time

assert input() == "uci"

print("id name Delay tactic", flush=True)
print("id author MZH", flush=True)
print("uciok", flush=True)

delay_performed = False
just_started = True
scholars_mate = ["a2a3", "e7e5", "a3a4", "f8c5", "a4a5", "d8h4", "a5a6", "h4f2"]

while True:
    command, *remaining = input().split()
    if command == "quit":
        break
    elif command == "isready":
        print("readyok", flush=True)
    elif command == "position":
        spec_type, *remaining = remaining
        assert spec_type == "startpos"
        board = chess.Board()
        if remaining:
            moves_label, *move_list = remaining
            assert moves_label == "moves"
            for move in move_list:
                board.push_uci(move)
        if just_started and len(board.move_stack) > 1:
            delay_performed = True
    elif command == "go":
        move_count = len(board.move_stack)
        if move_count == 3 and not delay_performed:
            print("info string delaying move", flush=True)
            delay_performed = True
            time.sleep(12)
        move = scholars_mate[move_count]
        print(f"bestmove {move}", flush=True)
        just_started = False

and line 346 in test_bot.py to CONFIG["engine"]["uci_options"] = {"go_commands": {"movetime": 100}}.

[MarkZH]

I'm going to fix this PR so the git blame for test_bot.py isn't rendered completely useless. I think my editor changed the newlines on every line.

[MarkZH]

This PR is replaced by #897 to reduce clutter due to whitespace issues.