Fix IndexError in read_game on an unmatched ) after an illegal move - #1204
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eeshsaxena wants to merge 1 commit into
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Fix IndexError in read_game on an unmatched ) after an illegal move#1204eeshsaxena wants to merge 1 commit into
eeshsaxena wants to merge 1 commit into
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read_game recovers from an illegal move by entering skip mode, and a later unmatched ')' closes that skip by calling end_variation(). When the error happened on the mainline there was no matching begin_variation(), so the unconditional variation_stack.pop() removed the root game node, leaving the stack empty and making the next visit_move() raise IndexError. Keep the root on the stack, mirroring the assert in begin_variation().
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Came across this feeding some scraped PGNs through read_game: a short game like
raises
IndexError: list index out of rangefromGameBuilder.visit_moveinstead of being parsed with the bad move recorded ingame.errors.What happens:
Nf3is illegal for Black, so the parser callshandle_errorand setsskip_variation_depth = 1to skip to the end of the (assumed) variation. The following)closes that skip and callsend_variation(), but since the error was on the mainline there was never a matchingbegin_variation().end_variation()popsvariation_stackunconditionally, so it removes the root game node and empties the stack; the next move (e5) then doesself.variation_stack[-1]and raises IndexError.read_gamealready guards the normal)path withlen(board_stack) > 1, andbegin_variation()asserts the root is never pushed as a variation, so I madeend_variation()symmetric: it keeps the root on the stack. With that, the example parses to thee4 e5mainline with one recorded error, and real variations are unaffected.Extended test_variation_stack with this case (it sits right next to the existing superfluous-bracket cases). It raises IndexError on master and passes with the change; the full PGN test suite still passes. Found it by fuzzing read_game with mutated PGNs.