RmFinalEpsilon: Only remove epsilon arcs if semiring is left distributive or state is non-final#75
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…tive or state is non-final Pushing final weights backward across an epsilon transition (folding `arc.weight * final_weight` into the current state's final weight) inherently assumes left distributivity: `A * (B + C) = A * B + A * C`. For semirings that are not left distributive (such as `StringWeight` with `STRING_RIGHT`), unconditionally folding these weights alters the accepted semantics of the FST. This change ensures that `RmFinalEpsilon` only sums up epsilon arcs if the semiring has the `kLeftSemiring` property, fixing test failures in `algo_test_right_string` (`MyMap/MapTest/0.EncodeDestructive`). PiperOrigin-RevId: 901317228
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RmFinalEpsilon: Only remove epsilon arcs if semiring is left distributive or state is non-final
Pushing final weights backward across an epsilon transition (folding
arc.weight * final_weightinto the current state's final weight)inherently assumes left distributivity:
A * (B + C) = A * B + A * C.For semirings that are not left distributive (such as
StringWeightwith
STRING_RIGHT), unconditionally folding these weights alters theaccepted semantics of the FST.
This change ensures that
RmFinalEpsilononly sums up epsilon arcs ifthe semiring has the
kLeftSemiringproperty, fixing test failures inalgo_test_right_string(MyMap/MapTest/0.EncodeDestructive).