Explictly call Ord::cmp to compare priorities #85
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Previously we would call `PartialOrd::partial_cmp` implicilty using the overloaded comparison operators `>` and `<` when comparing priorities, despite the fact that P is required to be `Ord`. A well behaved implementation of `partial_cmp` is supposed to return `Some(Ord::cmp(self, other))`. That relationship is only a convention, so a misbehaved implementation may return None, which may cause the order items are popped from the queue to behave seemingly randomly. We can be a bit more defensive here and instead always call `Ord::cmp` directly, ensuring that we never try to compare things that could possibly return `None`. In order to enforce this going forward I added a test that panics in the implementation for partial_cmp and exercised all of the code paths that might call it. This isn't perfect, since new callsites could be added, but I figure its probably good enough for now. Not sure exactly how to version this, it's not a breaking change if you implementation of `PartialOrd` follows the convention, but if you don't it would be a breaking change, since we'd be using a different function for comparisons.
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Following up discussion in #84
Previously we would call
PartialOrd::partial_cmpimplicilty using the overloaded comparison operators>and<when comparing priorities, despite the fact that P is required to beOrd. A well behaved implementation ofpartial_cmpis supposed to returnSome(Ord::cmp(self, other)). That relationship is only a convention, so a misbehaved implementation may return None, which may cause the order items are popped from the queue to behave seemingly randomly.We can be a bit more defensive here and instead always call
Ord::cmpdirectly, ensuring that we never try to compare things that could possibly returnNone. In order to enforce this going forward I added a test that panics in the implementation for partial_cmp and exercised all of the code paths that might call it. This isn't perfect, since new callsites could be added, but I figure its probably good enough for now.Not sure exactly how to version this, it's not a breaking change if your implementation of
PartialOrdfollows the convention, but if you don't it would be a breaking change, since we'd be using a different function for comparisons.