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Negating an integer leads to stack overflow #301
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I checked by trying the current BurntShushi:master and neithernut:i32min-shrink-bound (revision 0c279d6). The latter revision (yours), fixed the issue, so merging the pull request should resolve my problem. Thank you! |
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...and switch the 32-bit integer parser to just exhaustive checking. (More on that later.) Why move away from QuickCheck? 1. The maintainer appears to have little interest in actually maintaining it. BurntSushi/quickcheck#315 2. Its API is incredibly inefficient, especially on failure, and it's far too rigid for my needs. For one, I need something looser than `Arbitrary: Clone` so things like `std::io::Error` can be generated more easily. Also, with larger structures, efficiency will directly correlate to faster test runs. Also, I've run into the limitations of not being able to access the underlying random number generator far too many times to count, as I frequently need to generate random values within ranges, among other things. - BurntSushi/quickcheck#279 - BurntSushi/quickcheck#312 - BurntSushi/quickcheck#320 - BurntSushi/quickcheck#267 3. It correctly limits generated `Vec` and `String` length, but it doesn't similarly enforce limits on test length. 4. There's numerous open issues in it that I've addressed, in some cases by better core design. To name a few particularly bad ones: - Misuse of runtime bounds in `Duration` generation, `SystemTime` generation able to panic for unrelated reasons: BurntSushi/quickcheck#321 - Incorrect generation of `SystemTime`: BurntSushi/quickcheck#321 - Unbounded float shrinkers: BurntSushi/quickcheck#295 - Avoiding pointless debug string building: BurntSushi/quickcheck#303 - Signed shrinker shrinks to the most negative value, leading to occasional internal panics: BurntSushi/quickcheck#301 There's still some room for improvement, like switching away from a recursive loop: BurntSushi/quickcheck#285. But, this is good enough for my use cases right now. And this code base is structured such that such a change is *much* easier to do. (It's also considerably simpler.) As for the integer parser change, I found a way to re-structure it so I could perform true exhaustive testing on it. Every code path has every combination of inputs tested, except for memory space as a whole. This gives me enough confidence that I can ditch the randomized property checking for it.
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MWE:
I think that quickcheck tests this function with the smallest integer, which panics because it cannot be negated due to two's complement. So far, so correct. The resulting panic is then caught and correctly interpreted to be caused by a failed test. However, attempting to shrink the value causes another panic, which causes another attempt at shrinking, causing another panic and so on, ultimately resulting in a stack overflow as the shrinking functions pile on top of each other. This seems to be a bug in the way that shrinking is done (because it keeps testing the same value).
How do we proceed?
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