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Negating an integer leads to stack overflow #301

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Heroglyph opened this issue Oct 1, 2021 · 3 comments
Open

Negating an integer leads to stack overflow #301

Heroglyph opened this issue Oct 1, 2021 · 3 comments

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@Heroglyph
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MWE:

use quickcheck::quickcheck;

#[test]
fn negate_value() {
    fn prop(i: i8) -> bool {
        -i;
        true
    }
    
    quickcheck(prop as fn(i8) -> bool);
}

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?

@neithernut
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The endless recursion is likely a symptom of i8's shrinker yielding the original value. See #295 for a related issue.Could you check whether #296 resolves your issue?

@Heroglyph
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Author

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!

dead-claudia added a commit to dead-claudia/journald-exporter that referenced this issue Jul 6, 2024
...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.
@Velnbur
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Velnbur commented Oct 7, 2024

Encountered this issue with i32 too on current main

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