Do recursive shrinking without recursive function calls #1

neithernut · 2022-12-04T21:19:31Z

We try to shrink values recursively, i.e. when a shrunk value witnesses a failure, we'd shrink that value further. Previously, this recursion would be implemented via actual control flow recursion, i.e. a function calling itself. Since the recursion could not be unrolled by the compiler, this could result in stack overflows in some situations. Albeit such an overflow would often hint at a faulty shrinker (e.g. a shrinker yielding the original value), the stack overflow could also occur in other situations. This change switches from a recursive control flow to explicitly swapping out the shrinking iterator during the iteration.

In the past, shrinking was implemented using recursion in the control flow. `shrink_failure` would call itself. That function was introduced originally in 5b19e7c presumably in order to implement recursive shrinking. However, we recently choose an approach which would not rely on recursive control flow but on swapping out an iterator. Thus, the reason why `shrink_failure` existed in the first place doesn't exist any more. This change moves the logic in its original place, but also replaces the `match` which enclosed the call to `shrink_failure` with an `if`.

neithernut added 2 commits June 12, 2021 13:12

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Do recursive shrinking without recursive function calls #1

Do recursive shrinking without recursive function calls #1

neithernut commented Dec 4, 2022

Do recursive shrinking without recursive function calls #1

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Do recursive shrinking without recursive function calls #1

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neithernut commented Dec 4, 2022