Fix ReducibleLaws causing stack overflow by calling Eval.now early
#3565
Conversation
The test `reduceRightConsistentWithReduceRightOption` currently calls `value` on an `Eval` before the end of the computation, i.e. inside the functions passed to `reduceRight` and `reduceRightOption`. This can cause a stack overflow in otherwise lawful `Reducible` instances. The test has been changed to instead use `map` on the `Eval` which is the intended way of using `Eval` in methods like `reduceRight`.
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It would be hard for me to write a test for this behaviour, it only happens in a complex and recursive data-type* which I have defined a I did check if this test was intentionally written like this on Gitter before opening this PR but got no response, I'm pretty sure it is a mistake in the way the laws test is written though. (https://gitter.im/typelevel/cats?at=5f3165af733c00338f036dbd). I also checked the other laws suites for cases of * The type I see the failure for is a zipper for navigating a rose tree (multi-way tree), the // Scala 2.13 LazyList
final case class Tree[A](rootLabel: A, subForest: LazyList[Tree[A]])
type TreeForest[A] = LazyList[Tree[A]]
type Parent[A] = (TreeForest[A], A, TreeForest[A])
type Parents[A] = LazyList[Parent[A]]
final case class TreeLoc[A](tree: Tree[A], lefts: TreeForest[A], rights: TreeForest[A], parents: Parents[A]) |
Codecov Report
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## master #3565 +/- ##
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Coverage 91.26% 91.26%
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Files 386 386
Lines 8587 8587
Branches 235 237 +2
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Hits 7837 7837
Misses 750 750 |
The test
reduceRightConsistentWithReduceRightOptioncurrently callsvalueon anEvalbefore the end of the computation, i.e. it callsvalueinside the functions passed to
reduceRightandreduceRightOption.This can cause a stack overflow in otherwise lawful
Reducibleinstances.The test has been changed to instead use
mapon theEvalwhich isthe intended way of using
Evalin methods likereduceRight.