[4.2] Make upperBound != 0 a precondition for RNG.next(upperBound:) (#17627) #17631
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…ang#17627) The function's definition is "Returns a random value that is less than the given upper bound," which cannot possibly be satisfied with upperBound == 0; previously the function returned zero, which was a bug.
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The function's definition is "Returns a random value that is less than the given upper bound," which cannot possibly be satisfied with upperBound == 0; previously the function returned zero, which was a bug.
Resolves SR-8143 and rdar://problem/41735302.
Explanation: Without this change,
RNG.next(upperBound: bound)can return a value that does not satisfy the invariantbound < upperBound.Scope: Minor, but we want to be able to guarantee this invariant holds.
Issue #: https://bugs.swift.org/browse/SR-8143
Risk: Very low.
Testing: Standard regression tests. Random is a new feature, and this only fixes an error case.
Reviewer: @lorentey