Stride should allow zero size.

[danielgindi]

What's in this pull request?

People expect strides to allow zero size - like any traditional for loop that would have just skipped.
Adding an additional condition just for that makes the code messier.

But moreover - Xcode itself expects it to allow 0 length stride.
As Xcode automatically converts old for loops to strides, it actually breaks code that may in some cases have zero-length strides.

Example case:
ChartsOrg/Charts#931

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[tkremenek]

@swift-ci test

[tkremenek]

@dabrahams Please review.

[tkremenek]

@swift-ci test

[gribozavr]

Not a review of the semantics, but if we accept this change, it needs tests.

[tkremenek]

@danielgindi Please provide tests for this behavior change.

[danielgindi]

Ok friends, testing is always a good call.

After running some tests, I'm closing this.

I thought that this specific precondition tests for cases where the to is same as from, but it actually checks for interval - which should actually not be zero as it will almost always cause an infinite loop.

[dabrahams]

@danielgindi This may not be the right patch in the end, but your point Xcode migrating for loops has convinced me we a stride function that works for this case.

[danielgindi]

Yes- some work needs to be done on strides, but we need to carefully look into each case, and there are many of them.

• The interval may have weird sizes, or zero. (Zero is bad in for-loop also)
• The to/through may be less then from. There are many cases like these, where the loops should just be skipped. We had a few of them, but I've changed them before I realized that there's something wrong with the fact that the translation is not 1:1.
• Other cases are definitely out there