We've long hidden the index from the user. Did we change that in the previous PR?

Let’s please add some tests. I would think you could copy the example from the bug report and check if global.i is defined, or maybe make the test function "use strict"?

@vendethiel the previous PR (#4855) changed variable declaration of the index, e.g. i:

# before
i = o.scope.freeVariable 'i', single: true

#after
i = o.scope.freeVariable 'i', single: true, reserve: no

The former declared i in the global scope.

The other thing, which I didn't notice before, but #4882 has found, is the different output of the for statement between range with number literals ([0..50]) and variables ([0..a]) in Range::compileArray.