Fix Range.disjoint?/2 for single-element ranges with a negative step#15582
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josevalim merged 1 commit intoJul 10, 2026
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`member?/2`, `size/1` and `to_list/1` all treat a single-element range
such as `1..1//-2` as the set `[1]`, and `Range.split/2` produces such
ranges from library code (e.g. `Range.split(5..1//-2, 2)` yields
`1..1//-2`). Yet `disjoint?/2` reported two of them as sharing no
element:
Range.disjoint?(1..1//-2, 1..1//-2) #=> true (should be false)
`normalize/3` only reversed ranges when `first > last`, leaving a
negative step in place for single-element ranges (`first == last`). The
arithmetic-progression intersection in `disjoint?/2` assumes an
increasing progression, so the leftover negative step produced a wrong
result. The `step == -1` case was masked by the `abs(step) == 1`
shortcut, so only `step <= -2` was affected.
Assisted-by: Claude Code:claude-opus-4-8
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member?/2,size/1andto_list/1all treat a single-element range such as1..1//-2as the set[1], andRange.split/2produces such ranges from library code (e.g.Range.split(5..1//-2, 2)yields1..1//-2). Yetdisjoint?/2reported two of them as sharing no element:normalize/3only reversed ranges whenfirst > last, leaving a negative step in place for single-element ranges (first == last). The arithmetic-progression intersection indisjoint?/2assumes an increasing progression, so the leftover negative step produced a wrong result. Thestep == -1case was masked by theabs(step) == 1shortcut, so onlystep <= -2was affected.Assisted-by: Claude Code:claude-opus-4-8