Fix Iterators.sequence dropping the last element of a stepped range

[thswlsqls]

Fixes #

hudson.util.Iterators.sequence(start, end, step) (public, @since 1.150) sizes the list as (end - start) / step, truncating toward zero. When the half-open [start, end) length isn't a multiple of step, the last element is silently dropped — e.g. sequence(1, 6, 2) returns [1, 3] instead of [1, 3, 5]; sequence(0, 10, 3) and sequence(10, 0, -3) likewise drop their last element.

The fix uses ceiling division correct for both step signs, keeping the negative-size guard for inverted ranges. Both in-tree callers (Fingerprint.java:366/:379) use step ±1 under start < end, so in-tree output is unchanged — no regression; only external non-±1-step callers regain the dropped element.

Testing done

Added IteratorsTest.sequenceWithNonUnitStep: the three buggy cases return the full range, plus exact-multiple and empty-range guards. mvn -pl core -am clean test -Dtest=IteratorsTest (JDK 21): 6 tests, 0 failures.

Screenshots (UI changes only)

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After

Proposed changelog entries

• Fix Iterators.sequence dropping the last element of a stepped range whose length is not a multiple of the step

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/label bug

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N/A

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[daniel-beck]

Closing per #26359.