[GROOVY-8537] GroovyCollections.combinations(Iterable) exhibits incorrect (asymmetric) behavior

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.4.15
• Fix Version/s: 3.0.0-alpha-2, 2.6.0-alpha-4, 2.4.16, 2.5.0-rc-2
• Component/s: groovy-jdk
• Labels: easyfix
• Assignee: Paul King
• Reporter: Venkatesh-Prasad Ranganath
• Created: 08/Apr/18 02:28
• Updated: 26/Jul/18 04:38
• Resolved: 11/Apr/18 06:42

Description

Issue

When GroovyCollections.combinations() is invoked on a collection of iterables with at least one empty iterable, the expected return value is an empty list of combinations.

Instead, in version 2.4.15 (and I am guessing in earlier versions at least since 2.2.0), the return value of combinations() is sensitive to the order of iterables in the input collection.  Here are two instances of such behavior.

Repro

groovy:000> assert [[1,3], []].combinations() == [[], [1,3]].combinations()
ERROR org.codehaus.groovy.runtime.powerassert.PowerAssertionError:
assert [[1,3], []].combinations() == [[], [1,3]].combinations()
                   |              |              |
                   []             false          [[1], [3]]

 

groovy:000> assert [[1,3], [2], []].combinations() == [[1,3], [], [2]].combinations()
ERROR org.codehaus.groovy.runtime.powerassert.PowerAssertionError:
assert [[1,3], [2], []].combinations() == [[1,3], [], [2]].combinations()
                        |              |                   |
                        []             false               [[2]]

Fix

Add a short-circuiting check at the start of combinations(Iterable) method to return an empty list of combination if any of the input iterables are empty.

Issue Links

• links to: GitHub Pull Request #682