Fix potential infinite loop or recursion when computing size of infinite cyclic groups #3580
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fingolfin
added
kind: bug
This method needs to test whether a group element is the identity; but this can lead to an infinite recursion if the input is an fp group, as then this equality check may end up trying to compute the group size. This currently actually happens when all packages are loaded (with only the default set of filters, another Size method is selected for cyclic fp groups). We fix this by adding the `CanEasilyCompareElements` filter to the argument filters of the method. Strictly speaking, we'd also want to check for something like `CanEasilyComputerElementOrder`, but that doesn't exist.
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Codecov Report
@@ Coverage Diff @@
## master #3580 +/- ##
==========================================
- Coverage 84.46% 84.1% -0.36%
==========================================
Files 696 647 -49
Lines 345127 319567 -25560
==========================================
- Hits 291497 268779 -22718
+ Misses 53630 50788 -2842
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DominikBernhardt
approved these changes
Jul 17, 2019
DominikBernhardt
added
release notes: added
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This method needs to test whether a group element is the identity; but this
can lead to an infinite recursion if the input is an fp group, as then this
equality check may end up trying to compute the group size. This currently
actually happens when all packages are loaded (with only the default set of
filters, another Size method is selected for cyclic fp groups).
We fix this by adding the
CanEasilyCompareElementsfilter to the argumentfilters of the method. Strictly speaking, we'd also want to check for
something like
CanEasilyComputerElementOrder, but that doesn't exist.