Christoph Thiede uploaded a new version of Regex-Core to project The Trunk:
http://source.squeak.org/trunk/Regex-Core-ct.62.mcz

==================== Summary ====================

Name: Regex-Core-ct.62
Author: ct
Time: 23 August 2021, 5:27:14.776768 pm
UUID: 3a47183c-32cd-ee44-bf87-01eab0ec2ce5
Ancestors: Regex-Core-mt.61

Fixes copying of cyclic RxmLink structures. This fixes the #testNestedQuantifiers failure from Regex-Tests-Core-ct.17.

Nevertheless, I am not sure whether this is the right solution and whether cyclic RxmLinks are actually healthy, so it might be better if someone could review this ...

=============== Diff against Regex-Core-mt.61 ===============

Item was changed:
  ----- Method: RxmLink>>copyUsing: (in category 'copying') -----
  copyUsing: anIdentityDictionary
  	"Copy the receiver if it's not present in the argument dictionary, or just return the previously made copy. The rest of the object graph will be copied by #postCopyUsing:."
  
  	^anIdentityDictionary 
  		at: self
  		ifAbsent: [
  			"It may be tempting to use #at:ifAbsentPut: instead, but the argument block must not modify the receiver, so that wouldn't work."
+ 			(anIdentityDictionary
- 			anIdentityDictionary
  				at: self
+ 				put: self shallowCopy)
- 				put: (self shallowCopy
  					postCopyUsing: anIdentityDictionary;
+ 					yourself ]!
- 					yourself) ]!