A new version of System was added to project The Inbox:
http://source.squeak.org/inbox/System-ct.1246.mcz

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

Name: System-ct.1246
Author: ct
Time: 1 November 2021, 10:02:52.192754 pm
UUID: 1a72b404-61d8-d04c-8323-6a94bceb2230
Ancestors: System-eem.1244

Avoids dangling preferences when removing the preference pragma from a method.

The disadvantage of this approach is that the lifecycle of the preference is reset whenever it is recompiled. However, I am not aware of any disadvantage of this change.

=============== Diff against System-eem.1244 ===============

Item was changed:
  ----- Method: Preferences class>>prefEvent: (in category 'updating') -----
  prefEvent: anEvent
  	"Check if this system event defines or removes a preference."
  
  	| class selector method |
  	self flag: #performance. "mt: Maybe defer preference dictionary update?"
  
  	anEvent itemKind = SystemChangeNotifier classKind ifTrue: [
  		anEvent isRemoved ifTrue: [
  			self removeAllPreferencesSuchThat: [:pref | 
  				pref provider == anEvent item]].
  		
  		anEvent isRenamed ifTrue: [
  			self atomicUpdatePreferences: [ :prefs |
  				self allPreferences
  					select: [:pref | pref provider == anEvent item]
  					thenDo: [:pref | prefs at: pref id put: pref].
  				prefs keys
  					select: [:id | id beginsWith: anEvent oldName]
  					thenDo: [:id | prefs removeKey: id] ] ] ].
  	
  	anEvent itemKind = SystemChangeNotifier methodKind ifTrue: [
  		"ignore instance methods"
  		anEvent itemClass isMeta
  			ifFalse: [^ self]. 
+ 		
- 
  		class := anEvent itemClass theNonMetaClass.
  		selector := anEvent itemSelector.
  		method := anEvent item.
+ 		
+ 		self atomicUpdatePreferences: [ :prefs | 
+ 			"See PragmaPreference >> #id."
+ 			prefs removeKey: (class name,'>>', selector) asSymbol ifAbsent: []] .
+ 		
- 
- 		anEvent isRemoved ifTrue: [
- 			self atomicUpdatePreferences: [ :prefs | 
- 				"See PragmaPreference >> #id."
- 				prefs removeKey: (class name,'>>', selector) asSymbol ifAbsent: []]].
- 	
  		(anEvent isAdded or: [anEvent isModified]) ifTrue: [
  			method pragmas do: [:pragma | self addPragmaPreference: pragma] ] ].!