Disable negated matcher for rspec

Author: coorasse

CHANGELOG.md

@@ -1,5 +1,7 @@
 ## Unreleased
 
+* Disable `expect(...).not_to be_able_to(:action_a, :action_b)` for multiple actions because it leads to ambiguity. ([@coorasse][])
+
 ## 3.4.0
 
 * [#691](https://github.com/CanCanCommunity/cancancan/pull/691): Add two new subquery strategies: `joined_alias_exists_subquery`, `joined_alias_each_rule_as_exists_subquery`. ([@kaspernj][])

lib/cancan/matchers.rb

@@ -23,6 +23,15 @@
     end
   end
 
+  match_when_negated do |ability|
+    actions = args.first
+    if actions.is_a? Array
+      raise NotImplementedError, "`expect(...).not_to be_able_to(:action_a, :action_b)` is no longer supported.\nThis syntax leads to ambiguity and it has therefore been disabled.\nPlease split into separate expectations."
+    else
+      !ability.can?(*args)
+    end
+  end
+
   # Check that RSpec is < 2.99
   if !respond_to?(:failure_message) && respond_to?(:failure_message_for_should)
     alias_method :failure_message, :failure_message_for_should

spec/cancan/matchers_spec.rb

@@ -46,13 +46,11 @@
     end
 
     it 'delegates to can? with array of abilities with empty array' do
-      is_expected.not_to be_able_to([], 123)
+      expect { is_expected.not_to be_able_to([], 123) }.to raise_error(NotImplementedError)
     end
 
     it 'delegates to can? with array of abilities with only one eligible ability' do
-      is_expected.to receive(:can?).with(:read, 123) { true }
-      is_expected.to receive(:can?).with(:update, 123) { false }
-      is_expected.not_to be_able_to(%i[read update], 123)
+      expect { is_expected.not_to be_able_to(%i[read update], 123) }.to raise_error(NotImplementedError)
     end
   end
 end