negated matcher for be_able_to only passes when no ability is eligible

CHANGELOG.md

@@ -1,3 +1,7 @@
+## Unreleased
+
+* [#645](https://github.com/CanCanCommunity/cancancan/issues/645): Generate inner queries instead of join+distinct. ([@mraidel][], [@gabsi20][])
+
 ## 3.1.0
 
 * [#605](https://github.com/CanCanCommunity/cancancan/pull/605): Generate inner queries instead of join+distinct. ([@fsateler][])
@@ -665,3 +669,5 @@ Please read the [guide on migrating from CanCanCan 2.x to 3.0](https://github.co
 [@aleksejleonov]: https://github.com/aleksejleonov
 [@albb0920]: https://github.com/albb0920
 [@ayumu838]: https://github.com/ayumu838
+[@mraidel]: https://github.com/mraidel
+[@gabsi20]: https://github.com/gabsi20

lib/cancan/matchers.rb

@@ -11,14 +11,17 @@
 
 Kernel.const_get(rspec_module)::Matchers.define :be_able_to do |*args|
   match do |ability|
-    actions = args.first
-    if actions.is_a? Array
-      break false if actions.empty?
+    actions = Array(args.first)
+    break false if actions.empty?
 
-      actions.all? { |action| ability.can?(action, *args[1..-1]) }
-    else
-      ability.can?(*args)
-    end
+    actions.all? { |action| ability.can?(action, *args[1..-1]) }
+  end
+
+  match_when_negated do |ability|
+    actions = Array(args.first)
+    break true if actions.empty?
+
+    actions.none? { |action| ability.can?(action, *args[1..-1]) }
   end
 
   # Check that RSpec is < 2.99

spec/cancan/matchers_spec.rb

@@ -49,10 +49,12 @@
       is_expected.not_to be_able_to([], 123)
     end
 
-    it 'delegates to can? with array of abilities with only one eligable ability' do
+    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)
+      is_expected.not_to receive(:can?).with(:update, 123)
+      expect do
+        is_expected.not_to be_able_to(%i[read update], 123)
+      end.to raise_error('expected not to be able to [:read, :update] 123')
     end
   end
 end