[Fix rubocop#5670] Suggest valid memoized instance variable for bang …

…method

See rubocop#5670 and rubocop#5648

CHANGELOG.md

@@ -9,6 +9,7 @@
 
 * [#5642](https://github.com/bbatsov/rubocop/pull/5642): Fix Style/Documentation :nodoc: for compact-style nested modules/classes. ([@ojab][])
 * [#5648](https://github.com/bbatsov/rubocop/issues/5648): Suggest valid memoized instance variable for predicate method. ([@satyap][])
+* [#5670](https://github.com/bbatsov/rubocop/issues/5670): Suggest valid memoized instance variable for bang method. ([@pocke][])
 * [#5623](https://github.com/bbatsov/rubocop/pull/5623): Fix `Bundler/OrderedGems` when a group includes duplicate gems. ([@colorbox][])
 * [#5633](https://github.com/bbatsov/rubocop/pull/5633): Fix broken `--fail-fast`. ([@mmyoji][])
 * [#5630](https://github.com/bbatsov/rubocop/issues/5630): Fix false positive for `Style/FormatStringToken` when using placeholder arguments in `format` method. ([@koic][])

lib/rubocop/cop/naming/memoized_instance_variable_name.rb

@@ -55,7 +55,7 @@ def on_def(node)
           msg = format(
             MSG,
             var: ivar_assign.children.first.to_s,
-            suggested_var: method_name.to_s.chomp('?'),
+            suggested_var: method_name.to_s.delete('!?'),
             method: method_name
           )
           add_offense(node, location: ivar_assign.source_range, message: msg)
@@ -66,7 +66,7 @@ def on_def(node)
 
         def matches?(method_name, ivar_assign)
           return true if ivar_assign.nil? || method_name == :initialize
-          method_name = method_name.to_s.sub('?', '')
+          method_name = method_name.to_s.delete('!?')
           variable = ivar_assign.children.first
           variable_name = variable.to_s.sub('@', '')
           variable_name == method_name

spec/rubocop/cop/naming/memoized_instance_variable_name_spec.rb

@@ -59,10 +59,8 @@ def foo
         end
       RUBY
     end
-  end
 
-  context 'memoized variable after other code does not match method name' do
-    it 'registers an offense' do
+    it 'registers an offense for a predicate method' do
       expect_offense(<<-RUBY.strip_indent)
         def foo?
           helper_variable = something_we_need_to_calculate_foo
@@ -71,6 +69,16 @@ def foo?
         end
       RUBY
     end
+
+    it 'registers an offense for a bang method' do
+      expect_offense(<<-RUBY.strip_indent)
+        def foo!
+          helper_variable = something_we_need_to_calculate_foo
+          @bar ||= calculate_expensive_thing(helper_variable)
+          ^^^^ Memoized variable `@bar` does not match method name `foo!`. Use `@foo` instead.
+        end
+      RUBY
+    end
   end
 
   context 'memoized variable matches method name' do
@@ -124,6 +132,16 @@ def a?
       end
     end
 
+    context 'memoized variable matches bang method name' do
+      it 'does not register an offense' do
+        expect_no_offenses(<<-RUBY.strip_indent)
+          def a!
+            @a ||= :foo
+          end
+        RUBY
+      end
+    end
+
     context 'code follows memoized variable assignment' do
       it 'does not register an offense' do
         expect_no_offenses(<<-RUBY.strip_indent)