From ae682c0bb583d8912f07fd922dde544cf424dd0c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?fn=20=E2=8C=83=20=E2=8C=A5?=
 <70830482+FnControlOption@users.noreply.github.com>
Date: Fri, 2 Sep 2022 17:23:14 -0700
Subject: [PATCH] Add autocorrect for `Style/StaticClass`

---
 ..._add_autocorrect_for_style_static_class.md |  1 +
 lib/rubocop/cop/style/static_class.rb         | 33 +++++++++++++++-
 spec/rubocop/cop/style/static_class_spec.rb   | 39 +++++++++++++++++++
 3 files changed, 72 insertions(+), 1 deletion(-)
 create mode 100644 changelog/new_add_autocorrect_for_style_static_class.md

diff --git a/changelog/new_add_autocorrect_for_style_static_class.md b/changelog/new_add_autocorrect_for_style_static_class.md
new file mode 100644
index 00000000000..ea6e2ae69bf
--- /dev/null
+++ b/changelog/new_add_autocorrect_for_style_static_class.md
@@ -0,0 +1 @@
+* Add autocorrect for `Style/StaticClass`. ([@FnControlOption][])
diff --git a/lib/rubocop/cop/style/static_class.rb b/lib/rubocop/cop/style/static_class.rb
index 446b90f5f3a..2cdaa99824c 100644
--- a/lib/rubocop/cop/style/static_class.rb
+++ b/lib/rubocop/cop/style/static_class.rb
@@ -44,18 +44,49 @@ module Style
       #   end
       #
       class StaticClass < Base
+        include RangeHelp
         include VisibilityHelp
+        extend AutoCorrector
 
         MSG = 'Prefer modules to classes with only class methods.'
 
         def on_class(class_node)
           return if class_node.parent_class
+          return unless class_convertible_to_module?(class_node)
 
-          add_offense(class_node) if class_convertible_to_module?(class_node)
+          add_offense(class_node) do |corrector|
+            autocorrect(corrector, class_node)
+          end
         end
 
         private
 
+        def autocorrect(corrector, class_node)
+          corrector.replace(class_node.loc.keyword, 'module')
+          corrector.insert_after(class_node.loc.name, "\nmodule_function\n")
+
+          class_elements(class_node).each do |node|
+            if node.defs_type?
+              autocorrect_def(corrector, node)
+            elsif node.sclass_type?
+              autocorrect_sclass(corrector, node)
+            end
+          end
+        end
+
+        def autocorrect_def(corrector, node)
+          corrector.remove(
+            range_between(node.receiver.source_range.begin_pos, node.loc.name.begin_pos)
+          )
+        end
+
+        def autocorrect_sclass(corrector, node)
+          corrector.remove(
+            range_between(node.loc.keyword.begin_pos, node.identifier.source_range.end_pos)
+          )
+          corrector.remove(node.loc.end)
+        end
+
         def class_convertible_to_module?(class_node)
           nodes = class_elements(class_node)
           return false if nodes.empty?
diff --git a/spec/rubocop/cop/style/static_class_spec.rb b/spec/rubocop/cop/style/static_class_spec.rb
index 26cab4e0a16..0ffb33ec0d4 100644
--- a/spec/rubocop/cop/style/static_class_spec.rb
+++ b/spec/rubocop/cop/style/static_class_spec.rb
@@ -8,6 +8,14 @@ class C
         def self.class_method; end
       end
     RUBY
+
+    expect_correction(<<~RUBY)
+      module C
+      module_function
+
+        def class_method; end
+      end
+    RUBY
   end
 
   it 'registers an offense when class has `class << self` with class methods' do
@@ -21,6 +29,18 @@ def other_class_method; end
         end
       end
     RUBY
+
+    expect_correction(<<~RUBY)
+      module C
+      module_function
+
+        def class_method; end
+
+       #{trailing_whitespace}
+          def other_class_method; end
+       #{trailing_whitespace}
+      end
+    RUBY
   end
 
   it 'does not register an offense when class has `class << self` with macro calls' do
@@ -44,6 +64,16 @@ class C
         def self.class_method; end
       end
     RUBY
+
+    expect_correction(<<~RUBY)
+      module C
+      module_function
+
+        CONST = 1
+
+        def class_method; end
+      end
+    RUBY
   end
 
   it 'does not register an offense when class has instance method' do
@@ -103,6 +133,15 @@ class C
         def self.class_method; end
       end
     RUBY
+
+    expect_correction(<<~RUBY)
+      module C
+      module_function
+
+        extend M
+        def class_method; end
+      end
+    RUBY
   end
 
   it 'does not register an offense for modules' do