Enhance Gemspec/RequireMFA cop autocorrect to insert MFA directive after last metadata assignment

It's a little bit annoying that the `Gemspec/RequireMFA`' cop autocorrection
inserts MFA directive at the end, even if I grouped all `metadata=` assignments
in one place.

This patch tries to find the last `metadata = { ... }` or `metadata[]=` assignment
and inserts `spec.metadata['rubygems_mfa_required'] = 'true'` after this node.

Author: viralpraxis

changelog/new_enhance_gemspec_require_mfa_cop_autocorrect_to_insert_mfa_after_last_metadata_20250620024931.md

@@ -0,0 +1 @@
+* [#14314](https://github.com/rubocop/rubocop/pull/14314): Enhance `Gemspec/RequireMFA` cop autocorrect to insert MFA directive after last `metadata` assignment. ([@viralpraxis][])

lib/rubocop/cop/gemspec/require_mfa.rb

@@ -74,6 +74,14 @@ class RequireMFA < Base
           }
         PATTERN
 
+        # @!method metadata_assignment(node)
+        def_node_search :metadata_assignment, <<~PATTERN
+          `{
+            (send _ :metadata= _)
+            (send (send _ :metadata) :[]= (str _) _)
+          }
+        PATTERN
+
         # @!method rubygems_mfa_required(node)
         def_node_search :rubygems_mfa_required, <<~PATTERN
           (pair (str "rubygems_mfa_required") $_)
@@ -131,9 +139,15 @@ def correct_metadata(corrector, metadata)
         end
 
         def insert_mfa_required(corrector, node, block_var)
-          corrector.insert_before(node.loc.end, <<~RUBY)
+          require_mfa_directive = <<~RUBY.strip
             #{block_var}.metadata['rubygems_mfa_required'] = 'true'
           RUBY
+
+          if (last_assignment = metadata_assignment(processed_source.ast).to_a.last)
+            corrector.insert_after(last_assignment, "\n#{require_mfa_directive}")
+          else
+            corrector.insert_before(node.loc.end, "#{require_mfa_directive}\n")
+          end
         end
 
         def change_value(corrector, value)

spec/rubocop/cop/gemspec/require_mfa_spec.rb

@@ -121,6 +121,26 @@
           end
         RUBY
       end
+
+      context 'when `metadata` assignment is not the last one' do
+        it 'registers an offense' do
+          expect_offense(<<~RUBY, 'my.gemspec')
+            Gem::Specification.new do |spec|
+            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `metadata['rubygems_mfa_required']` must be set to `'true'`.
+              spec.metadata['foo'] = 'bar'
+              spec.author = 'viralpraxis'
+            end
+          RUBY
+
+          expect_correction(<<~RUBY)
+            Gem::Specification.new do |spec|
+              spec.metadata['foo'] = 'bar'
+            spec.metadata['rubygems_mfa_required'] = 'true'
+              spec.author = 'viralpraxis'
+            end
+          RUBY
+        end
+      end
     end
   end