Also check duplicated mixins in shims and TODO files

lib/tapioca/helpers/rbi_files_helper.rb

@@ -178,6 +178,9 @@ def shims_or_todos_have_duplicates?(nodes, shim_rbi_dir:, todo_rbi_file:)
       shims_or_todos_empty_scopes = extract_empty_scopes(shims_or_todos)
       return true unless shims_or_todos_empty_scopes.empty?
 
+      mixins = extract_mixins(shims_or_todos)
+      return true unless mixins.empty?
+
       props = extract_methods_and_attrs(shims_or_todos)
       return false if props.empty?
 
@@ -215,6 +218,13 @@ def extract_methods_and_attrs(nodes)
       end, T::Array[T.any(RBI::Method, RBI::Attr)])
     end
 
+    sig { params(nodes: T::Array[RBI::Node]).returns(T::Array[T.any(RBI::Mixin, RBI::RequiresAncestor)]) }
+    def extract_mixins(nodes)
+      T.cast(nodes.select do |node|
+        node.is_a?(RBI::Mixin) || node.is_a?(RBI::RequiresAncestor)
+      end, T::Array[T.all(RBI::Mixin, RBI::RequiresAncestor)])
+    end
+
     sig { params(nodes: T::Array[T.any(RBI::Method, RBI::Attr)]).returns(T::Array[T.any(RBI::Method, RBI::Attr)]) }
     def extract_nodes_with_sigs(nodes)
       nodes.reject { |node| node.sigs.empty? }

spec/tapioca/cli/check_shims_spec.rb

@@ -235,6 +235,73 @@ class Foo
           refute_success_status(result)
         end
 
+        it "detects duplicated includes and extends" do
+          @project.write("sorbet/rbi/gems/[email protected]", <<~RBI)
+            module Bar; end
+
+            class Foo
+              include Bar
+              extend Bar
+              mixes_in_class_methods Bar
+              requires_ancestor { Bar }
+            end
+
+            module Baz; end
+
+            class Qux
+              # RBI does not attempt to resolve constants used in the mixins, so if the constant duplicated in the shim
+              # does not use the same namespace, Tapioca won't catch it. The following lines won't raise duplication
+              # errors.
+              include Baz
+              extend Baz
+              mixes_in_class_methods Baz
+              requires_ancestor { Baz }
+            end
+          RBI
+
+          @project.write("sorbet/rbi/shims/foo.rbi", <<~RBI)
+            class Foo
+              include Bar
+              extend Bar
+              mixes_in_class_methods Bar
+              requires_ancestor { Bar }
+            end
+
+            class Qux
+              include ::Baz
+              extend ::Baz
+              mixes_in_class_methods ::Baz
+              requires_ancestor { ::Baz }
+            end
+          RBI
+
+          result = @project.tapioca("check-shims --no-payload")
+
+          assert_includes(result.err, <<~ERR)
+            Duplicated RBI for ::Foo.include(Bar):
+             * sorbet/rbi/shims/foo.rbi:2:2-2:13
+             * sorbet/rbi/gems/[email protected]:4:2-4:13
+
+            Duplicated RBI for ::Foo.extend(Bar):
+             * sorbet/rbi/shims/foo.rbi:3:2-3:12
+             * sorbet/rbi/gems/[email protected]:5:2-5:12
+
+            Duplicated RBI for ::Foo.mixes_in_class_method(Bar):
+             * sorbet/rbi/shims/foo.rbi:4:2-4:28
+             * sorbet/rbi/gems/[email protected]:6:2-6:28
+
+            Duplicated RBI for ::Foo.requires_ancestor(Bar):
+             * sorbet/rbi/shims/foo.rbi:5:2-5:27
+             * sorbet/rbi/gems/[email protected]:7:2-7:27
+          ERR
+
+          assert_includes(result.err, <<~ERR)
+            Please remove the duplicated definitions from sorbet/rbi/shims and sorbet/rbi/todo.rbi
+          ERR
+
+          refute_success_status(result)
+        end
+
         it "detects duplicates from same shim file" do
           @project.write("sorbet/rbi/gems/[email protected]", <<~RBI)
             class Foo