1 files changed, 77 insertions, 0 deletions
diff --git a/rubocop/cop/avoid_return_from_blocks.rb b/rubocop/cop/avoid_return_from_blocks.rb
new file mode 100644
index 00000000000..40b2aed019f
--- /dev/null
+++ b/rubocop/cop/avoid_return_from_blocks.rb
@@ -0,0 +1,77 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    # Checks for return inside blocks.
+    # For more information see: https://gitlab.com/gitlab-org/gitlab-ce/issues/42889
+    #
+    # @example
+    #   # bad
+    #   call do
+    #     return if something
+    #
+    #     do_something_else
+    #   end
+    #
+    #   # good
+    #   call do
+    #     break if something
+    #
+    #     do_something_else
+    #   end
+    #
+    class AvoidReturnFromBlocks < RuboCop::Cop::Cop
+      MSG = 'Do not return from a block, use next or break instead.'
+      DEF_METHODS = %i[define_method lambda].freeze
+      WHITELISTED_METHODS = %i[each each_filename times loop].freeze
+
+      def on_block(node)
+        block_body = node.body
+
+        return unless block_body
+        return unless top_block?(node)
+
+        block_body.each_node(:return) do |return_node|
+          next if parent_blocks(node, return_node).all?(&method(:whitelisted?))
+
+          add_offense(return_node)
+        end
+      end
+
+      private
+
+      def top_block?(node)
+        current_node = node
+        top_block = nil
+
+        while current_node && current_node.type != :def
+          top_block = current_node if current_node.type == :block
+          current_node = current_node.parent
+        end
+
+        top_block == node
+      end
+
+      def parent_blocks(node, current_node)
+        blocks = []
+
+        until node == current_node || def?(current_node)
+          blocks << current_node if current_node.type == :block
+          current_node = current_node.parent
+        end
+
+        blocks << node if node == current_node && !def?(node)
+        blocks
+      end
+
+      def def?(node)
+        node.type == :def || node.type == :defs ||
+          (node.type == :block && DEF_METHODS.include?(node.method_name))
+      end
+
+      def whitelisted?(block_node)
+        WHITELISTED_METHODS.include?(block_node.method_name)
+      end
+    end
+  end
+end