1 files changed, 121 insertions, 0 deletions
diff --git a/rubocop/cop/migration/add_limit_to_text_columns.rb b/rubocop/cop/migration/add_limit_to_text_columns.rb
new file mode 100644
index 00000000000..15c28bb9266
--- /dev/null
+++ b/rubocop/cop/migration/add_limit_to_text_columns.rb
@@ -0,0 +1,121 @@
+# frozen_string_literal: true
+
+require_relative '../../migration_helpers'
+
+module RuboCop
+  module Cop
+    module Migration
+      # Cop that enforces always adding a limit on text columns
+      class AddLimitToTextColumns < RuboCop::Cop::Cop
+        include MigrationHelpers
+
+        MSG = 'Text columns should always have a limit set (255 is suggested). ' \
+          'You can add a limit to a `text` column by using `add_text_limit`'.freeze
+
+        def_node_matcher :reverting?, <<~PATTERN
+          (def :down ...)
+        PATTERN
+
+        def_node_matcher :add_text_limit?, <<~PATTERN
+          (send _ :add_text_limit ...)
+        PATTERN
+
+        def on_def(node)
+          return unless in_migration?(node)
+
+          # Don't enforce the rule when on down to keep consistency with existing schema
+          return if reverting?(node)
+
+          node.each_descendant(:send) do |send_node|
+            next unless text_operation?(send_node)
+
+            # We require a limit for the same table and attribute name
+            if text_limit_missing?(node, *table_and_attribute_name(send_node))
+              add_offense(send_node, location: :selector)
+            end
+          end
+        end
+
+        private
+
+        def text_operation?(node)
+          modifier = node.children[0]
+          migration_method = node.children[1]
+
+          if migration_method == :text
+            modifier.type == :lvar
+          elsif ADD_COLUMN_METHODS.include?(migration_method)
+            modifier.nil? && text_column?(node.children[4])
+          end
+        end
+
+        def text_column?(column_type)
+          column_type.type == :sym && column_type.value == :text
+        end
+
+        # For a given node, find the table and attribute this node is for
+        #
+        # Simple when we have calls to `add_column_XXX` helper methods
+        #
+        # A little bit more tricky when we have attributes defined as part of
+        # a create/change table block:
+        # - The attribute name is available on the node
+        # - Finding the table name requires to:
+        #   * go up
+        #   * find the first block the attribute def is part of
+        #   * go back down to find the create_table node
+        #   * fetch the table name from that node
+        def table_and_attribute_name(node)
+          migration_method = node.children[1]
+          table_name, attribute_name = ''
+
+          if migration_method == :text
+            # We are inside a node in a create/change table block
+            block_node = node.each_ancestor(:block).first
+            create_table_node = block_node
+                                  .children
+                                  .find { |n| TABLE_METHODS.include?(n.children[1])}
+
+            if create_table_node
+              table_name = create_table_node.children[2].value
+            else
+              # Guard against errors when a new table create/change migration
+              # helper is introduced and warn the author so that it can be
+              # added in TABLE_METHODS
+              table_name = 'unknown'
+              add_offense(block_node, message: 'Unknown table create/change helper')
+            end
+
+            attribute_name = node.children[2].value
+          else
+            # We are in a node for one of the ADD_COLUMN_METHODS
+            table_name = node.children[2].value
+            attribute_name = node.children[3].value
+          end
+
+          [table_name, attribute_name]
+        end
+
+        # Check if there is an `add_text_limit` call for the provided
+        # table and attribute name
+        def text_limit_missing?(node, table_name, attribute_name)
+          limit_found = false
+
+          node.each_descendant(:send) do |send_node|
+            next unless add_text_limit?(send_node)
+
+            limit_table = send_node.children[2].value
+            limit_attribute = send_node.children[3].value
+
+            if limit_table == table_name && limit_attribute == attribute_name
+              limit_found = true
+              break
+            end
+          end
+
+          !limit_found
+        end
+      end
+    end
+  end
+end