[Fix #578] Add Rails/RedundantPresenceValidationOnBelongsTo cop

changelog/new_redundant_presence_validation_for_required_belongs_to_association_cop.md

@@ -0,0 +1 @@
+* [#594](https://github.com/rubocop/rubocop-rails/pull/594): Add `Rails/RedundantPresenceValidationOnBelongsTo` cop. ([@pirj][])

config/default.yml

@@ -618,6 +618,11 @@ Rails/RedundantForeignKey:
   Enabled: true
   VersionAdded: '2.6'
 
+Rails/RedundantPresenceValidationOnBelongsTo:
+  Description: 'Checks for redundant presence validation on belongs_to association.'
+  Enabled: pending
+  VersionAdded: '<<next>>'
+
 Rails/RedundantReceiverInWithOptions:
   Description: 'Checks for redundant receiver in `with_options`.'
   Enabled: true

lib/rubocop/cop/rails/redundant_presence_validation_on_belongs_to.rb

@@ -0,0 +1,192 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Rails
+      # Since Rails 5.0 the default for `belongs_to` is `optional: false`
+      # unless `config.active_record.belongs_to_required_by_default` is
+      # explicitly set to `false`. The presence validator is added
+      # automatically, and explicit presence validation is redundant.
+      #
+      # @example
+      #   # bad
+      #   belongs_to :user
+      #   validates :user, presence: true
+      #
+      #   # bad
+      #   belongs_to :user
+      #   validates :user_id, presence: true
+      #
+      #   # bad
+      #   belongs_to :author, foreign_key: :user_id
+      #   validates :user_id, presence: true
+      #
+      #   # good
+      #   belongs_to :user
+      #
+      #   # good
+      #   belongs_to :author, foreign_key: :user_id
+      #
+      class RedundantPresenceValidationOnBelongsTo < Base
+        include RangeHelp
+        extend AutoCorrector
+        extend TargetRailsVersion
+
+        MSG = 'Remove explicit presence validation for `%<association>s`.'
+        RESTRICT_ON_SEND = %i[validates].freeze
+
+        minimum_target_rails_version 5.0
+
+        # @!method presence_validation?(node)
+        #   Match a `validates` statement with a presence check
+        #
+        #   @example source that matches - by association
+        #     validates :user, presence: true
+        #
+        #   @example source that matches - with presence options
+        #     validates :user, presence: { message: 'duplicate' }
+        #
+        #   @example source that matches - by a foreign key
+        #     validates :user_id, presence: true
+        def_node_matcher :presence_validation?, <<~PATTERN
+          $(
+            send nil? :validates
+            (sym $_)
+            ...
+            $(hash <$(pair (sym :presence) {true hash}) ...>)
+          )
+        PATTERN
+
+        # @!method optional_option?(node)
+        #  Match a `belongs_to` association with an optional option in a hash
+        def_node_matcher :optional?, <<~PATTERN
+          (send nil? :belongs_to _ ... #optional_option?)
+        PATTERN
+
+        # @!method optional_option?(node)
+        #  Match an optional option in a hash
+        def_node_matcher :optional_option?, <<~PATTERN
+          {
+            (hash <(pair (sym :optional) true) ...>)   # optional: true
+            (hash <(pair (sym :required) false) ...>)  # required: false
+          }
+        PATTERN
+
+        # @!method any_belongs_to?(node, association:)
+        #   Match a class with `belongs_to` with no regard to `foreign_key` option
+        #
+        #   @example source that matches
+        #     belongs_to :user
+        #
+        #   @example source that matches - regardless of `foreign_key`
+        #     belongs_to :author, foreign_key: :user_id
+        #
+        #   @param node [RuboCop::AST::Node]
+        #   @param association [Symbol]
+        #   @return [Array<RuboCop::AST::Node>, nil] matching node
+        def_node_matcher :any_belongs_to?, <<~PATTERN
+          (begin
+            <
+              $(send nil? :belongs_to (sym %association) ...)
+              ...
+            >
+          )
+        PATTERN
+
+        # @!method belongs_to?(node, key:, fk:)
+        #   Match a class with a matching association, either by name or an explicit
+        #   `foreign_key` option
+        #
+        #   @example source that matches - fk matches `foreign_key` option
+        #     belongs_to :author, foreign_key: :user_id
+        #
+        #   @example source that matches - key matches association name
+        #     belongs_to :user
+        #
+        #   @example source that does not match - explicit `foreign_key` does not match
+        #     belongs_to :user, foreign_key: :account_id
+        #
+        #   @param node [RuboCop::AST::Node]
+        #   @param key [Symbol] e.g. `:user`
+        #   @param fk [Symbol] e.g. `:user_id`
+        #   @return [Array<RuboCop::AST::Node>] matching nodes
+        def_node_matcher :belongs_to?, <<~PATTERN
+          (begin
+            <
+              ${
+                #belongs_to_without_fk?(%key)         # belongs_to :user
+                #belongs_to_with_a_matching_fk?(%fk)  # belongs_to :author, foreign_key: :user_id
+              }
+              ...
+            >
+          )
+        PATTERN
+
+        # @!method belongs_to_without_fk?(node, fk)
+        #   Match a matching `belongs_to` association, without an explicit `foreign_key` option
+        #
+        #   @param node [RuboCop::AST::Node]
+        #   @param key [Symbol] e.g. `:user`
+        #   @return [Array<RuboCop::AST::Node>] matching nodes
+        def_node_matcher :belongs_to_without_fk?, <<~PATTERN
+          {
+            (send nil? :belongs_to (sym %1))        # belongs_to :user
+            (send nil? :belongs_to (sym %1) !hash)  # belongs_to :user, -> { not_deleted }
+            (send nil? :belongs_to (sym %1) !(hash <(pair (sym :foreign_key) _) ...>))
+          }
+        PATTERN
+
+        # @!method belongs_to_with_a_matching_fk?(node, fk)
+        #   Match a matching `belongs_to` association with a matching explicit `foreign_key` option
+        #
+        #   @example source that matches
+        #     belongs_to :author, foreign_key: :user_id
+        #
+        #   @param node [RuboCop::AST::Node]
+        #   @param fk [Symbol] e.g. `:user_id`
+        #   @return [Array<RuboCop::AST::Node>] matching nodes
+        def_node_matcher :belongs_to_with_a_matching_fk?, <<~PATTERN
+          (send nil? :belongs_to ... (hash <(pair (sym :foreign_key) (sym %1)) ...>))
+        PATTERN
+
+        def on_send(node)
+          validation, key, options, presence = presence_validation?(node)
+          return unless validation
+
+          belongs_to = belongs_to_for(node.parent, key)
+          return unless belongs_to
+          return if optional?(belongs_to)
+
+          message = format(MSG, association: key.to_s)
+
+          add_offense(presence, message: message) do |corrector|
+            remove_presence_validation(corrector, node, options, presence)
+          end
+        end
+
+        private
+
+        def belongs_to_for(model_class_node, key)
+          if key.to_s.end_with?('_id')
+            normalized_key = key.to_s.delete_suffix('_id').to_sym
+            belongs_to?(model_class_node, key: normalized_key, fk: key)
+          else
+            any_belongs_to?(model_class_node, association: key)
+          end
+        end
+
+        def remove_presence_validation(corrector, node, options, presence)
+          if options.children.one?
+            corrector.remove(range_by_whole_lines(node.source_range, include_final_newline: true))
+          else
+            range = range_with_surrounding_comma(
+              range_with_surrounding_space(range: presence.source_range, side: :left),
+              :left
+            )
+            corrector.remove(range)
+          end
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rails_cops.rb

@@ -73,6 +73,7 @@
 require_relative 'rails/read_write_attribute'
 require_relative 'rails/redundant_allow_nil'
 require_relative 'rails/redundant_foreign_key'
+require_relative 'rails/redundant_presence_validation_on_belongs_to'
 require_relative 'rails/redundant_receiver_in_with_options'
 require_relative 'rails/redundant_travel_back'
 require_relative 'rails/reflection_class_name'