[Fix rubocop#787] Make Rails/Pluck aware of all keys

Fixes rubocop#787.

This PR makes `Rails/Pluck` aware of all keys.

Author: koic

changelog/change_make_rails_pluck_aware_of_all_keys.md

@@ -0,0 +1 @@
+* [#787](https://github.com/rubocop/rubocop-rails/issues/787): Make `Rails/Pluck` aware of all keys. ([@koic][])

lib/rubocop/cop/rails/pluck.rb

@@ -21,27 +21,28 @@ class Pluck < Base
         extend AutoCorrector
         extend TargetRailsVersion
 
-        MSG = 'Prefer `pluck(:%<value>s)` over `%<current>s`.'
+        MSG = 'Prefer `%<replacement>s` over `%<current>s`.'
 
         minimum_target_rails_version 5.0
 
         def_node_matcher :pluck_candidate?, <<~PATTERN
-          ({block numblock} (send _ {:map :collect}) $_argument (send (lvar $_element) :[] (sym $_value)))
+          ({block numblock} (send _ {:map :collect}) $_argument (send (lvar $_element) :[] $_key))
         PATTERN
 
         def on_block(node)
-          pluck_candidate?(node) do |argument, element, value|
+          pluck_candidate?(node) do |argument, element, key|
             match = if node.block_type?
                       argument.children.first.source.to_sym == element
                     else # numblock
                       argument == 1 && element == :_1
                     end
             next unless match
 
-            message = message(value, node)
+            replacement = "pluck(#{key.source})"
+            message = message(replacement, node)
 
             add_offense(offense_range(node), message: message) do |corrector|
-              corrector.replace(offense_range(node), "pluck(:#{value})")
+              corrector.replace(offense_range(node), replacement)
             end
           end
         end
@@ -53,10 +54,10 @@ def offense_range(node)
           node.send_node.loc.selector.join(node.loc.end)
         end
 
-        def message(value, node)
+        def message(replacement, node)
           current = offense_range(node).source
 
-          format(MSG, value: value, current: current)
+          format(MSG, replacement: replacement, current: current)
         end
       end
     end

spec/rubocop/cop/rails/pluck_spec.rb

@@ -3,7 +3,7 @@
 RSpec.describe RuboCop::Cop::Rails::Pluck, :config do
   %w[map collect].each do |method|
     context 'when using Rails 5.0 or newer', :rails50 do
-      context "when `#{method}` can be replaced with `pluck`" do
+      context "when `#{method}` with symbol literal key can be replaced with `pluck`" do
         it 'registers an offense' do
           expect_offense(<<~RUBY, method: method)
             x.%{method} { |a| a[:foo] }
@@ -16,18 +16,36 @@
         end
       end
 
-      context 'when the block argument is unused' do
-        it 'does not register an offense' do
-          expect_no_offenses(<<~RUBY)
-            x.#{method} { |a| b[:foo] }
+      context "when `#{method}` with string literal key can be replaced with `pluck`" do
+        it 'registers an offense' do
+          expect_offense(<<~RUBY, method: method)
+            x.%{method} { |a| a['foo'] }
+              ^{method}^^^^^^^^^^^^^^^^^ Prefer `pluck('foo')` over `%{method} { |a| a['foo'] }`.
+          RUBY
+
+          expect_correction(<<~RUBY)
+            x.pluck('foo')
+          RUBY
+        end
+      end
+
+      context "when `#{method}` with method call key can be replaced with `pluck`" do
+        it 'registers an offense' do
+          expect_offense(<<~RUBY, method: method)
+            x.%{method} { |a| a[obj.do_something] }
+              ^{method}^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer `pluck(obj.do_something)` over `%{method} { |a| a[obj.do_something] }`.
+          RUBY
+
+          expect_correction(<<~RUBY)
+            x.pluck(obj.do_something)
           RUBY
         end
       end
 
-      context 'when the value is not a symbol' do
+      context 'when the block argument is unused' do
         it 'does not register an offense' do
           expect_no_offenses(<<~RUBY)
-            x.#{method} { |a| a['foo'] }
+            x.#{method} { |a| b[:foo] }
           RUBY
         end
       end