Rename internal `@saving` state to `@_saving`

Usually we add `_` prefix for newly added short term living (used)
internal state (e.g. ae02898, d1107f4, dcb8259), and also `@saving`
might be already used in users' code.

activerecord/CHANGELOG.md

@@ -1,7 +1,7 @@
-*   Prevent double saves in autosave of cyclic associations
+*   Prevent double saves in autosave of cyclic associations.
 
-    Adds a @saving state which tracks if a record is currently being saved.
-    If @saving is set to true, the record won't be saved by the autosave callbacks.
+    Adds an internal saving state which tracks if a record is currently being saved.
+    If a state is set to true, the record won't be saved by the autosave callbacks.
 
     *Petrik de Heus*
 

activerecord/lib/active_record/autosave_association.rb

@@ -233,9 +233,9 @@ module ActiveRecord
 
     # Reloads the attributes of the object as usual and clears <tt>marked_for_destruction</tt> flag.
     def reload(options = nil)
+      @_saving = false
       @marked_for_destruction = false
       @destroyed_by_association = nil
-      @saving = false
       super
     end
 
@@ -284,17 +284,17 @@ module ActiveRecord
 
     protected
       def _can_save? # :nodoc:
-        !destroyed? && !@saving
+        !destroyed? && !@_saving
       end
 
     private
       # Track if this record is being saved. If it is being saved we
       # can skip saving it in the autosave callbacks.
       def _saving
-        previously_saving, @saving = @saving, true
+        previously_saving, @_saving = @_saving, true
         yield
       ensure
-        @saving = previously_saving
+        @_saving = previously_saving
       end
 
       # Returns the record for an association collection that should be validated

activerecord/lib/active_record/core.rb

@@ -825,8 +825,8 @@ module ActiveRecord
         @readonly                 = false
         @previously_new_record    = false
         @destroyed                = false
+        @_saving                  = false
         @marked_for_destruction   = false
-        @saving                   = false
         @destroyed_by_association = nil
         @_start_transaction_state = nil
         @strict_loading           = self.class.strict_loading_by_default

activerecord/lib/active_record/transactions.rb

@@ -404,7 +404,7 @@ module ActiveRecord
               attr = attr.with_value_from_user(value) if attr.value != value
               attr
             end
-            @saving = false
+            @_saving = false
             @mutations_from_database = nil
             @mutations_before_last_save = nil
             if @attributes.fetch_value(@primary_key) != restore_state[:id]

activerecord/test/cases/autosave_association_test.rb

@@ -1996,15 +1996,15 @@ class TestCyclicAutosaveAssociationsOnlySaveOnce < ActiveRecord::TestCase
     child = Ship.new(name: "Nights Dirty Lightning")
     child.build_pirate
     assert_not child.save
-    assert_not child.instance_variable_get(:@saving)
+    assert_not child.instance_variable_get(:@_saving)
   end
 
   test "saving? is set to false after multiple nested saves" do
     autosave_saving_stack = []
 
     ship_with_saving_stack = Class.new(Ship) do
-      before_save { autosave_saving_stack << @saving }
-      after_save  { autosave_saving_stack << @saving }
+      before_save { autosave_saving_stack << @_saving }
+      after_save  { autosave_saving_stack << @_saving }
     end
 
     pirate_with_callbacks = Class.new(Pirate) do
@@ -2017,6 +2017,6 @@ class TestCyclicAutosaveAssociationsOnlySaveOnce < ActiveRecord::TestCase
     child.pirate = pirate_with_callbacks.new(catchphrase: "Aye")
     child.save!
     assert_equal [true] * 8, autosave_saving_stack
-    assert_not child.instance_variable_get(:@saving)
+    assert_not child.instance_variable_get(:@_saving)
   end
 end