Fix add_foreign_key with if_not_exists referencing the same table but via different columns

Author: fatkodima

activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb

@@ -1118,7 +1118,7 @@ def foreign_keys(table_name)
       #   +:deferred+ or +:immediate+ to specify the default behavior. Defaults to +false+.
       def add_foreign_key(from_table, to_table, **options)
         return unless use_foreign_keys?
-        return if options[:if_not_exists] == true && foreign_key_exists?(from_table, to_table)
+        return if options[:if_not_exists] == true && foreign_key_exists?(from_table, to_table, **options.slice(:column))
 
         options = foreign_key_options(from_table, to_table, options)
         at = create_alter_table from_table

activerecord/test/cases/migration/foreign_key_test.rb

@@ -185,6 +185,7 @@ class Astronaut < ActiveRecord::Base
           @connection.create_table "astronauts", force: true do |t|
             t.string :name
             t.references :rocket
+            t.references :favorite_rocket
           end
         end
 
@@ -233,6 +234,16 @@ def test_add_foreign_key_with_column
           assert_equal "fk_rails_78146ddd2e", fk.name unless current_adapter?(:SQLite3Adapter)
         end
 
+        def test_add_foreign_key_with_if_not_exists_to_already_referenced_table
+          @connection.add_foreign_key :astronauts, :rockets
+          @connection.add_foreign_key :astronauts, :rockets, column: "favorite_rocket_id", if_not_exists: true
+
+          foreign_keys = @connection.foreign_keys("astronauts")
+          assert_equal 2, foreign_keys.size
+          assert foreign_keys.all? { |fk| fk.to_table == "rockets" }
+          assert_equal ["favorite_rocket_id", "rocket_id"], foreign_keys.map(&:column).sort
+        end
+
         def test_add_foreign_key_with_non_standard_primary_key
           @connection.create_table :space_shuttles, id: false, force: true do |t|
             t.bigint :pk, primary_key: true