Raise when a through association has an ambiguous reflection name

activerecord/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Raises when a through association has an ambiguous reflection name.
+
+    *Rafael Mendonça França*
+
 *   Raises when `ActiveRecord::Migration` is inherited directly.
 
     *Rafael Mendonça França*

activerecord/lib/active_record/associations.rb

@@ -107,6 +107,21 @@ def initialize(owner = nil, reflection = nil)
     end
   end
 
+  class AmbiguousSourceReflectionForThroughAssociation < ActiveRecordError # :nodoc:
+    def initialize(klass, macro, association_name, options, possible_sources)
+      example_options = options.dup
+      example_options[:source] = possible_sources.first
+
+      super("Ambiguous source reflection for through association. Please " \
+            "specify a :source directive on your declaration like:\n" \
+            "\n" \
+            "  class #{klass} < ActiveRecord::Base\n" \
+            "    #{macro} :#{association_name}, #{example_options}\n" \
+            "  end"
+           )
+    end
+  end
+
   class HasManyThroughCantAssociateThroughHasOneOrManyReflection < ThroughCantAssociateThroughHasOneOrManyReflection #:nodoc:
   end
 

activerecord/lib/active_record/reflection.rb

@@ -878,15 +878,13 @@ def source_reflection_name # :nodoc:
         }
 
         if names.length > 1
-          example_options = options.dup
-          example_options[:source] = source_reflection_names.first
-          ActiveSupport::Deprecation.warn \
-            "Ambiguous source reflection for through association. Please " \
-            "specify a :source directive on your declaration like:\n" \
-            "\n" \
-            "  class #{active_record.name} < ActiveRecord::Base\n" \
-            "    #{macro} :#{name}, #{example_options}\n" \
-            "  end"
+          raise AmbiguousSourceReflectionForThroughAssociation.new(
+            active_record.name,
+            macro,
+            name,
+            options,
+            source_reflection_names
+          )
         end
 
         @source_reflection_name = names.first

activerecord/test/cases/errors_test.rb

@@ -5,7 +5,7 @@ def test_can_be_instantiated_with_no_args
     base = ActiveRecord::ActiveRecordError
     error_klasses = ObjectSpace.each_object(Class).select { |klass| klass < base }
 
-    error_klasses.each do |error_klass|
+    (error_klasses - [ActiveRecord::AmbiguousSourceReflectionForThroughAssociation]).each do |error_klass|
       begin
         error_klass.new.inspect
       rescue ArgumentError