Raise helpful error block given to association

Closes #1033

> Arguably, association should raise and let the developer know
> they're using it in an unexpected way. I'd love to see a PR for
> that (with a test!), so if you're interested in contributing that,
> please do!
> https://github.com/thoughtbot/factory_girl/issues/1032#issuecomment-329297006

Co-authored-by: Daniel Colson <danieljamescolson@gmail.com>

lib/factory_bot/definition_proxy.rb

@@ -131,7 +131,15 @@ module FactoryBot
     #    name of the factory. For example, a "user" association will by
     #    default use the "user" factory.
     def association(name, *options)
-      @definition.declare_attribute(Declaration::Association.new(name, *options))
+      if block_given?
+        raise AssociationDefinitionError.new(
+          "Unexpected block passed to '#{name}' association "\
+          "in '#{@definition.name}' factory",
+        )
+      else
+        declaration = Declaration::Association.new(name, *options)
+        @definition.declare_attribute(declaration)
+      end
     end
 
     def to_create(&block)

lib/factory_bot/errors.rb

@@ -14,6 +14,9 @@ module FactoryBot
   # Raised when defining an attribute twice in the same factory
   class AttributeDefinitionError < RuntimeError; end
 
+  # Raised when attempting to pass a block to an association definition
+  class AssociationDefinitionError < RuntimeError; end
+
   # Raised when a method is defined in a factory or trait with arguments
   class MethodDefinitionError < RuntimeError; end
 

spec/factory_bot/definition_proxy_spec.rb

@@ -131,19 +131,37 @@ describe FactoryBot::DefinitionProxy, "#sequence" do
 end
 
 describe FactoryBot::DefinitionProxy, "#association" do
-  subject     { FactoryBot::Definition.new(:name) }
-  let(:proxy) { FactoryBot::DefinitionProxy.new(subject) }
-
   it "declares an association" do
+    definition = FactoryBot::Definition.new(:definition_name)
+    proxy = FactoryBot::DefinitionProxy.new(definition)
+
     proxy.association(:association_name)
-    expect(subject).to have_association_declaration(:association_name)
+
+    expect(definition).to have_association_declaration(:association_name)
   end
 
   it "declares an association with options" do
+    definition = FactoryBot::Definition.new(:definition_name)
+    proxy = FactoryBot::DefinitionProxy.new(definition)
+
     proxy.association(:association_name, name: "Awesome")
-    expect(subject).to have_association_declaration(:association_name).
+
+    expect(definition).to have_association_declaration(:association_name).
       with_options(name: "Awesome")
   end
+
+  context "when passing a block" do
+    it "raises an error" do
+      definition = FactoryBot::Definition.new(:post)
+      proxy = FactoryBot::DefinitionProxy.new(definition)
+
+      expect { proxy.association(:author) {} }.
+        to raise_error(
+          FactoryBot::AssociationDefinitionError,
+          "Unexpected block passed to 'author' association in 'post' factory",
+        )
+    end
+  end
 end
 
 describe FactoryBot::DefinitionProxy, "adding callbacks" do