Add any object that repsonds to to_s to the DOM in Arbre blocks.

Before this commit:

  index do
    column("My Column"){ 1 }
  end

Would result in an empty column. Now the object is appended to the DOM
and will result in a colum of "1"s.

The return value is ignored if the user has already appended other
elements to the DOM. This might trip up some users, however it is more
likely that you are either going to build up a DOM structure or return a
simple value, not both.

Thanks for the pull requests from @bobbytables and @utkarshkukreti

References isses activeadmin#470, 154

Author: gregbell

lib/active_admin/arbre/builder.rb

@@ -65,7 +65,7 @@ def build_tag(klass, *args, &block)
           # Render the blocks contents
           if block_given?
             with_current_dom_context tag do
-              insert_text_node_if_string(yield)
+              append_return_block(yield)
             end
           end
         end
@@ -98,10 +98,13 @@ def with_current_dom_context(tag)
       end
       alias_method :within, :with_current_dom_context
 
-      # Inserts a text node if the tag is a string
-      def insert_text_node_if_string(tag)
-        if tag.is_a?(String)
-          current_dom_context << Arbre::HTML::TextNode.from_string(tag)
+      # Appends the value to the current DOM element if there are no
+      # existing DOM Children and it responds to #to_s
+      def append_return_block(tag)
+        return nil if current_dom_context.children.any?
+
+        if !tag.is_a?(Arbre::HTML::Element) && tag.respond_to?(:to_s)
+          current_dom_context << Arbre::HTML::TextNode.from_string(tag.to_s)
         end
       end
     end

lib/active_admin/arbre/html/element.rb

@@ -35,7 +35,7 @@ def tag_name
 
       def build(*args, &block)
         # Render the block passing ourselves in
-        insert_text_node_if_string(block.call(self)) if block
+        append_return_block(block.call(self)) if block
       end
 
       def add_child(child)

spec/unit/arbre/html_spec.rb

@@ -131,12 +131,22 @@
     item.parent.should == list
   end
 
-  it "should set a string content return value with no children" do
-    li do
-      "Hello World"
-    end.to_s.should == <<-HTML
-<li>Hello World</li>
-HTML
+
+  ["Hello World", 1, 1.5].each do |value|
+    it "should append the return value of '#{value}' when no other children added to the DOM" do
+      li do
+        value
+      end.to_s.should == "<li>#{value}</li>\n"
+    end
+  end
+
+  ["Hello World", 1, 1.5].each do |value|
+    it "should not append the return value of '#{value}' when children have been added to the DOM" do
+      li do
+        text_node("Already Added")
+        value
+      end.to_s.should == "<li>Already Added</li>\n"
+    end
   end
 
   describe "text nodes" do