Include blank attributes in HTML output (#517)

This is mostly a full revert of commit 1526789 which was a bad change. Empty attributes are valid HTML and should be supported in Arbre (e.g. boolean attributes). The bad commit was for just addressing the class attribute but that applied to any attribute in HTML when it shouldn't have, even for class.

lib/arbre/html/attributes.rb

@@ -6,13 +6,12 @@ class Attributes < Hash
 
       def to_s
         flatten_hash.map do |name, value|
-          next if value_empty?(value)
-          "#{html_escape(name)}=\"#{html_escape(value)}\""
-        end.compact.join ' '
-      end
-
-      def any?
-        super{ |k,v| !value_empty?(v) }
+          if value.nil?
+            html_escape(name)
+          else
+            "#{html_escape(name)}=\"#{html_escape(value)}\""
+          end
+        end.join ' '
       end
 
       protected
@@ -29,10 +28,6 @@ def flatten_hash(hash = self, old_path = [], accumulator = {})
         accumulator
       end
 
-      def value_empty?(value)
-        value.respond_to?(:empty?) ? value.empty? : !value
-      end
-
       def html_escape(s)
         ERB::Util.html_escape(s)
       end

lib/arbre/html/tag.rb

@@ -150,7 +150,7 @@ def child_is_text?
       end
 
       def attributes_html
-        " #{attributes}" if attributes.any?
+        attributes.any? ? " " + attributes.to_s : nil
       end
 
       def set_for_attribute(record)

spec/arbre/unit/html/tag_attributes_spec.rb

@@ -18,12 +18,12 @@
         expect(tag.to_s).to eq "<tag id=\"my_id\"></tag>\n"
       end
 
-      it "shouldn't render attributes that are empty" do
+      it "should still render attributes that are empty" do
         tag.class_list # initializes an empty ClassList
         tag.set_attribute :foo, ''
         tag.set_attribute :bar, nil
 
-        expect(tag.to_s).to eq "<tag id=\"my_id\"></tag>\n"
+        expect(tag.to_s).to eq "<tag id=\"my_id\" class=\"\" foo=\"\" bar></tag>\n"
       end
 
       context "with hyphenated attributes" do
@@ -41,12 +41,12 @@
           expect(tag.to_s).to eq "<tag id=\"my_id\" data-action=\"some_action\"></tag>\n"
         end
 
-        it "shouldn't render attributes that are empty" do
+        it "should still render attributes that are empty" do
           tag.class_list # initializes an empty ClassList
           tag.set_attribute :foo, { bar: '' }
           tag.set_attribute :bar, { baz: nil }
 
-          expect(tag.to_s).to eq "<tag id=\"my_id\" data-action=\"some_action\"></tag>\n"
+          expect(tag.to_s).to eq "<tag id=\"my_id\" data-action=\"some_action\" class=\"\" foo-bar=\"\" bar-baz></tag>\n"
         end
       end