Include empty attributes in HTML output (#543)

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. Note that if an attribute value is nil then it is removed. This follows similar output logic to Rails `tag.attributes` helper.

lib/arbre/html/attributes.rb

@@ -5,16 +5,11 @@ module HTML
     class Attributes < Hash
 
       def to_s
-        flatten_hash.map do |name, value|
-          next if value_empty?(value)
+        flatten_hash.compact.map do |name, value|
           "#{html_escape(name)}=\"#{html_escape(value)}\""
         end.compact.join ' '
       end
 
-      def any?
-        super{ |k,v| !value_empty?(v) }
-      end
-
       protected
 
       def flatten_hash(hash = self, old_path = [], accumulator = {})
@@ -29,10 +24,6 @@ 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

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 but not nil" 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=\"\"></tag>\n"
       end
 
       context "with hyphenated attributes" do
@@ -41,28 +41,28 @@
           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 but not nil" 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=\"\"></tag>\n"
         end
       end
 
       context "when there is a deeply nested attribute" do
-        before { tag.build id: "my_id", foo: { bar: { baz: 'foozle' } } }
+        before { tag.build id: "my_id", foo: { bar: { bat: nil, baz: 'foozle' } } }
 
         it "should flatten the attributes when rendering to html" do
           expect(tag.to_s).to eq "<tag id=\"my_id\" foo-bar-baz=\"foozle\"></tag>\n"
         end
       end
 
       context "when there are multiple nested attributes" do
-        before { tag.build id: "my_id", foo: { bar: 'foozle1', baz: 'foozle2' } }
+        before { tag.build id: "my_id", foo: { bar: 'foozle1', bat: nil, baz: '' } }
 
         it "should flatten the attributes when rendering to html" do
-          expect(tag.to_s).to eq "<tag id=\"my_id\" foo-bar=\"foozle1\" foo-baz=\"foozle2\"></tag>\n"
+          expect(tag.to_s).to eq "<tag id=\"my_id\" foo-bar=\"foozle1\" foo-baz=\"\"></tag>\n"
         end
       end
     end