short form for dynamic attributes

Author: loomchild

README.md

@@ -46,6 +46,34 @@ is equivalent to:
 > [!TIP]  
 > Computed attributes work with partials as well as standard HTML tags.
 
+#### Short form
+
+If value of a dynamic attribute is the same as its name, you can omit the value.
+
+For example
+```html
+<div style%>Text</div>
+```
+is equivalent to:
+```erb
+<div style%="style">Text</div>
+```
+which in turn is equivalent to:
+```erb
+<div style="<%= style %>">Text</div>
+```
+
+Since `class` is a Ruby keyword, it's treated specially:
+```html
+<div class%>Text</div>
+```
+is equivalent to:
+```erb
+<div class="<%= binding.local_variable_get('class') %>">Text</div>
+```
+
+> [!TIP]
+> Short form is especially useful when you want to apply a `class` and `style` attribute to a partial root.
 
 ### Partials
 

lib/theo-rails/theo.rb

@@ -1,9 +1,10 @@
 module Theo
   module Rails
-    ATTRIBUTE_NAME = /[\w\-:@]+/
+    ATTRIBUTE_NAME = /(?<name>[a-z][\w\-:@]*)/
     ATTRIBUTE_VALUE = /(?:(?:"(?<value>[^"]*)")|(?:'(?<value>[^']*)'))/
-    ATTRIBUTE = /(?:(?:(?<name>#{ATTRIBUTE_NAME.source})\s*=\s*#{ATTRIBUTE_VALUE.source})|(?<name>#{ATTRIBUTE_NAME.source}))/
-    DYNAMIC_ATTRIBUTE = /(?:(?<name>#{ATTRIBUTE_NAME.source})\s*%=\s*#{ATTRIBUTE_VALUE.source})/
+    ATTRIBUTE = /(?:(?:#{ATTRIBUTE_NAME.source}\s*=\s*#{ATTRIBUTE_VALUE.source})|#{ATTRIBUTE_NAME.source})/
+    DYNAMIC_ATTRIBUTE = /(?:(?:#{ATTRIBUTE_NAME.source}\s*%=\s*#{ATTRIBUTE_VALUE.source})|(?:#{ATTRIBUTE_NAME.source}%))/
+    RESERVED_ATTRIBUTE_NAME = %w[alias and begin break case class def do else elsif end ensure false for if in module next nil not or redo rescue retry return self super then true undef unless until when while yield].to_set
     ATTRIBUTES = /(?<attrs>(?:\s+#{ATTRIBUTE.source})*)/
     LITERAL_ATTRIBUTES = %i[path as yields collection].freeze
     PARTIAL_TAG = /(?<partial>_\w+)/
@@ -16,7 +17,16 @@ module Rails
     class Theo
       def process(source)
         # Attributes
-        source = source.gsub(DYNAMIC_ATTRIBUTE, '\k<name>="<%= \k<value> %>"')
+        source = source.gsub(DYNAMIC_ATTRIBUTE) do |_|
+          match = Regexp.last_match
+
+          name = match[:name]
+
+          # See https://island94.org/2024/06/rails-strict-locals-local_assigns-and-reserved-keywords for more info
+          value = match[:value] || (RESERVED_ATTRIBUTE_NAME.include?(name) ? "binding.local_variable_get('#{name}')" : name)
+
+          "#{name}=\"<%= #{value} %>\""
+        end
 
         # Partials
         source.gsub(TEMPLATE) do |_|

spec/theo-rails/theo_spec.rb

@@ -17,6 +17,18 @@
     include_examples 'theo to erb', 'evaluates dynamic attribute',
                      %(<a href%="2 % 2 == 0 ? '/even' : '/odd'">Link</a>),
                      %(<a href="<%= 2 % 2 == 0 ? '/even' : '/odd' %>">Link</a>)
+
+    include_examples 'theo to erb', 'evaluates shortened dynamic attribute',
+                     %(<a href%>Link</a>),
+                     %(<a href="<%= href %>">Link</a>)
+
+    include_examples 'theo to erb', 'evaluates shortened reserved dynamic attribute',
+                     %(<div class%>Content</div>),
+                     %(<div class="<%= binding.local_variable_get('class') %>">Content</div>)
+
+    include_examples 'theo to erb', 'ignores trim symbols',
+                     %(<%- variable -%>),
+                     %(<%- variable -%>)
   end
 
   context 'partial' do