Add for_loop? to Include tag for AST-based keyword detection

[aswamy]

Summary

Stores @is_for_loop during parsing in the Include tag, matching the existing pattern in the Render tag. This allows consumers (like the liquid-rewriter) to determine the with/for keyword from the parsed AST instead of re-parsing raw markup with regex.

Changes:

• Added FOR = 'for' constant
• Added for_loop? public method
• strict2_parse: captures the with/for token from p.id? and stores @is_for_loop
• lax_parse: updated SYNTAX regex to capture the keyword in its own group (group 3), stores @is_for_loop
• Regex capture groups shifted: variable name is now group 4, alias name is now group 6

No runtime behavior change — Include#render_to_output_buffer still uses variable.is_a?(Array) for iteration, not @is_for_loop.

Depends on: Shopify/liquid-rewriter-private#214

Tophat

bundle install
bundle exec irb -r liquid

# for keyword detected
t = Liquid::Template.parse("{% include 'product' for products %}")
t.root.nodelist.first.for_loop?  # => true

# with keyword detected
t = Liquid::Template.parse("{% include 'product' with product %}")
t.root.nodelist.first.for_loop?  # => false

# no keyword
t = Liquid::Template.parse("{% include 'header' %}")
t.root.nodelist.first.for_loop?  # => false

🤖 Generated with Claude Code

[charlespwd]

Looks good but let's remove that comment. IDK why claude loves these so much. I struggle with em too.