context-1

lib/liquid/tags.rb

@@ -1,24 +1,25 @@
 # frozen_string_literal: true
 
-require_relative "tags/table_row"
-require_relative "tags/echo"
-require_relative "tags/if"
-require_relative "tags/break"
-require_relative "tags/inline_comment"
-require_relative "tags/for"
-require_relative "tags/assign"
-require_relative "tags/ifchanged"
-require_relative "tags/case"
-require_relative "tags/include"
-require_relative "tags/continue"
-require_relative "tags/capture"
-require_relative "tags/decrement"
-require_relative "tags/unless"
-require_relative "tags/increment"
-require_relative "tags/comment"
-require_relative "tags/raw"
-require_relative "tags/render"
-require_relative "tags/cycle"
+require_relative 'tags/table_row'
+require_relative 'tags/echo'
+require_relative 'tags/if'
+require_relative 'tags/break'
+require_relative 'tags/inline_comment'
+require_relative 'tags/for'
+require_relative 'tags/assign'
+require_relative 'tags/ifchanged'
+require_relative 'tags/case'
+require_relative 'tags/include'
+require_relative 'tags/continue'
+require_relative 'tags/capture'
+require_relative 'tags/decrement'
+require_relative 'tags/unless'
+require_relative 'tags/increment'
+require_relative 'tags/comment'
+require_relative 'tags/raw'
+require_relative 'tags/render'
+require_relative 'tags/cycle'
+require_relative 'tags/let'
 
 module Liquid
   module Tags
@@ -42,6 +43,7 @@ module Liquid
       'if' => If,
       'echo' => Echo,
       'tablerow' => TableRow,
+      'let' => Let,
     }.freeze
   end
 end

lib/liquid/tags/let.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+module Liquid
+  class Let < Liquid::Block
+    MULTI_ASSIGNMENT = /\A\(\s*(?<vars>[^)]+)\s*\):\s*(?<source>[^\s]+)\z/
+    VAR_ASSIGNMENTS  = /(?<var>[\w-]+)\s*:\s*(?<expr>[^\s,]+)/
+
+    def initialize(tag_name, markup, options)
+      super(tag_name, markup, options)
+      @assignments = parse_markup(markup.strip)
+    end
+
+    def render(context)
+      subcontext = context.new_isolated_subcontext
+
+      @assignments.each do |var, expression|
+        subcontext[var] = lookup(context, expression)
+      end
+
+      super(subcontext)
+    end
+
+    private
+
+    def parse_markup(markup)
+      if (m = MULTI_ASSIGNMENT.match(markup))
+        variables = m[:vars].split(/\s*,\s*/)
+        source    = m[:source]
+        variables.map { |v| [v, "#{source}.#{v}"] }.to_h
+      else
+        markup.scan(VAR_ASSIGNMENTS).to_h
+      end
+    end
+
+    def lookup(context, expression)
+      variable_lookup = Liquid::VariableLookup.new(expression)
+      variable_lookup.evaluate(context)
+    end
+  end
+end