[Sass] Keep track of the runtime stack so it can be inspected without unwinding.

lib/sass/environment.rb

@@ -23,7 +23,8 @@ module Sass
       @vars = {}
       @mixins = {}
       @parent = parent
-
+      @stack = []
+      @ignore_parent_stack = false
       set_var("important", Script::String.new("!important")) unless @parent
     end
 
@@ -35,6 +36,49 @@ module Sass
       @options || (parent && parent.options) || {}
     end
 
+    # Push lexical frame information onto the runtime stack.
+    # @param frame_info [{Symbol => Object}]
+    # Frame information has the following keys:
+    #
+    # `:filename`
+    # : The name of the file in which the lexical scope changed.
+    #
+    # `:mixin`
+    # : The name of the mixin in which the lexical scope changed,
+    #   or `nil` if it wasn't within in a mixin.
+    #
+    # `:line`
+    # : The line of the file on which the lexical scope changed. Never nil.
+    #
+    # `:import`
+    # : Set to `true` when the lexical scope is changing due to an import.
+    def push(frame_info)
+      @stack.push frame_info
+    end
+
+    # Pop runtime frame information from the stack.
+    def pop
+      @stack.pop
+    end
+
+    # A list of the runtime stack frame information
+    # The last element in the list was pushed onto the stack most recently.
+    def stack
+      prev = (!@ignore_parent_stack && parent && parent.stack) || []
+      prev + @stack
+    end
+
+    # Temporarily assume the runtime stack that is passed in.
+    # @param stk A stack value from another environment.
+    def with_stack(stk)
+      @stack, old_stack = stk, @stack
+      @ignore_parent_stack = true
+      yield self
+    ensure
+      @ignore_parent_stack = false
+      @stack = old_stack
+    end
+
     class << self
       private
 

lib/sass/tree/import_node.rb

@@ -62,6 +62,7 @@ module Sass
       # @param environment [Sass::Environment] The lexical environment containing
       #   variable and mixin values
       def perform!(environment)
+        environment.push(:filename => @filename, :line => @line, :import => true)
         root = Sass::Files.tree_for(full_filename, @options)
         @template = root.template
         self.children = root.children
@@ -70,6 +71,8 @@ module Sass
         e.modify_backtrace(:filename => full_filename)
         e.add_backtrace(:filename => @filename, :line => @line)
         raise e
+      ensure
+        environment.pop
       end
 
       private

lib/sass/tree/mixin_node.rb

@@ -50,6 +50,8 @@ module Sass::Tree
     # @raise [Sass::SyntaxError] if an incorrect number of arguments was passed
     # @see Sass::Tree
     def perform!(environment)
+      original_env = environment
+      original_env.push(:filename => filename, :mixin => @name, :line => line)
       raise Sass::SyntaxError.new("Undefined mixin '#{@name}'.") unless mixin = environment.mixin(@name)
 
       raise Sass::SyntaxError.new(<<END.gsub("\n", "")) if mixin.args.size < @args.size
@@ -57,27 +59,30 @@ Mixin #{@name} takes #{mixin.args.size} argument#{'s' if mixin.args.size != 1}
  but #{@args.size} #{@args.size == 1 ? 'was' : 'were'} passed.
 END
 
-      environment = mixin.args.zip(@args).
-        inject(Sass::Environment.new(mixin.environment)) do |env, ((var, default), value)|
-        env.set_local_var(var.name,
-          if value
-            value.perform(environment)
-          elsif default
-            val = default.perform(env)
-            if default.context == :equals && val.is_a?(Sass::Script::String)
-              val = Sass::Script::String.new(val.value)
-            end
-            val
-          end)
-        raise Sass::SyntaxError.new("Mixin #{@name} is missing parameter #{var.inspect}.") unless env.var(var.name)
-        env
+      mixin.environment.with_stack(original_env.stack) do |mixin_env|
+        environment = mixin.args.zip(@args).
+          inject(Sass::Environment.new(mixin_env)) do |env, ((var, default), value)|
+          env.set_local_var(var.name,
+            if value
+              value.perform(environment)
+            elsif default
+              val = default.perform(env)
+              if default.context == :equals && val.is_a?(Sass::Script::String)
+                val = Sass::Script::String.new(val.value)
+              end
+              val
+            end)
+          raise Sass::SyntaxError.new("Mixin #{@name} is missing parameter #{var.inspect}.") unless env.var(var.name)
+          env
+        end
+        self.children = mixin.tree.map {|c| c.perform(environment)}.flatten
       end
-
-      self.children = mixin.tree.map {|c| c.perform(environment)}.flatten
     rescue Sass::SyntaxError => e
       e.modify_backtrace(:mixin => @name, :line => @line)
       e.add_backtrace(:line => @line)
       raise e
+    ensure
+      original_env.pop
     end
   end
 end