Replace @haml_stack with a linked list of buffers.

This is done via the new Buffer#upper property.

lib/haml/buffer.rb

@@ -18,6 +18,11 @@ module Haml
     # The options hash passed in from Haml::Engine.
     attr_accessor :options
 
+    # The Buffer for the enclosing Haml document.
+    # This is set for partials and similar sorts of nested templates.
+    # It's nil at the top level (see #toplevel?).
+    attr_accessor :upper
+
     # True if the format is XHTML
     def xhtml?
       not html?
@@ -38,6 +43,12 @@ module Haml
       @options[:format] == :html5
     end
 
+    # True if this buffer is a top-level template,
+    # as opposed to a nested partial.
+    def toplevel?
+      upper.nil?
+    end
+
     # Gets the current tabulation of the document.
     def tabulation
       @real_tabs + @tabulation
@@ -50,7 +61,8 @@ module Haml
     end
 
     # Creates a new buffer.
-    def initialize(options = {})
+    def initialize(upper = nil, options = {})
+      @upper = upper
       @options = {
         :attr_wrapper => "'",
         :ugly => false,

lib/haml/engine.rb

@@ -147,7 +147,7 @@ END
     # they won't work.
     def render(scope = Object.new, locals = {}, &block)
       locals = (@options[:locals] || {}).merge(locals)
-      buffer = Haml::Buffer.new(options_for_buffer)
+      buffer = Haml::Buffer.new(scope.instance_variable_get('@haml_buffer'), options_for_buffer)
 
       if scope.is_a?(Binding) || scope.is_a?(Proc)
         scope_object = eval("self", scope)
@@ -161,8 +161,7 @@ END
 
       scope_object.instance_eval do
         extend Haml::Helpers
-        @haml_stack ||= Array.new
-        @haml_stack.push(buffer)
+        @haml_buffer = buffer
         @haml_is_haml = true
       end
 
@@ -170,7 +169,7 @@ END
 
       # Get rid of the current buffer
       scope_object.instance_eval do
-        @haml_stack.pop
+        @haml_buffer = buffer.upper
         @haml_is_haml = false
       end
 

lib/haml/helpers.rb

@@ -38,7 +38,7 @@ module Haml
     #
     def init_haml_helpers
       @haml_is_haml = true
-      @haml_stack = [Haml::Buffer.new(Haml::Engine.new('').send(:options_for_buffer))]
+      @haml_buffer = Haml::Buffer.new(@haml_buffer, Haml::Engine.new('').send(:options_for_buffer))
       nil
     end
 
@@ -345,7 +345,7 @@ END
 
     # Gets a reference to the current Haml::Buffer object.
     def haml_buffer
-      @haml_stack[-1]
+      @haml_buffer
     end
 
     # Gives a proc the same local "_hamlout" and "_erbout" variables

lib/haml/precompiler.rb

@@ -97,15 +97,14 @@ module Haml
     def precompiled_with_ambles(local_names)
       preamble = <<END.gsub("\n", ";")
 extend Haml::Helpers
-@haml_stack ||= Array.new
-@haml_stack.push(Haml::Buffer.new(#{options_for_buffer.inspect}))
+_hamlout = @haml_buffer = Haml::Buffer.new(@haml_buffer, #{options_for_buffer.inspect})
 @haml_is_haml = true
-_hamlout = @haml_stack[-1]
 _erbout = _hamlout.buffer
 END
       postamble = <<END.gsub("\n", ";")
 @haml_is_haml = false
-@haml_stack.pop.buffer
+@haml_buffer = @haml_buffer.upper
+_erbout
 END
       preamble + locals_code(local_names) + @precompiled + postamble
     end