[Haml] Ensure that haml_buffer is reset even if an exception is raised.

Closes gh-53

doc-src/HAML_CHANGELOG.md

@@ -12,6 +12,9 @@
 * Fixed a bug in outer-whitespace nuking where whitespace-only Ruby strings
   blocked whitespace nuking beyond them.
 
+* Use `ensure` to protect the resetting of the Haml output buffer
+  against exceptions that are raised within the compiled Haml code.
+
 ## [2.2.10](http://github.com/nex3/haml/commit/2.2.10)
 
 * Fixed a bug where elements with dynamic attributes and no content

lib/haml/engine.rb

@@ -174,15 +174,13 @@ module Haml
         @haml_buffer = buffer
       end
 
-      str = eval(precompiled + ";" + precompiled_method_return_value,
+      eval(precompiled + ";" + precompiled_method_return_value,
         scope, @options[:filename], @options[:line])
-
+    ensure
       # Get rid of the current buffer
       scope_object.instance_eval do
         @haml_buffer = buffer.upper
       end
-
-      str
     end
     alias_method :to_html, :render
 

lib/haml/precompiler.rb

@@ -92,14 +92,17 @@ module Haml
     # Returns the precompiled string with the preamble and postamble
     def precompiled_with_ambles(local_names)
       preamble = <<END.gsub("\n", ";")
+begin
 extend Haml::Helpers
 _hamlout = @haml_buffer = Haml::Buffer.new(@haml_buffer, #{options_for_buffer.inspect})
 _erbout = _hamlout.buffer
 __in_erb_template = true
 END
       postamble = <<END.gsub("\n", ";")
-@haml_buffer = @haml_buffer.upper
 #{precompiled_method_return_value}
+ensure
+@haml_buffer = @haml_buffer.upper
+end
 END
       preamble + locals_code(local_names) + precompiled + postamble
     end

test/haml/engine_test.rb

@@ -962,6 +962,32 @@ END
     assert_equal("FOO\n", engine("= upcase").render_proc("foo".instance_eval{binding}).call)
   end
 
+  def test_haml_buffer_gets_reset_even_with_exception
+    scope = Object.new
+    render("- raise Haml::Error", :scope => scope)
+    assert(false, "Expected exception")
+  rescue Exception
+    assert_nil(scope.send(:haml_buffer))
+  end
+
+  def test_def_method_haml_buffer_gets_reset_even_with_exception
+    scope = Object.new
+    engine("- raise Haml::Error").def_method(scope, :render)
+    scope.render
+    assert(false, "Expected exception")
+  rescue Exception
+    assert_nil(scope.send(:haml_buffer))
+  end
+
+  def test_render_proc_haml_buffer_gets_reset_even_with_exception
+    scope = Object.new
+    proc = engine("- raise Haml::Error").render_proc(scope)
+    proc.call
+    assert(false, "Expected exception")
+  rescue Exception
+    assert_nil(scope.send(:haml_buffer))
+  end
+
   def test_ugly_true
     assert_equal("<div id='outer'>\n<div id='inner'>\n<p>hello world</p>\n</div>\n</div>\n",
                  render("#outer\n  #inner\n    %p hello world", :ugly => true))