Fix #capture when run with a block that returns a string.

Closes hamlgh-387.

doc-src/HAML_CHANGELOG.md

@@ -3,6 +3,11 @@
 * Table of contents
 {:toc}
 
+## 3.1.2 (Unreleased)
+
+* If the ActionView `#capture` helper is used in a Haml template but without any Haml being run in the block,
+  return the value of the block rather than the captured buffer.
+
 ## 3.1.1
 
 * Update the vendored Sass to version 3.1.0.

lib/haml/helpers/action_view_mods.rb

@@ -51,7 +51,10 @@ def capture_with_haml(*args, &block)
           # We've got to do the same thing for compatibility.
 
           if is_haml? && block_is_haml?(block)
-            capture_haml(*args, &block)
+            value = nil
+            buffer = capture_haml(*args) { value = yield(*args) }
+            return buffer unless buffer.empty?
+            return value if value.is_a?(String)
           else
             capture_without_haml(*args, &block)
           end
@@ -85,7 +88,16 @@ def concat_with_haml(string, binding = nil)
       module CaptureHelper
         def capture_with_haml(*args, &block)
           if Haml::Helpers.block_is_haml?(block)
-            str = capture_haml(*args, &block)
+            value = nil
+            buffer = capture_haml(*args) { value = yield(*args) }
+            str =
+              if !buffer.empty?
+                buffer
+              elsif value.is_a?(String)
+                value
+              else
+                ''
+              end
             return ActionView::NonConcattingString.new(str) if defined?(ActionView::NonConcattingString)
             return str
           else

test/haml/helper_test.rb

@@ -357,6 +357,10 @@ def trc(collection, &block)
     assert_equal("1\n\n2\n\n3\n\n", render("- trc([1, 2, 3]) do |i|\n  = i.inspect"))
   end
 
+  def test_capture_with_string_block
+    assert_equal("foo\n", render("= capture { 'foo' }", :action_view))
+  end
+
   def test_find_and_preserve_with_block
     assert_equal("<pre>Foo&#x000A;Bar</pre>\nFoo\nBar\n",
                  render("= find_and_preserve do\n  %pre\n    Foo\n    Bar\n  Foo\n  Bar"))