Nice error tracing for @content chains.

lib/sass/tree/visitors/perform.rb

@@ -218,7 +218,13 @@ def visit_mixin(node)
 
   def visit_content(node)
     raise Sass::SyntaxError.new("No @content passed.") unless content = @environment.content
-    with_environment(@environment.caller) {content.map {|c| visit(c.dup)}}
+    trace_node = Sass::Tree::TraceNode.from_node('@content', node)
+    with_environment(@environment.caller) {trace_node.children = content.map {|c| visit(c.dup)}}
+    trace_node
+  rescue Sass::SyntaxError => e
+    e.modify_backtrace(:mixin => '@content', :line => node.line)
+    e.add_backtrace(:line => node.line)
+    raise e
   end
 
   # Runs any SassScript that may be embedded in a property.

test/sass/engine_test.rb

@@ -2612,6 +2612,42 @@ def test_content_not_seen_through_mixin
     assert_equal(7, e.sass_line)
   end
 
+  def test_content_backtrace_for_perform
+    render(<<SASS)
+=foo
+  @content
+
+a
+  +foo
+    b: 1em + 2px
+SASS
+    assert(false, "Expected exception")
+  rescue Sass::SyntaxError => e
+    assert_equal([
+        {:mixin => '@content', :line => 6, :filename => 'test_content_backtrace_for_perform_inline.sass'},
+        {:mixin => 'foo', :line => 2, :filename => 'test_content_backtrace_for_perform_inline.sass'},
+        {:line => 5, :filename => 'test_content_backtrace_for_perform_inline.sass'},
+      ], e.sass_backtrace)
+  end
+
+  def test_content_backtrace_for_cssize
+    render(<<SASS)
+=foo
+  @content
+
+a
+  +foo
+    @extend foo bar baz
+SASS
+    assert(false, "Expected exception")
+  rescue Sass::SyntaxError => e
+    assert_equal([
+        {:mixin => '@content', :line => 6, :filename => 'test_content_backtrace_for_cssize_inline.sass'},
+        {:mixin => 'foo', :line => 2, :filename => 'test_content_backtrace_for_cssize_inline.sass'},
+        {:line => 5, :filename => 'test_content_backtrace_for_cssize_inline.sass'},
+      ], e.sass_backtrace)
+  end
+
   private
 
   def assert_hash_has(hash, expected)