Fix some infinite mixin loops.

doc-src/SASS_CHANGELOG.md

@@ -7,6 +7,8 @@
 
 * Compatibility with the `mathn` library (thanks to [Thomas Walpole](https://github.com/twalpole)).
 
+* Fix some infinite loops with mixins that were previously uncaught.
+
 ## 3.1.11
 
 * Allow control directives (such as `@if`) to be nested beneath properties.

lib/sass/environment.rb

@@ -59,7 +59,7 @@ def push_frame(frame_info)
       else
         stack.push(top_of_stack = frame_info)
       end
-      mixins_in_use << top_of_stack[:mixin] if top_of_stack[:mixin] && !top_of_stack[:prepared]
+      mixins_in_use << top_of_stack[:mixin] if top_of_stack[:mixin]
     end
 
     # Like \{#push\_frame}, but next time a stack frame is pushed,
@@ -72,9 +72,8 @@ def prepare_frame(frame_info)
 
     # Pop a stack frame from the mixin/include stack.
     def pop_frame
-      stack.pop if stack.last && stack.last[:prepared]
-      popped = stack.pop
-      mixins_in_use.delete(popped[:mixin]) if popped && popped[:mixin]
+      pop_and_unuse if stack.last && stack.last[:prepared]
+      pop_and_unuse
     end
 
     # A list of stack frames in the mixin/include stack.
@@ -106,6 +105,12 @@ def stack_trace
 
     private
 
+    def pop_and_unuse
+      popped = stack.pop
+      mixins_in_use.delete(popped[:mixin]) if popped && popped[:mixin]
+      popped
+    end
+
     def parent_options
       @parent_options ||= @parent && @parent.options
     end

lib/sass/tree/visitors/perform.rb

@@ -293,9 +293,7 @@ def run_interp(text)
   def handle_include_loop!(node)
     msg = "An @include loop has been found:"
     mixins = @environment.stack.map {|s| s[:mixin]}.compact
-    if mixins.size == 2 && mixins[0] == mixins[1]
-      raise Sass::SyntaxError.new("#{msg} #{node.name} includes itself")
-    end
+    raise Sass::SyntaxError.new("#{msg} #{node.name} includes itself") if mixins.size == 1
 
     mixins << node.name
     msg << "\n" << Sass::Util.enum_cons(mixins, 2).map do |m1, m2|

test/sass/engine_test.rb

@@ -2041,6 +2041,24 @@ def test_media_with_parent_references
 
   # Regression tests
 
+  def test_tricky_mixin_loop_exception
+    render <<SASS
+@mixin foo($a)
+  @if $a
+    @include foo(false)
+    @include foo(true)
+  @else
+    a: b
+
+a
+  @include foo(true)
+SASS
+    assert(false, "Exception not raised")
+  rescue Sass::SyntaxError => err
+    assert_equal("An @include loop has been found: foo includes itself", err.message)
+    assert_hash_has(err.sass_backtrace[0], :mixin => "foo", :line => 3)
+  end
+
   def test_interpolated_comment_in_mixin
     assert_equal <<CSS, render(<<SASS)
 /* color: red */