Fix finalization after failure (#161)

* Fix finalization after failure

It appears to have only worked coincidentally before. When the
interpreter enters into a finalization block, it puts a `Finalized` node
onto the attempt stack with the current `step`. However if there was
a failure, then step would be null. It "worked" before because there was
stale state, and `fail` could be preserved through finalization. This
bug was exposed by using `catchError` within the finalization block,
which resets the failure state to null. Thus when it resumes after
finalization, both `step` and `fail` are null, which is an invalid
state. The solution is to preserve `fail` in addition to `step` in
a `Finalized` node.

* Cleanup potentially stale state

src/Effect/Aff.js

@@ -261,12 +261,11 @@ var Aff = function () {
     // the provided callback in `makeAff` more than once, but it may also be an
     // async effect resuming after the fiber was already cancelled.
     function run(localRunTick) {
-      var tmp, result, attempt, canceler;
+      var tmp, result, attempt;
       while (true) {
         tmp       = null;
         result    = null;
         attempt   = null;
-        canceler  = null;
 
         switch (status) {
         case STEP_BIND:
@@ -460,7 +459,7 @@ var Aff = function () {
             // because it should not be cancelled.
             case RELEASE:
               bracketCount++;
-              attempts = new Aff(CONS, new Aff(FINALIZED, step), attempts, interrupt);
+              attempts = new Aff(CONS, new Aff(FINALIZED, step, fail), attempts, interrupt);
               status   = CONTINUE;
               // It has only been killed if the interrupt status has changed
               // since we enqueued the item.
@@ -471,11 +470,12 @@ var Aff = function () {
               } else {
                 step = attempt._1.completed(util.fromRight(step))(attempt._2);
               }
+              fail = null;
               break;
 
             case FINALIZER:
               bracketCount++;
-              attempts = new Aff(CONS, new Aff(FINALIZED, step), attempts, interrupt);
+              attempts = new Aff(CONS, new Aff(FINALIZED, step, fail), attempts, interrupt);
               status   = CONTINUE;
               step     = attempt._1;
               break;
@@ -484,6 +484,7 @@ var Aff = function () {
               bracketCount--;
               status = RETURN;
               step   = attempt._1;
+              fail   = attempt._2;
               break;
             }
           }

test/Test/Main.purs

@@ -651,6 +651,15 @@ test_regression_par_apply_async_canceler = assert "regression/par-apply-async-ca
       val <- readRef ref
       pure (val == "throwdone" && message err == "Nope.")
 
+test_regression_bracket_catch_cleanup ∷ Aff Unit
+test_regression_bracket_catch_cleanup = assert "regression/bracket-catch-cleanup" do
+  res :: Either Error Unit ←
+    try $ bracket
+      (pure unit)
+      (\_ → catchError (pure unit) (const (pure unit)))
+      (\_ → throwError (error "Nope."))
+  pure $ lmap message res == Left "Nope."
+
 main ∷ Effect Unit
 main = do
   test_pure
@@ -697,3 +706,4 @@ main = do
     test_parallel_stack
     test_regression_return_fork
     test_regression_par_apply_async_canceler
+    test_regression_bracket_catch_cleanup