Create a deterministic version of tyVarsOfType

I've run into situations where I need deterministic `tyVarsOfType` and
this implementation achieves that and also brings an algorithmic
improvement.  Union of two `VarSet`s takes linear time the size of the
sets and in the worst case we can have `n` unions of sets of sizes
`(n-1, 1), (n-2, 1)...` making it quadratic.

One reason why we need deterministic `tyVarsOfType` is in `abstractVars`
in `SetLevels`. When we abstract type variables when floating we want
them to be abstracted in deterministic order.

Test Plan: harbormaster

Reviewers: simonpj, goldfire, austin, hvr, simonmar, bgamari

Reviewed By: simonmar

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1468

GHC Trac Issues: #4012

1 files changed, 24 insertions, 24 deletions

diff --git a/testsuite/tests/polykinds/T9222.stderr b/testsuite/tests/polykinds/T9222.stderr
index 1d1a1df779..a5b35ee2b1 100644
--- a/testsuite/tests/polykinds/T9222.stderr
+++ b/testsuite/tests/polykinds/T9222.stderr
@@ -1,24 +1,24 @@
-

-T9222.hs:13:3: error:

-    Couldn't match type ‘b0’ with ‘b’

-      ‘b0’ is untouchable

-        inside the constraints: a ~ '(b0, c0)

-        bound by the type of the constructor ‘Want’:

-                   (a ~ '(b0, c0)) => Proxy b0

-        at T9222.hs:13:3

-      ‘b’ is a rigid type variable bound by

-          the type of the constructor ‘Want’:

-            ((a ~ '(b, c)) => Proxy b) -> Want a

-          at T9222.hs:13:3

-    Expected type: '(b, c)

-      Actual type: a

-    In the ambiguity check for the type of the constructor ‘Want’:

-      Want :: forall (k :: BOX)

-                     (k1 :: BOX)

-                     (a :: (,) k k1)

-                     (b :: k)

-                     (c :: k1).

-              ((a ~ '(b, c)) => Proxy b) -> Want a

-    To defer the ambiguity check to use sites, enable AllowAmbiguousTypes

-    In the definition of data constructor ‘Want’

-    In the data type declaration for ‘Want’

+
+T9222.hs:13:3: error:
+    Couldn't match type ‘b0’ with ‘b’
+      ‘b0’ is untouchable
+        inside the constraints: a ~ '(b0, c0)
+        bound by the type of the constructor ‘Want’:
+                   (a ~ '(b0, c0)) => Proxy b0
+        at T9222.hs:13:3
+    ‘b’ is a rigid type variable bound by
+        the type of the constructor ‘Want’:
+          ((a ~ '(b, c)) => Proxy b) -> Want a
+        at T9222.hs:13:3
+    Expected type: '(b, c)
+      Actual type: a
+    In the ambiguity check for the type of the constructor ‘Want’:
+      Want :: forall (k :: BOX)
+                     (k1 :: BOX)
+                     (a :: (,) k k1)
+                     (b :: k)
+                     (c :: k1).
+              ((a ~ '(b, c)) => Proxy b) -> Want a
+    To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
+    In the definition of data constructor ‘Want’
+    In the data type declaration for ‘Want’