Uniques should not appear in error messages

I noticed this failure in the CircleCI output:

--- ./patsyn/should_fail/T14507.run/T14507.stderr.normalised	2018-01-22 18:57:32.381575253 +0000
+++ ./patsyn/should_fail/T14507.run/T14507.comp.stderr.normalised	2018-01-22 18:57:32.381575253 +0000
@@ -2,7 +2,7 @@
 T14507.hs:18:9:
      Iceland Jack!  Iceland Jack! Stop torturing me!
       Pattern-bound variable x :: TypeRep a
-        has a type that mentions pattern-bound coercion: co_a2CF
+        has a type that mentions pattern-bound coercion: co_a2D4
       Hint: use -fprint-explicit-coercions to see the coercions
       Probable fix: add a pattern signature
      In the declaration for pattern synonym ‘SO’

Trac metadata

Trac field	Value
Version	8.4.1-alpha1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Test Suite
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