Ungrammatical error message involving a pattern binding

Take a look at this error message from GHC's Typeable1 test case:

Typeable1.hs:22:5: error: [-Winaccessible-code (in -Wdefault), -Werror=inaccessible-code]
    • Couldn't match type ‘ComposeK’ with ‘a3 b3’
      Inaccessible code in
        a pattern with pattern synonym:
          App :: forall k2 (t :: k2).
                 () =>
                 forall k1 (a :: k1 -> k2) (b :: k1).
                 (t ~ a b) =>
                 TypeRep a -> TypeRep b -> TypeRep t,
        in a pattern binding in
             'do' block

In particular, note the "in a pattern binding in 'do' block" part. I think that should be "in **a** 'do' block".

I believe fixing this is a simple matter of applying this patch:

diff --git a/compiler/hsSyn/HsExpr.hs b/compiler/hsSyn/HsExpr.hs
index 96d86c8..a5c65fb 100644
--- a/compiler/hsSyn/HsExpr.hs
+++ b/compiler/hsSyn/HsExpr.hs
@@ -2804,7 +2804,7 @@ pprMatchContextNoun PatBindGuards   = text "pattern binding guards"
 pprMatchContextNoun LambdaExpr      = text "lambda abstraction"
 pprMatchContextNoun ProcExpr        = text "arrow abstraction"
 pprMatchContextNoun (StmtCtxt ctxt) = text "pattern binding in"
-                                      $$ pprStmtContext ctxt
+                                      $$ pprAStmtContext ctxt
 pprMatchContextNoun PatSyn          = text "pattern synonym declaration"
 
 -----------------

Patch incoming.

Trac metadata

Trac field	Value
Version	8.4.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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