Parser.y: clarify treatment of @{-# UNPACK #-}wip/no-at-unpack

Before this patch, we had this parser production:

	ftype : ...
	      | ftype PREFIX_AT tyarg  { ... }

And 'tyarg' is defined as follows:

	tyarg : atype              { ... }
	      | unpackedness atype { ... }

So one might get the (false) impression that that parser production is
intended to parse things like:

	F @{-# UNPACK #-} X

However, the lexer wouldn't produce PREFIX_AT followed by 'unpackedness',
as the '@' operator followed by '{-' is not considered prefix.

Thus there's no point using 'tyarg' after PREFIX_AT,
and a simple 'atype' will suffice:

	ftype : ...
	      | ftype PREFIX_AT atype  { ... }

This change has no user-facing consequences. It just makes the grammar a
bit more clear.

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/GHC/Parser.y b/compiler/GHC/Parser.y
index 50f63796ee..b71027699c 100644
--- a/compiler/GHC/Parser.y
+++ b/compiler/GHC/Parser.y
@@ -1981,7 +1981,7 @@ ftype :: { forall b. DisambTD b => PV (Located b) }
         | tyop                          { failOpFewArgs $1 }
         | ftype tyarg                   { $1 >>= \ $1 ->
                                           mkHsAppTyPV $1 $2 }
-        | ftype PREFIX_AT tyarg         { $1 >>= \ $1 ->
+        | ftype PREFIX_AT atype         { $1 >>= \ $1 ->
                                           mkHsAppKindTyPV $1 (getLoc $2) $3 }
 
 tyarg :: { LHsType GhcPs }