[commit: ghc] master: Clarify role of coercion in flattening function (45de833)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/45de833e3105245763b6c1652146b925ed42be46/ghc

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commit 45de833e3105245763b6c1652146b925ed42be46
Author: Richard Eisenberg <rae at cs.brynmawr.edu>
Date:   Thu Jun 28 00:08:58 2018 -0400

    Clarify role of coercion in flattening function
    
    Comments only: [ci skip]


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45de833e3105245763b6c1652146b925ed42be46
 compiler/typecheck/TcFlatten.hs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/compiler/typecheck/TcFlatten.hs b/compiler/typecheck/TcFlatten.hs
index f4176f5..f6a1adf 100644
--- a/compiler/typecheck/TcFlatten.hs
+++ b/compiler/typecheck/TcFlatten.hs
@@ -1432,7 +1432,8 @@ flatten_app_tys fun_ty arg_tys
        ; flatten_app_ty_args fun_xi fun_co arg_tys }
 
 -- Given a flattened function (with the coercion produced by flattening) and
--- a bunch of unflattened arguments, flatten the arguments and apply
+-- a bunch of unflattened arguments, flatten the arguments and apply.
+-- The coercion argument's role matches the role stored in the FlatM monad.
 --
 -- The bang patterns used here were observed to improve performance. If you
 -- wish to remove them, be sure to check for regeressions in allocations.