Do not complain about SPECIALISE for INLINE

Fixes Trac #10721.
See Note [SPECIALISE on INLINE functions]

1 files changed, 17 insertions, 8 deletions

diff --git a/compiler/deSugar/DsBinds.hs b/compiler/deSugar/DsBinds.hs
index b6edf7c35f..55c82dd0dc 100644
--- a/compiler/deSugar/DsBinds.hs
+++ b/compiler/deSugar/DsBinds.hs
@@ -67,9 +67,7 @@ import Bag
 import BasicTypes hiding ( TopLevel )
 import DynFlags
 import FastString
-import ErrUtils( MsgDoc )
 import Util
-import Control.Monad( when )
 import MonadUtils
 import Control.Monad(liftM)
 import Fingerprint(Fingerprint(..), fingerprintString)
@@ -460,8 +458,10 @@ dsSpec mb_poly_rhs (L loc (SpecPrag poly_id spec_co spec_inl))
 
        ; spec_rhs <- dsHsWrapper spec_co poly_rhs
 
-       ; when (isInlinePragma id_inl && wopt Opt_WarnPointlessPragmas dflags)
-              (warnDs (specOnInline poly_name))
+-- Commented out: see Note [SPECIALISE on INLINE functions]
+--       ; when (isInlinePragma id_inl)
+--              (warnDs $ ptext (sLit "SPECIALISE pragma on INLINE function probably won't fire:")
+--                        <+> quotes (ppr poly_name))
 
        ; return (Just (unitOL (spec_id, spec_rhs), rule))
             -- NB: do *not* use makeCorePair on (spec_id,spec_rhs), because
@@ -503,11 +503,20 @@ dsSpec mb_poly_rhs (L loc (SpecPrag poly_id spec_co spec_inl))
              | otherwise   = spec_prag_act                   -- Specified by user
 
 
-specOnInline :: Name -> MsgDoc
-specOnInline f = ptext (sLit "SPECIALISE pragma on INLINE function probably won't fire:")
-                 <+> quotes (ppr f)
 
-{-
+{- Note [SPECIALISE on INLINE functions]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We used to warn that using SPECIALISE for a function marked INLINE
+would be a no-op; but it isn't!  Especially with worker/wrapper split
+we might have
+   {-# INLINE f #-}
+   f :: Ord a => Int -> a -> ...
+   f d x y = case x of I# x' -> $wf d x' y
+
+We might want to specialise 'f' so that we in turn specialise '$wf'.
+We can't even /name/ '$wf' in the source code, so we can't specialise
+it even if we wanted to.  Trac #10721 is a case in point.
+
 Note [Activation pragmas for SPECIALISE]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 From a user SPECIALISE pragma for f, we generate