From ed37542627dc767dd7468f439c222bb29489703c Mon Sep 17 00:00:00 2001
From: sheaf <sam.derbyshire@gmail.com>
Date: Sat, 30 Jul 2022 13:14:35 +0200
Subject: [PATCH] Avoid redundant pattern warning in Resource.hsc
With GHC MR !8478, GHC is able to spot a redundant pattern match
when RLIM_SAVED_CUR == RLIM_SAVED_MAX, which it wasn't able to
detect before. So we use considerAccessible to avoid a pattern match
check. This unfortunately means we must change the SafeHaskell status
of that module to TrustWorth, as considerAccessible is from GHC.Exts,
which isn't safe.
Alternatives:
- we can't perform the equality test RLIM_SAVED_CUR == RLIM_SAVED_MAX
using CPP macros, because one of the values might expand out to
have casts;
- turning off pattern match warnings impacts warnings across the whole
module, instead of the single affected function,
- adding a dummy equation such as "id True" to the first pattern match
would work, but seems more ad-hoc.
---
System/Posix/Resource.hsc | 22 +++++++++++++++++-----
1 file changed, 17 insertions(+), 5 deletions(-)
diff --git a/System/Posix/Resource.hsc b/System/Posix/Resource.hsc
index a909a34..8618ba7 100644
--- a/System/Posix/Resource.hsc
+++ b/System/Posix/Resource.hsc
@@ -1,5 +1,6 @@
{-# LANGUAGE CApiFFI #-}
-{-# LANGUAGE Safe #-}
+{-# LANGUAGE Trustworthy #-}
+
-----------------------------------------------------------------------------
-- |
-- Module : System.Posix.Resource
@@ -31,6 +32,9 @@ import Foreign.C
import System.IO.Error ( ioeSetLocation )
import GHC.IO.Exception ( unsupportedOperation )
#endif
+#if __GLASGOW_HASKELL__ >= 905
+import GHC.Exts ( considerAccessible )
+#endif
-- -----------------------------------------------------------------------------
-- Resource limits
@@ -115,12 +119,20 @@ unpackRLimit :: CRLim -> ResourceLimit
unpackRLimit (#const RLIM_INFINITY) = ResourceLimitInfinity
unpackRLimit other
#if defined(RLIM_SAVED_MAX)
- | ((#const RLIM_SAVED_MAX) :: CRLim) /= (#const RLIM_INFINITY) &&
- other == (#const RLIM_SAVED_MAX) = ResourceLimitUnknown
+ | ((#const RLIM_SAVED_MAX) :: CRLim) /= (#const RLIM_INFINITY)
+ , other == (#const RLIM_SAVED_MAX)
+ = ResourceLimitUnknown
#endif
#if defined(RLIM_SAVED_CUR)
- | ((#const RLIM_SAVED_CUR) :: CRLim) /= (#const RLIM_INFINITY) &&
- other == (#const RLIM_SAVED_CUR) = ResourceLimitUnknown
+ | ((#const RLIM_SAVED_CUR) :: CRLim) /= (#const RLIM_INFINITY)
+ , other == (#const RLIM_SAVED_CUR)
+#if __GLASGOW_HASKELL__ >= 905
+ , considerAccessible
+#endif
+ = ResourceLimitUnknown
+ -- (*) This pattern match is redundant if RLIM_SAVED_MAX and RLIM_SAVED_CUR
+ -- are both defined and are equal. This redundancy is only detected by GHC
+ -- starting from version 9.5, so we use 'considerAccessible'.
#endif
| otherwise = ResourceLimit (fromIntegral other)
--
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