Add MR2537-use-one-shot-kqueue-on-macos.patch (#604)

This adds the one-shot-kqueue-on-macos MR from gitlab.

Author: angerman

overlays/bootstrap.nix

@@ -101,7 +101,7 @@ in {
                 ++ fromUntil "8.6.4" "8.8"   ./patches/ghc/global-offset-table.patch
                 ++ fromUntil "8.6.4" "8.8"   ./patches/ghc/global-offset-table-2.patch
                 ++ always                    ./patches/ghc/respect-ar-path.patch
-
+                ++ until             "8.12"  ./patches/ghc/MR2537-use-one-shot-kqueue-on-macos.patch 
                 ++ final.lib.optional (version == "8.6.3") ./patches/ghc/T16057--ghci-doa-on-windows.patch
                 ++ final.lib.optional (version == "8.6.3") ./patches/ghc/ghc-8.6.3-reinstallable-lib-ghc.patch
                 ++ final.lib.optional (version == "8.6.4") ./patches/ghc/ghc-8.6.4-reinstallable-lib-ghc.patch

overlays/patches/ghc/MR2537-use-one-shot-kqueue-on-macos.patch

@@ -0,0 +1,52 @@
+From 41117d71bb58e001f6a2b6a11c9314d5b70b9182 Mon Sep 17 00:00:00 2001
+From: Ben Gamari <[email protected]>
+Date: Thu, 23 Jan 2020 14:11:20 -0500
+Subject: [PATCH] base: Use one-shot kqueue on macOS
+
+The underlying reason requiring that one-shot usage be disabled (#13903)
+has been fixed.
+
+Closes #15768.
+---
+ libraries/base/GHC/Event/Manager.hs | 17 ++---------------
+ 1 file changed, 2 insertions(+), 15 deletions(-)
+
+diff --git a/libraries/base/GHC/Event/Manager.hs b/libraries/base/GHC/Event/Manager.hs
+index eda3e61490..51306795fe 100644
+--- a/libraries/base/GHC/Event/Manager.hs
++++ b/libraries/base/GHC/Event/Manager.hs
+@@ -150,9 +150,7 @@ callbackTableVar mgr fd = emFds mgr ! hashFd fd
+ 
+ haveOneShot :: Bool
+ {-# INLINE haveOneShot #-}
+-#if defined(darwin_HOST_OS) || defined(ios_HOST_OS)
+-haveOneShot = False
+-#elif defined(HAVE_EPOLL) || defined(HAVE_KQUEUE)
++#if defined(HAVE_EPOLL) || defined(HAVE_KQUEUE)
+ haveOneShot = True
+ #else
+ haveOneShot = False
+@@ -365,20 +363,9 @@ registerFd mgr cb fd evs lt = do
+   return r
+ {-# INLINE registerFd #-}
+ 
+-{-
+-    Building GHC with parallel IO manager on Mac freezes when
+-    compiling the dph libraries in the phase 2. As workaround, we
+-    don't use oneshot and we wake up an IO manager on Mac every time
+-    when we register an event.
+-
+-    For more information, please read:
+-        http://ghc.haskell.org/trac/ghc/ticket/7651
+--}
+ -- | Wake up the event manager.
+ wakeManager :: EventManager -> IO ()
+-#if defined(darwin_HOST_OS) || defined(ios_HOST_OS)
+-wakeManager mgr = sendWakeup (emControl mgr)
+-#elif defined(HAVE_EPOLL) || defined(HAVE_KQUEUE)
++#if defined(HAVE_EPOLL) || defined(HAVE_KQUEUE)
+ wakeManager _ = return ()
+ #else
+ wakeManager mgr = sendWakeup (emControl mgr)
+-- 
+2.25.0