Properly introduce CTimer to System.Posix.Types

Summary:
In ffc2327070dbb664bdb407a804121eacb2a7c734, an attempt was made at
adding a Haskell wrapper around the C `timer_t` type. Unfortunately, GHC's
autoconf macros weren't sophisticated enough at the time to properly detect
that `timer_t` is represented by a `void *` (i.e., a pointer) on most OSes.

This is a second attempt at `CTimer`, this time using `AC_COMPILE_IFELSE` to
detect if a type is a pointer type by compiling the following program:

```
type val;
*val;
```

This also only derives a small subset of class instances for `CTimer` that are
known to be compatible with `Ptr` using a new `OPAQUE_TYPE_WITH_CTYPE` macro.

Test Plan: ./validate

Reviewers: erikd, hvr, austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2952

GHC Trac Issues: #12795, #12998

5 files changed, 50 insertions, 26 deletions

diff --git a/libraries/base/System/Posix/Types.hs b/libraries/base/System/Posix/Types.hs
index da4fc608d9..a02a5b94e4 100644
--- a/libraries/base/System/Posix/Types.hs
+++ b/libraries/base/System/Posix/Types.hs
@@ -92,13 +92,9 @@ module System.Posix.Types (
 #if defined(HTYPE_KEY_T)
   CKey(..),
 #endif
--- We can't support CTimer (timer_t) yet, as FPTOOLS_CHECK_HTYPE doesn't have
--- the ability to discern pointer types (like void*, which timer_t usually is)
--- from non-pointer types. See GHC Trac #12998.
---
--- #if defined(HTYPE_TIMER_T)
---   CTimer(..),
--- #endif
+#if defined(HTYPE_TIMER_T)
+  CTimer(..),
+#endif
 
   Fd(..),
 
@@ -213,6 +209,10 @@ INTEGRAL_TYPE_WITH_CTYPE(CId,id_t,HTYPE_ID_T)
 -- | @since 4.10.0.0
 INTEGRAL_TYPE_WITH_CTYPE(CKey,key_t,HTYPE_KEY_T)
 #endif
+#if defined(HTYPE_TIMER_T)
+-- | @since 4.10.0.0
+OPAQUE_TYPE_WITH_CTYPE(CTimer,timer_t,HTYPE_TIMER_T)
+#endif
 
 -- Make an Fd type rather than using CInt everywhere
 INTEGRAL_TYPE(Fd,CInt)
diff --git a/libraries/base/aclocal.m4 b/libraries/base/aclocal.m4
index 50d8168ec0..17b8bca9ce 100644
--- a/libraries/base/aclocal.m4
+++ b/libraries/base/aclocal.m4
@@ -131,26 +131,43 @@ AC_DEFUN([FPTOOLS_CHECK_HTYPE_ELSE],[
 
         if test "$HTYPE_IS_INTEGRAL" -eq 0
         then
-            FP_COMPUTE_INT([HTYPE_IS_FLOAT],[sizeof($1) == sizeof(float)],
-                           [FPTOOLS_HTYPE_INCLUDES],
-                           [AC_CV_NAME_supported=no])
-            FP_COMPUTE_INT([HTYPE_IS_DOUBLE],[sizeof($1) == sizeof(double)],
-                           [FPTOOLS_HTYPE_INCLUDES],
-                           [AC_CV_NAME_supported=no])
-            FP_COMPUTE_INT([HTYPE_IS_LDOUBLE],[sizeof($1) == sizeof(long double)],
-                           [FPTOOLS_HTYPE_INCLUDES],
-                           [AC_CV_NAME_supported=no])
-            if test "$HTYPE_IS_FLOAT" -eq 1
-            then
-                AC_CV_NAME=Float
-            elif test "$HTYPE_IS_DOUBLE" -eq 1
-            then
-                AC_CV_NAME=Double
-            elif test "$HTYPE_IS_LDOUBLE" -eq 1
+            dnl If the C type isn't an integer, we check if it's a pointer type
+            dnl by trying to dereference one of its values. If that fails to
+            dnl compile, it's not a pointer, so we check to see if it's a
+            dnl floating-point type.
+            AC_COMPILE_IFELSE(
+                [AC_LANG_PROGRAM(
+                    [FPTOOLS_HTYPE_INCLUDES],
+                    [$1 val; *val;]
+                )],
+                [HTYPE_IS_POINTER=yes],
+                [HTYPE_IS_POINTER=no])
+
+            if test "$HTYPE_IS_POINTER" = yes
             then
-                AC_CV_NAME=LDouble
+                AC_CV_NAME="Ptr ()"
             else
-                AC_CV_NAME_supported=no
+                FP_COMPUTE_INT([HTYPE_IS_FLOAT],[sizeof($1) == sizeof(float)],
+                               [FPTOOLS_HTYPE_INCLUDES],
+                               [AC_CV_NAME_supported=no])
+                FP_COMPUTE_INT([HTYPE_IS_DOUBLE],[sizeof($1) == sizeof(double)],
+                               [FPTOOLS_HTYPE_INCLUDES],
+                               [AC_CV_NAME_supported=no])
+                FP_COMPUTE_INT([HTYPE_IS_LDOUBLE],[sizeof($1) == sizeof(long double)],
+                               [FPTOOLS_HTYPE_INCLUDES],
+                               [AC_CV_NAME_supported=no])
+                if test "$HTYPE_IS_FLOAT" -eq 1
+                then
+                    AC_CV_NAME=Float
+                elif test "$HTYPE_IS_DOUBLE" -eq 1
+                then
+                    AC_CV_NAME=Double
+                elif test "$HTYPE_IS_LDOUBLE" -eq 1
+                then
+                    AC_CV_NAME=LDouble
+                else
+                    AC_CV_NAME_supported=no
+                fi
             fi
         else
             FP_COMPUTE_INT([HTYPE_IS_SIGNED],[(($1)(-1)) < (($1)0)],
diff --git a/libraries/base/changelog.md b/libraries/base/changelog.md
index b73e01ecc0..d687e07cb7 100644
--- a/libraries/base/changelog.md
+++ b/libraries/base/changelog.md
@@ -31,7 +31,7 @@
   * Added `Eq1`, `Ord1`, `Read1` and `Show1` instances for `NonEmpty`.
 
   * Add wrappers for `blksize_t`, `blkcnt_t`, `clockid_t`, `fsblkcnt_t`,
-    `fsfilcnt_t`, `id_t`, and `key_t` to System.Posix.Types (#12795)
+    `fsfilcnt_t`, `id_t`, `key_t`, and `timer_t` to System.Posix.Types (#12795)
 
   * Raw buffer operations in `GHC.IO.FD` are now strict in the buffer, offset, and length operations (#9696)
 
diff --git a/libraries/base/configure.ac b/libraries/base/configure.ac
index c99c284c93..e6c8a9b276 100644
--- a/libraries/base/configure.ac
+++ b/libraries/base/configure.ac
@@ -155,6 +155,7 @@ FPTOOLS_CHECK_HTYPE(fsblkcnt_t)
 FPTOOLS_CHECK_HTYPE(fsfilcnt_t)
 FPTOOLS_CHECK_HTYPE(id_t)
 FPTOOLS_CHECK_HTYPE(key_t)
+FPTOOLS_CHECK_HTYPE(timer_t)
 
 FPTOOLS_CHECK_HTYPE(intptr_t)
 FPTOOLS_CHECK_HTYPE(uintptr_t)
diff --git a/libraries/base/include/CTypes.h b/libraries/base/include/CTypes.h
index 9fa1e4a1c1..e9d19a8401 100644
--- a/libraries/base/include/CTypes.h
+++ b/libraries/base/include/CTypes.h
@@ -19,6 +19,7 @@
 #define ARITHMETIC_CLASSES  Eq,Ord,Num,Enum,Storable,Real
 #define INTEGRAL_CLASSES Bounded,Integral,Bits,FiniteBits
 #define FLOATING_CLASSES Fractional,Floating,RealFrac,RealFloat
+#define OPAQUE_CLASSES Eq,Ord,Storable
 
 #define ARITHMETIC_TYPE(T,B) \
 newtype T = T B deriving (ARITHMETIC_CLASSES) \
@@ -42,4 +43,9 @@ newtype {-# CTYPE "THE_CTYPE" #-} T = T B \
     deriving (ARITHMETIC_CLASSES, FLOATING_CLASSES) \
     deriving newtype (Read, Show);
 
+#define OPAQUE_TYPE_WITH_CTYPE(T,THE_CTYPE,B) \
+newtype {-# CTYPE "THE_CTYPE" #-} T = T (B) \
+    deriving (OPAQUE_CLASSES) \
+    deriving newtype Show;
+
 #endif