fix posix.mq_receive compilation with cpp backend (#20710)

* fix posix.mq_receive compilation with cpp backend

* only enable runnableExample on posix

* linux, not posix

* simplify example

* add test

* mqueue.h does not exist on MacOS

* place test case in own block

* drop runnableExamples

lib/posix/posix.nim

@@ -249,26 +249,52 @@ proc setlocale*(a1: cint, a2: cstring): cstring {.
 proc strfmon*(a1: cstring, a2: int, a3: cstring): int {.varargs,
    importc, header: "<monetary.h>".}
 
-when not defined(nintendoswitch):
-  proc mq_close*(a1: Mqd): cint {.importc, header: "<mqueue.h>".}
-  proc mq_getattr*(a1: Mqd, a2: ptr MqAttr): cint {.
-    importc, header: "<mqueue.h>".}
-  proc mq_notify*(a1: Mqd, a2: ptr SigEvent): cint {.
-    importc, header: "<mqueue.h>".}
-  proc mq_open*(a1: cstring, a2: cint): Mqd {.
-    varargs, importc, header: "<mqueue.h>".}
-  proc mq_receive*(a1: Mqd, a2: cstring, a3: int, a4: var int): int {.
-    importc, header: "<mqueue.h>".}
-  proc mq_send*(a1: Mqd, a2: cstring, a3: int, a4: int): cint {.
-    importc, header: "<mqueue.h>".}
-  proc mq_setattr*(a1: Mqd, a2, a3: ptr MqAttr): cint {.
+when not (defined(nintendoswitch) or defined(macos) or defined(macosx)):
+  proc mq_notify*(mqdes: Mqd, event: ptr SigEvent): cint {.
     importc, header: "<mqueue.h>".}
 
-  proc mq_timedreceive*(a1: Mqd, a2: cstring, a3: int, a4: int,
-                        a5: ptr Timespec): int {.importc, header: "<mqueue.h>".}
-  proc mq_timedsend*(a1: Mqd, a2: cstring, a3: int, a4: int,
-                     a5: ptr Timespec): cint {.importc, header: "<mqueue.h>".}
-  proc mq_unlink*(a1: cstring): cint {.importc, header: "<mqueue.h>".}
+  proc mq_open*(name: cstring, flags: cint): Mqd {.
+    varargs, importc, header: "<mqueue.h>".}
+
+  proc mq_close*(mqdes: Mqd): cint {.importc, header: "<mqueue.h>".}
+
+  proc mq_receive*(
+    mqdes: Mqd,
+    buffer: cstring,
+    length: csize_t,
+    priority: var cuint
+  ): int {.importc, header: "<mqueue.h>".}
+
+  proc mq_timedreceive*(
+    mqdes: Mqd,
+    buffer: cstring,
+    length: csize_t,
+    priority: cuint,
+    timeout: ptr Timespec
+  ): int {.importc, header: "<mqueue.h>".}
+
+  proc mq_send*(
+    mqdes: Mqd,
+    buffer: cstring,
+    length: csize_t,
+    priority: cuint
+  ): cint {.importc, header: "<mqueue.h>".}
+
+  proc mq_timedsend*(
+    mqdes: Mqd,
+    buffer: cstring,
+    length: csize_t,
+    priority: cuint,
+    timeout: ptr Timespec
+  ): cint {.importc, header: "<mqueue.h>".}
+
+  proc mq_getattr*(mqdes: Mqd, attribute: ptr MqAttr): cint {.
+    importc, header: "<mqueue.h>".}
+
+  proc mq_setattr*(mqdes: Mqd, newAttribute, oldAttribute: ptr MqAttr): cint {.
+    importc, header: "<mqueue.h>".}
+
+  proc mq_unlink*(mqdes: cstring): cint {.importc, header: "<mqueue.h>".}
 
 
 proc getpwnam*(a1: cstring): ptr Passwd {.importc, header: "<pwd.h>".}

lib/posix/posix_macos_amd64.nim

@@ -108,15 +108,6 @@ type
     p_sign_posn*: char
     thousands_sep*: cstring
 
-  Mqd* {.importc: "mqd_t", header: "<mqueue.h>", final, pure.} = object
-  MqAttr* {.importc: "struct mq_attr",
-             header: "<mqueue.h>",
-             final, pure.} = object ## message queue attribute
-    mq_flags*: int   ## Message queue flags.
-    mq_maxmsg*: int  ## Maximum number of messages.
-    mq_msgsize*: int ## Maximum message size.
-    mq_curmsgs*: int ## Number of messages currently queued.
-
   Passwd* {.importc: "struct passwd", header: "<pwd.h>",
              final, pure.} = object ## struct passwd
     pw_name*: cstring   ## User's login name.

tests/stdlib/tposix.nim

@@ -7,7 +7,7 @@ outputsub: ""
 when not defined(windows):
 
   import posix
-  import std/syncio
+  import std/[assertions, syncio]
 
   var
     u: Utsname
@@ -18,3 +18,46 @@ when not defined(windows):
   writeLine(stdout, u.nodename)
   writeLine(stdout, u.release)
   writeLine(stdout, u.machine)
+
+  when not (defined(nintendoswitch) or defined(macos) or defined(macosx)):
+    block:
+      type Message = object
+        value: int
+
+      const MQ_PATH: cstring = "/top_level_file"
+      const MQ_PRIORITY: cuint = 170
+      const MQ_MESSAGE_SIZE: csize_t = csize_t(sizeof(Message))
+
+      let mqd_a: posix.MqAttr = MqAttr(mq_maxmsg: 10, mq_msgsize: clong(MQ_MESSAGE_SIZE))
+      let writable: posix.Mqd = posix.mq_open(
+        MQ_PATH,
+        posix.O_CREAT or posix.O_WRONLY or posix.O_NONBLOCK,
+        posix.S_IRWXU,
+        addr(mqd_a)
+      )
+      let readable: posix.Mqd = posix.mq_open(
+        MQ_PATH,
+        posix.O_RDONLY or posix.O_NONBLOCK,
+        posix.S_IRWXU,
+        addr(mqd_a)
+      )
+
+      let sent: Message = Message(value: 88)
+      block:
+        let success: int = writable.mq_send(
+          cast[cstring](sent.addr),
+          MQ_MESSAGE_SIZE,
+          MQ_PRIORITY
+        )
+        doAssert success == 0, $success
+
+      block:
+        var buffer: Message
+        var priority: cuint
+        let bytesRead: int = readable.mq_receive(
+          cast[cstring](buffer.addr),
+          MQ_MESSAGE_SIZE,
+          priority
+        )
+        doAssert buffer == sent
+        doAssert bytesRead == int(MQ_MESSAGE_SIZE)