From 8214c68a385b94af779b653205102b5a8be18ec4 Mon Sep 17 00:00:00 2001
From: Joshua Root <jmr@macports.org>
Date: Mon, 14 Dec 2020 07:56:34 +1100
Subject: [PATCH] bpo-42598: Fix implicit function declarations in configure
 (GH-23690)

This is invalid in C99 and later and is an error with some compilers
(e.g. clang in Xcode 12), and can thus cause configure checks to
produce incorrect results.
(cherry picked from commit 674fa0a740151e0416c9383f127b16014e805990)

Co-authored-by: Joshua Root <jmr@macports.org>
---
 .../Build/2020-12-13-14-43-10.bpo-42598.7ipr5H.rst  |  2 ++
 configure                                           | 13 +++++++------
 configure.ac                                        | 13 +++++++------
 3 files changed, 16 insertions(+), 12 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Build/2020-12-13-14-43-10.bpo-42598.7ipr5H.rst

diff --git a/Misc/NEWS.d/next/Build/2020-12-13-14-43-10.bpo-42598.7ipr5H.rst b/Misc/NEWS.d/next/Build/2020-12-13-14-43-10.bpo-42598.7ipr5H.rst
new file mode 100644
index 00000000000000..7dafc105c45ea9
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2020-12-13-14-43-10.bpo-42598.7ipr5H.rst
@@ -0,0 +1,2 @@
+Fix implicit function declarations in configure which could have resulted in
+incorrect configuration checks.  Patch contributed by Joshua Root.
diff --git a/configure b/configure
index dfb6e7ef3f0f79..15ea8cdfdc0f06 100755
--- a/configure
+++ b/configure
@@ -10928,10 +10928,10 @@ else
       main() {
         pthread_attr_t attr;
         pthread_t id;
-        if (pthread_attr_init(&attr)) exit(-1);
-        if (pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM)) exit(-1);
-        if (pthread_create(&id, &attr, foo, NULL)) exit(-1);
-        exit(0);
+        if (pthread_attr_init(&attr)) return (-1);
+        if (pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM)) return (-1);
+        if (pthread_create(&id, &attr, foo, NULL)) return (-1);
+        return (0);
       }
 _ACEOF
 if ac_fn_c_try_run "$LINENO"; then :
@@ -14916,7 +14916,7 @@ else
   int main()
   {
 	/* Success: exit code 0 */
-        exit((((wchar_t) -1) < ((wchar_t) 0)) ? 0 : 1);
+        return ((((wchar_t) -1) < ((wchar_t) 0)) ? 0 : 1);
   }
 
 _ACEOF
@@ -15261,7 +15261,7 @@ else
 
 int main()
 {
-	exit(((-1)>>3 == -1) ? 0 : 1);
+	return (((-1)>>3 == -1) ? 0 : 1);
 }
 
 _ACEOF
@@ -15731,6 +15731,7 @@ else
 /* end confdefs.h.  */
 
 #include <poll.h>
+#include <unistd.h>
 
 int main()
 {
diff --git a/configure.ac b/configure.ac
index 6c8fd5a3892778..c93ba0ee7dc0e0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3210,10 +3210,10 @@ if test "$posix_threads" = "yes"; then
       main() {
         pthread_attr_t attr;
         pthread_t id;
-        if (pthread_attr_init(&attr)) exit(-1);
-        if (pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM)) exit(-1);
-        if (pthread_create(&id, &attr, foo, NULL)) exit(-1);
-        exit(0);
+        if (pthread_attr_init(&attr)) return (-1);
+        if (pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM)) return (-1);
+        if (pthread_create(&id, &attr, foo, NULL)) return (-1);
+        return (0);
       }]])],
       [ac_cv_pthread_system_supported=yes],
       [ac_cv_pthread_system_supported=no],
@@ -4616,7 +4616,7 @@ then
   int main()
   {
 	/* Success: exit code 0 */
-        exit((((wchar_t) -1) < ((wchar_t) 0)) ? 0 : 1);
+        return ((((wchar_t) -1) < ((wchar_t) 0)) ? 0 : 1);
   }
   ]])],
   [ac_cv_wchar_t_signed=yes],
@@ -4709,7 +4709,7 @@ AC_CACHE_VAL(ac_cv_rshift_extends_sign, [
 AC_RUN_IFELSE([AC_LANG_SOURCE([[
 int main()
 {
-	exit(((-1)>>3 == -1) ? 0 : 1);
+	return (((-1)>>3 == -1) ? 0 : 1);
 }
 ]])],
 [ac_cv_rshift_extends_sign=yes],
@@ -4856,6 +4856,7 @@ AC_MSG_CHECKING(for broken poll())
 AC_CACHE_VAL(ac_cv_broken_poll,
 AC_RUN_IFELSE([AC_LANG_SOURCE([[
 #include <poll.h>
+#include <unistd.h>
 
 int main()
 {