From 5b81543769d4f59f6113bbad004465c6fb30e1f7 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Tue, 30 Aug 2022 16:34:14 -0500
Subject: [PATCH] Port to compilers that moan about K&R func decls
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* lib/autoconf/c.m4 (AC_LANG_CALL, AC_LANG_FUNC_LINK_TRY):
Use '(int)' rather than '()' in function prototypes, as the latter
provokes fatal errors in some compilers nowadays.
* lib/autoconf/functions.m4 (AC_FUNC_STRTOD):
* tests/semantics.at (AC_CHECK_DECLS):
Don’t use () in a function decl.
---
 doc/autoconf.texi         |  5 ++---
 lib/autoconf/c.m4         | 19 +++++--------------
 lib/autoconf/functions.m4 |  3 ---
 tests/semantics.at        |  2 +-
 4 files changed, 8 insertions(+), 21 deletions(-)

diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 67f31064..4f4ec741 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -5460,9 +5460,8 @@ the @samp{#undef malloc}):
 #include <config.h>
 #undef malloc
 
-#include <sys/types.h>
-
-void *malloc ();
+#include <stdlib.h>
+#undef malloc
 
 /* Allocate an N-byte block of memory from the heap.
    If N is zero, allocate a 1-byte block.  */
diff --git a/lib/autoconf/c.m4 b/lib/autoconf/c.m4
index abbb83fe..ca166557 100644
--- a/lib/autoconf/c.m4
+++ b/lib/autoconf/c.m4
@@ -126,14 +126,8 @@ m4_define([AC_LANG_CALL(C)],
 m4_if([$2], [main], ,
 [/* Override any GCC internal prototype to avoid an error.
    Use char because int might match the return type of a GCC
-   builtin and then its argument prototype would still apply.
-   The 'extern "C"' is for builds by C++ compilers;
-   although this is not generally supported in C code, supporting it here
-   has little cost and some practical benefit (sr 110532).  */
-#ifdef __cplusplus
-extern "C"
-#endif
-char $2 ();])], [return $2 ();])])
+   builtin and then its argument prototype would still apply.  */
+char $2 (int);])], [return $2 (0);])])
 
 
 # AC_LANG_FUNC_LINK_TRY(C)(FUNCTION)
@@ -157,7 +151,7 @@ m4_define([AC_LANG_FUNC_LINK_TRY(C)],
 #define $1 innocuous_$1
 
 /* System header to define __stub macros and hopefully few prototypes,
-   which can conflict with char $1 (); below.  */
+   which can conflict with char $1 (int); below.  */
 
 #include <limits.h>
 #undef $1
@@ -165,17 +159,14 @@ m4_define([AC_LANG_FUNC_LINK_TRY(C)],
 /* Override any GCC internal prototype to avoid an error.
    Use char because int might match the return type of a GCC
    builtin and then its argument prototype would still apply.  */
-#ifdef __cplusplus
-extern "C"
-#endif
-char $1 ();
+char $1 (int);
 /* The GNU C library defines this for functions which it implements
     to always fail with ENOSYS.  Some functions are actually named
     something starting with __ and the normal name is an alias.  */
 #if defined __stub_$1 || defined __stub___$1
 choke me
 #endif
-], [return $1 ();])])
+], [return $1 (0);])])
 
 
 # AC_LANG_BOOL_COMPILE_TRY(C)(PROLOGUE, EXPRESSION)
diff --git a/lib/autoconf/functions.m4 b/lib/autoconf/functions.m4
index 9f44a1ce..ee519a38 100644
--- a/lib/autoconf/functions.m4
+++ b/lib/autoconf/functions.m4
@@ -1613,9 +1613,6 @@ AC_DEFUN([AC_FUNC_STRTOD],
 AC_CACHE_CHECK(for working strtod, ac_cv_func_strtod,
 [AC_RUN_IFELSE([AC_LANG_SOURCE([[
 ]AC_INCLUDES_DEFAULT[
-#ifndef strtod
-double strtod ();
-#endif
 int
 main (void)
 {
diff --git a/tests/semantics.at b/tests/semantics.at
index d24c4551..276d9744 100644
--- a/tests/semantics.at
+++ b/tests/semantics.at
@@ -207,7 +207,7 @@ AT_CHECK_MACRO([AC_CHECK_DECLS],
 		 [[extern int yes;
 		   enum { myenum };
 		   extern struct mystruct_s { int x[20]; } mystruct;
-		   extern int myfunc();
+		   extern int myfunc (int);
 		   #define mymacro1(arg) arg
 		   #define mymacro2]])
   # Ensure we can detect missing declarations of functions whose
-- 
2.37.2