Compile error with OpenBSD and clang 19

[rhelmot]

Describe the bug
jq will not compile for OpenBSD under clang 19 due to -Werror=implicit-function-declaration being automatic.

Sample errors:

   > src/builtin.c:247:31: error: call to undeclared function 'lgamma_r'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]                                                               
   >   247 |   jv ret = JV_ARRAY(jv_number(lgamma_r(jv_number_value(input), &sign)));                                                                                                                                                     
   >       |                               ^                                                                                                                                                                                              
   > src/builtin.c:1341:10: error: call to undeclared function 'timegm'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]                                                                
   >  1341 |   return timegm(tm);                                                                                                                                                                                                         
   >       |          ^ 

To Reproduce
./configure && make

Expected behavior
A clear and concise description of what you expected to happen.

Environment (please complete the following information):
OpenBSD 7.5, clang 19

Additional context
Fixed with CFLAGS=-D_BSD_SOURCE=1. Autoconf detects these symbols in -lm but they are not visible in headers by default.

[itchyny]

This patch works?

diff --git a/src/builtin.c b/src/builtin.c
index c0aba96..146c4d0 100644
--- a/src/builtin.c
+++ b/src/builtin.c
@@ -5,6 +5,10 @@
 # define _XPG6
 # define __EXTENSIONS__
 #endif
+#ifdef __GLIBC__
+# define _BSD_SOURCE
+# define _DEFAULT_SOURCE
+#endif
 #include <sys/time.h>
 #include <stdlib.h>
 #include <stddef.h>

[emanuele6]

I thought this line from configure.ac was supposed to automatically define _BSD_SOURCE on OpenBSD:

jq/configure.ac

Line 8 in fa6a2ff

AC_USE_SYSTEM_EXTENSIONS

---

Hmm, no apparently it only sets _OPENBSD_SOURCE ("Enable OpenBSD compatibility extensions on NetBSD. Oddly enough, this does nothing on OpenBSD."), and only on NetBSD; it never sets _BSD_SOURCE:
https://www.gnu.org/software/autoconf/manual/autoconf-2.72/html_node/C-and-Posix-Variants.html

It also depends on the version of autoconf; in 2.65, it doesn't even set _OPENBSD_SOURCE:
https://www.gnu.org/software/autoconf/manual/autoconf-2.65/html_node/Posix-Variants.html

You can only rely on this macro to set _GNU_SOURCE/_POSIX_SOURCE, but not _BSD_SOURCE.

[itchyny]

Add to CFLAGS?

diff --git a/Makefile.am b/Makefile.am
index c7504e4..cb09065 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -20,7 +20,7 @@ LIBJQ_SRC = src/builtin.c src/bytecode.c src/compile.c src/execute.c    \
 ### C build options
 
 AM_CFLAGS = -Wextra -Wall -Wno-unused-parameter -Wno-unused-function \
-            -Woverlength-strings
+            -Woverlength-strings -D_BSD_SOURCE -D_DEFAULT_SOURCE
 
 if WIN32
 AM_CFLAGS += -municode