All POSIX systems have langinfo.h and CODESET.

We don't need configure probes for HAVE_LANGINFO_H (it is implied by
!WIN32), and we don't need to consider systems that have it but don't
define CODESET (that was for OpenBSD in commit 81cca218, but it has now
had it for 19 years).

Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: https://postgr.es/m/CA%2BhUKGJqVe0%2BPv9dvC9dSums_PXxGo9SWcxYAMBguWJUGbWz-A%40mail.gmail.com

configure

@@ -13307,7 +13307,7 @@ $as_echo "#define HAVE_STDBOOL_H 1" >>confdefs.h
 fi
 
 
-for ac_header in atomic.h copyfile.h execinfo.h getopt.h ifaddrs.h langinfo.h mbarrier.h sys/epoll.h sys/event.h sys/personality.h sys/prctl.h sys/procctl.h sys/signalfd.h sys/ucred.h termios.h ucred.h
+for ac_header in atomic.h copyfile.h execinfo.h getopt.h ifaddrs.h mbarrier.h sys/epoll.h sys/event.h sys/personality.h sys/prctl.h sys/procctl.h sys/signalfd.h sys/ucred.h termios.h ucred.h
 do :
   as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
 ac_fn_c_check_header_mongrel "$LINENO" "$ac_header" "$as_ac_Header" "$ac_includes_default"

configure.ac

@@ -1447,7 +1447,6 @@ AC_CHECK_HEADERS(m4_normalize([
 	execinfo.h
 	getopt.h
 	ifaddrs.h
-	langinfo.h
 	mbarrier.h
 	sys/epoll.h
 	sys/event.h

meson.build

@@ -2394,7 +2394,6 @@ header_checks = [
   'execinfo.h',
   'getopt.h',
   'ifaddrs.h',
-  'langinfo.h',
   'mbarrier.h',
   'stdbool.h',
   'strings.h',

src/bin/pg_upgrade/pg_upgrade.c

@@ -40,10 +40,6 @@
 
 #include <time.h>
 
-#ifdef HAVE_LANGINFO_H
-#include <langinfo.h>
-#endif
-
 #include "catalog/pg_class_d.h"
 #include "common/file_perm.h"
 #include "common/logging.h"

src/include/pg_config.h.in

@@ -238,9 +238,6 @@
 /* Define to 1 if you have the `kqueue' function. */
 #undef HAVE_KQUEUE
 
-/* Define to 1 if you have the <langinfo.h> header file. */
-#undef HAVE_LANGINFO_H
-
 /* Define to 1 if you have the `ldap_initialize' function. */
 #undef HAVE_LDAP_INITIALIZE
 

src/port/chklocale.c

@@ -19,7 +19,7 @@
 #include "postgres_fe.h"
 #endif
 
-#ifdef HAVE_LANGINFO_H
+#ifndef WIN32
 #include <langinfo.h>
 #endif
 
@@ -287,8 +287,6 @@ pg_codepage_to_encoding(UINT cp)
 #endif
 #endif							/* WIN32 */
 
-#if (defined(HAVE_LANGINFO_H) && defined(CODESET)) || defined(WIN32)
-
 /*
  * Given a setting for LC_CTYPE, return the Postgres ID of the associated
  * encoding, if we can determine it.  Return -1 if we can't determine it.
@@ -415,19 +413,3 @@ pg_get_encoding_from_locale(const char *ctype, bool write_message)
 	free(sys);
 	return -1;
 }
-#else							/* (HAVE_LANGINFO_H && CODESET) || WIN32 */
-
-/*
- * stub if no multi-language platform support
- *
- * Note: we could return -1 here, but that would have the effect of
- * forcing users to specify an encoding to initdb on such platforms.
- * It seems better to silently default to SQL_ASCII.
- */
-int
-pg_get_encoding_from_locale(const char *ctype, bool write_message)
-{
-	return PG_SQL_ASCII;
-}
-
-#endif							/* (HAVE_LANGINFO_H && CODESET) || WIN32 */