Perl_langinfo: Teach about YESSTR and NOSTR

These are items that nl_langinfo() used to be required to return, but
are considered obsolete.  Nonetheless, this drop-in replacement for that
function should know about them for backward compatibility.

ext/XS-APItest/t/locale.t

@@ -83,12 +83,14 @@ my %correct_C_responses = (
                             MON_8 => 'August',
                             MON_9 => 'September',
                             NOEXPR => undef,
+                            NOSTR => undef,
                             PM_STR => 'PM',
                             RADIXCHAR => '.',
                             THOUSEP => '',
                             T_FMT => undef,
                             T_FMT_AMPM => undef,
                             YESEXPR => undef,
+                            YESSTR => undef,
                         );
 
 my $hdr = "../../perl_langinfo.h";

locale.c

@@ -1275,11 +1275,15 @@ Unimplemented, so returns C<"">.
 
 =item C<YESEXPR>
 
+=item C<YESSTR>
+
 =item C<NOEXPR>
 
-Only the values for English are returned.  Earlier POSIX standards also
-specified C<YESSTR> and C<NOSTR>, but these have been removed from POSIX 2008,
-and aren't supported by C<Perl_langinfo>.
+=item C<NOSTR>
+
+Only the values for English are returned.  C<YESSTR> and C<NOSTR> have been
+removed from POSIX 2008, and are retained for backwards compatibility.  Your
+platform's C<nl_langinfo> may not support them.
 
 =item C<D_FMT>
 
@@ -1409,8 +1413,6 @@ S_my_nl_langinfo(const int item, bool toggle)
 
     LOCALE_UNLOCK;
 
-    return PL_langinfo_buf;
-
 #  else /* Use nl_langinfo_l(), avoiding both a mutex and changing the locale */
 
     bool do_free = FALSE;
@@ -1434,9 +1436,19 @@ S_my_nl_langinfo(const int item, bool toggle)
         freelocale(cur);
     }
 
+#  endif
+
+    if (strEQ(PL_langinfo_buf, "")) {
+        if (item == PERL_YESSTR) {
+            return "yes";
+        }
+        if (item == PERL_NOSTR) {
+            return "no";
+        }
+    }
+
     return PL_langinfo_buf;
 
-#    endif
 #else   /* Below, emulate nl_langinfo as best we can */
 #  ifdef HAS_LOCALECONV
 
@@ -1472,7 +1484,9 @@ S_my_nl_langinfo(const int item, bool toggle)
 
         /* We use only an English set, since we don't know any more */
         case PERL_YESEXPR:   return "^[+1yY]";
+        case PERL_YESSTR:    return "yes";
         case PERL_NOEXPR:    return "^[-0nN]";
+        case PERL_NOSTR:     return "no";
 
 #  ifdef HAS_LOCALECONV
 

perl_langinfo.h

@@ -283,15 +283,25 @@
 #else
 #  define PERL_YESEXPR -53
 #endif
+#ifdef YESSTR
+#  define PERL_YESSTR YESSTR
+#else
+#  define PERL_YESSTR -54
+#endif
 #ifdef NOEXPR
 #  define PERL_NOEXPR NOEXPR
 #else
-#  define PERL_NOEXPR -54
+#  define PERL_NOEXPR -55
+#endif
+#ifdef NOSTR
+#  define PERL_NOSTR NOSTR
+#else
+#  define PERL_NOSTR -56
 #endif
 #ifdef CRNCYSTR
 #  define PERL_CRNCYSTR CRNCYSTR
 #else
-#  define PERL_CRNCYSTR -55
+#  define PERL_CRNCYSTR -57
 #endif
 
 #endif