Fix 'printf %T' ignoring the current locale in LC_TIME (#263)

src/lib/libast/tm/tmlocale.c:
- Load the locale set by LC_TIME or LC_ALL if it hasn't been loaded
  before or if it was loaded previously but isn't the current locale.

src/cmd/ksh93/tests/locale.sh:
- Add a regression test using the nl_NL.UTF-8 and ja_JP.UTF-8 locales.

Fixes: https://github.com/ksh93/ksh/issues/261

NEWS

@@ -8,6 +8,9 @@ Any uppercase BUG_* names are modernish shell bug IDs.
 - Path-bound builtins will now be used by restricted shells if /opt/ast/bin
   is in the $PATH upon invoking the shell or before setting it to restricted.
 
+- Fixed a bug that caused "printf '%T\n' now" to ignore $LC_ALL and $LC_TIME
+  if the current locale was previously set, unset then set again.
+
 2021-04-07:
 
 - The $LC_TIME variable is now recognized by ksh and if set to an invalid

src/cmd/ksh93/tests/locale.sh

@@ -85,10 +85,29 @@ do	[[ $locale == *[Jj][Ii][Ss] ]] || continue
 done
 unset LC_ALL
 
+# Test the effect of setting a locale, followed by setting a different locale
+# then setting the previous locale. The output from 'printf %T' should use
+# the current locale.
+# https://github.com/ksh93/ksh/issues/261
+((SHOPT_MULTIBYTE)) && for locale in "${locales[@]}"
+do	[[ $locale == *nl_NL*[Uu][Tt][Ff]* ]] && nl_NL=$locale
+	[[ $locale == *ja_JP*[Uu][Tt][Ff]* ]] && ja_JP=$locale
+done
+if [[ -n $nl_NL ]] && [[ -n $ja_JP ]]; then
+	LC_ALL=$nl_NL
+	exp=$(printf '%(%A)T' now)
+	LC_ALL=$ja_JP
+	printf '%T' now > /dev/null
+	LC_ALL=$nl_NL
+	got=$(printf '%(%A)T' now)
+	[[ $exp == $got ]] || err_exit "'printf %T' ignores changes to LC_ALL when locale is set, unset then set (expected $exp, got $got)"
+fi
+unset LC_ALL
+
 # this locale is supported by ast on all platforms
 # EU for { decimal_point="," thousands_sep="." }
 
-if((SHOPT_MULTIBYTE)); then
+if ((SHOPT_MULTIBYTE)); then
 locale=C_EU.UTF-8
 else
 locale=C_EU

src/lib/libast/tm/tmlocale.c

@@ -637,8 +637,14 @@ tmlocale(void)
 		else if (tm_info.deformat != tm_info.format[TM_DEFAULT])
 			state.format = tm_info.deformat;
 	}
+
+	/* load the locale set in LC_TIME */
 	li = LCINFO(AST_LC_TIME);
-	if (!li->data)
+	if (!li->data || state.locale != li)
+	{
 		load(li);
+		state.locale = li;
+	}
+
 	return tm_info.format;
 }