redesign PBD::LocaleGuard to work correctly (i.e. not break translations)

libs/pbd/locale_guard.cc

@@ -29,54 +29,72 @@
 
 using namespace PBD;
 
-/* The initial C++ locale is "C" regardless of the user's preferred locale.
- * The C locale from setlocale() matches the user's preferred locale
+/* Neither C nor C++ pick up a user's preferred locale choice without the
+ * application actively taking steps to make this happen.
+ *
+ * For C: setlocale (LC_ALL, "");
+ * For C++ (assuming that the C version was called):
+ *      std::locale::global (std::locale (setlocale (LC_ALL, 0)));
+ *
+ * The application needs to make these calls, probably in main().
  *
  * Setting the C++ locale will change the C locale, but not the other way 'round.
  * and some plugin may change either behind our back.
  */
 
 LocaleGuard::LocaleGuard ()
-	: old_c (0)
+	: old_c_locale (0)
 {
-	char* actual = setlocale (LC_NUMERIC, NULL);
-	if (strcmp ("C", actual)) {
-		DEBUG_TRACE (DEBUG::Locale, string_compose ("LG: change locale from '%1' to 'C'\n", actual));
-		/* purpose of LocaleGuard is to make sure we're using "C" for
-		   the numeric locale during its lifetime, so make it so.
-		*/
-		old_c = strdup (actual);
-		/* this changes both C++ and C locale */
-		std::locale::global (std::locale (std::locale::classic(), "C", std::locale::numeric));
-	}
-	if (old_cpp != std::locale::classic ()) {
-		PBD::error << "LocaleGuard: initial C++ locale is not 'C'. Expect non-portable session files.\n";
-		DEBUG_TRACE (DEBUG::Locale, "LG: initial C++ locale is not 'C'. Expect non-portable session files.\n");
+	/* A LocaleGuard object ensures that the
+	 * LC_NUMERIC/std::locale::numeric aspect of the C and C++ locales are
+	 * set to "C" during its lifetime, so that printf/iostreams use a
+	 * portable format for numeric output (i.e. 1234.5 is always 1234.5 and
+	 * not sometimes 1234,5, as it would be in fr or de locales)
+	 */
+
+	char const * const current_c_locale = setlocale (LC_NUMERIC, 0);
+
+	if (strcmp ("C", current_c_locale) != 0) {
+
+		old_c_locale = strdup (current_c_locale);
+
+		/* set the C++ global/default locale to whatever we are using
+		 * now, but with "C" numeric handling.
+		 *
+		 * this also sets the C locale, so no call to setlocale() is required.
+		 */
+
+		std::locale::global (std::locale (old_cpp_locale, "C", std::locale::numeric));
+		pre_cpp_locale = std::locale();
+
+		DEBUG_TRACE (DEBUG::Locale, string_compose ("LG: change locale from '%1' => %2\n", old_cpp_locale.name(), pre_cpp_locale.name()));
 	}
 }
 
 LocaleGuard::~LocaleGuard ()
 {
-	char* actual = setlocale (LC_NUMERIC, NULL);
-	std::locale current;
+	char const * current_c_locale = setlocale (LC_NUMERIC, 0);
+	std::locale current_cpp_locale;
 
-	if (current != old_cpp) {
-		/* the C++ locale should always be "C", that's the default
-		 * at application start, and ardour never changes it to
-		 * anything but "C".
-		 *
-		 * if it's not: some plugin meddled with it.
-		 */
-		if (old_cpp != std::locale::classic ()) {
-			PBD::error << "LocaleGuard: someone (a plugin) changed the C++ locale, expect non-portable session files.\n";
-			DEBUG_TRACE (DEBUG::Locale, "LG: someone (a plugin) changed the C++ locale, expect non-portable session files.\n");
-		}
-		std::locale::global (old_cpp);
-		DEBUG_TRACE (DEBUG::Locale, string_compose ("LG: restore C++ locale: '%1'\n", old_cpp.name ()));
+	if (current_cpp_locale != pre_cpp_locale) {
+
+		PBD::error << string_compose ("LocaleGuard: someone (a plugin) changed the C++ locale from\n\t%1\nto\n\t%2\n, expect non-portable session files. Decimal OK ? %2",
+		                              old_cpp_locale.name(), current_cpp_locale.name(),
+		                              (std::use_facet<std::numpunct<char> >(std::locale()).decimal_point() == '.'))
+		           << endmsg;
+		DEBUG_TRACE (DEBUG::Locale, string_compose ("LG: someone (a plugin) changed the C++ locale (Decimal OK ? '%1'); expect non-portable session files.\n",
+		                                            (std::use_facet<std::numpunct<char> >(std::locale()).decimal_point() == '.')));
+
+		/* this resets C & C++ locales */
+		std::locale::global (old_cpp_locale);
+		DEBUG_TRACE (DEBUG::Locale, string_compose ("LG: restore C & C++ locale: '%1'\n", std::locale().name()));
+
+	} else if (old_c_locale && (strcmp (current_c_locale, old_c_locale) != 0)) {
+
+		/* reset only the C locale */
+		setlocale (LC_NUMERIC, old_c_locale);
+		DEBUG_TRACE (DEBUG::Locale, string_compose ("LG: restore C locale from %1 to\n'%2'\n(C++ is '%3')\n", current_c_locale, old_c_locale, std::locale().name()));
 	}
-	if (old_c && strcmp (old_c, actual)) {
-		setlocale (LC_NUMERIC, old_c);
-		DEBUG_TRACE (DEBUG::Locale, string_compose ("LG: restore C locale: '%1'\n", old_c));
-	}
-	free (old_c);
+
+	free (const_cast<char*> (old_c_locale));
 }

libs/pbd/pbd/locale_guard.h

@@ -26,15 +26,16 @@
 
 namespace PBD {
 
-	struct LIBPBD_API LocaleGuard {
-		public:
-			LocaleGuard ();
-			~LocaleGuard ();
+struct LIBPBD_API LocaleGuard {
+  public:
+	LocaleGuard ();
+	~LocaleGuard ();
 
-		private:
-			std::locale old_cpp;
-			char* old_c;
-	};
+  private:
+	std::locale old_cpp_locale;
+	std::locale pre_cpp_locale;
+	char const * old_c_locale;
+};
 }
 
 #endif /* __pbd_locale_guard__ */