I18N: Do not mark empty strings for a translation

An empty string has a special meaning in gettext and marking such
string produces invalid catalogs with a duplicate message ID entry.

We cannot use simply Error("") necause Error() expects
BgettextMessage argument. Therefore I added EMPTY_MESSAGE macro which
expands to the same as M_(""), but is not caught by xgettext.

I think it's cleaner solution than overriding xgettext behaviour for
that line of code. For aesthetic reasons I also disabled clang-format
at two places.

Fixes: #1158

include/libdnf5/utils/bgettext/bgettext-mark-domain.h

@@ -26,6 +26,10 @@ along with libdnf.  If not, see <https://www.gnu.org/licenses/>.
 
 #include "bgettext-mark-common.h"
 
+// clang-format off
+// Use EMPTY_MESSAGE instead of M_(""). Otherwise, xgettext breaks catalogs.
+#define EMPTY_MESSAGE \
+    { .bgettextMsg = "\004" GETTEXT_DOMAIN "\00" "" }
 #define M_(msgId) \
     { .bgettextMsg = "\004" GETTEXT_DOMAIN "\00" msgId }
 #define MP_(msgId, msgIdPlural) \
@@ -34,5 +38,6 @@ along with libdnf.  If not, see <https://www.gnu.org/licenses/>.
     { .bgettextMsg = "\006" GETTEXT_DOMAIN "\00" context "\004" msgId }
 #define MCP_(context, msgId, msgIdPlural) \
     { .bgettextMsg = "\007" GETTEXT_DOMAIN "\00" context "\004" msgId "\00" msgIdPlural }
+//clang-format on
 
 #endif /* _BGETTEXT_MARK_DOMAIN_H_ */

include/libdnf5/utils/bgettext/bgettext-mark.h

@@ -22,6 +22,10 @@ along with libdnf.  If not, see <https://www.gnu.org/licenses/>.
 
 #include "bgettext-mark-common.h"
 
+// clang-format off
+// Use EMPTY_MESSAGE instead of M_(""). Otherwise, xgettext breaks catalogs.
+#define EMPTY_MESSAGE \
+    { .bgettextMsg = "\000" "" }
 #define M_(msgId) \
     { .bgettextMsg = "\000" msgId }
 #define MP_(msgId, msgIdPlural) \
@@ -30,5 +34,6 @@ along with libdnf.  If not, see <https://www.gnu.org/licenses/>.
     { .bgettextMsg = "\002" context "\004" msgId }
 #define MCP_(context, msgId, msgIdPlural) \
     { .bgettextMsg = "\003" context "\004" msgId "\00" msgIdPlural }
+// clang-format on
 
 #endif /* _BGETTEXT_MARK_H_ */

libdnf5-cli/exception.cpp

@@ -46,6 +46,6 @@ const char * GoalResolveError::what() const noexcept {
     return message.c_str();
 }
 
-SilentCommandExitError::SilentCommandExitError(int exit_code) : Error(M_("")), exit_code(exit_code) {}
+SilentCommandExitError::SilentCommandExitError(int exit_code) : Error(EMPTY_MESSAGE), exit_code(exit_code) {}
 
 }  // namespace libdnf5::cli