Consider masked modifiers (~S etc.) when writing to bind file

Fixes #12973

(cherry picked from commit eb1ac06a9a)

src/KeyMap.cpp

@@ -568,11 +568,11 @@ void KeyMap::listBindings(BindingList & list,
 		// a LFUN_COMMAND_PREFIX
 		if (it->prefixes) {
 			KeySequence seq = prefix;
-			seq.addkey(it->code, it->mod.first);
+			seq.addkey(it->code, it->mod.first, it->mod.second);
 			it->prefixes->listBindings(list, seq, tag);
 		} else {
 			KeySequence seq = prefix;
-			seq.addkey(it->code, it->mod.first);
+			seq.addkey(it->code, it->mod.first, it->mod.second);
 			list.push_back(Binding(it->func, seq, tag));
 		}
 	}

src/KeySequence.cpp

@@ -147,16 +147,27 @@ docstring const KeySequence::print(outputFormat format, bool const untranslated)
 			break;
 		case BindFile:
 			KeyModifier mod = modifiers[i].first;
+			KeyModifier nmod = modifiers[i].second;
 			if (mod & ControlModifier)
 				buf += "C-";
+			else if (nmod & ControlModifier)
+				buf += "~C-";
 			if (mod & AltModifier)
 #if defined(USE_MACOSX_PACKAGING) || defined(USE_META_KEYBINDING)
 				buf += "A-";
+			else if (nmod & AltModifier)
+				buf += "~A-";
 			if (mod & MetaModifier)
 #endif
 				buf += "M-";
+#if defined(USE_MACOSX_PACKAGING) || defined(USE_META_KEYBINDING)
+			else if (nmod & MetaModifier)
+				buf += "~M-";
+#endif
 			if (mod & ShiftModifier)
 				buf += "S-";
+			else if (nmod & ShiftModifier)
+				buf += "~S-";
 
 			buf += from_utf8(sequence[i].getSymbolName());
 			break;

status.24x

@@ -74,6 +74,9 @@ What's new
 
 - Fix performance problems with references with (very) many authors.
 
+- Fix problem that key bindings that include optional modifier keys could not
+  be un- or re-bound (bug 12973)
+
 - Enable OK/Apply button in tabular dialog when "Additional Space" combo has
   been set to different value.