Explicitly set entire keymap if it was changed pre-scancode

src/defaultsettings.cpp

@@ -501,15 +501,15 @@ void set_default_settings()
 #endif
 }
 
+void set_keyboard_defaults(Settings *settings, bool force_keycode)
+{
 #define USEKEY(name, value) settings->setIfMissing(name, value)
 #if USE_SDL2
-#define USEKEY2(name, value, _) USEKEY(name, value)
+#define USEKEY2(name, value, legacy) USEKEY(name, (force_keycode) ? (legacy) : (value))
 #else
 #define USEKEY2(name, _, value) USEKEY(name, value)
 #endif
 
-void set_keyboard_defaults(Settings *settings)
-{
 	auto has_touch = detect_touch();
 
 	USEKEY2("save_keys_as_scancodes", "true", "false");
@@ -611,6 +611,6 @@ void set_keyboard_defaults(Settings *settings)
 	USEKEY("keymap_quicktune_dec", "");
 	USEKEY("keymap_quicktune_inc", "");
 #endif
-}
 #undef USEKEY
 #undef USEKEY2
+}

src/defaultsettings.h

@@ -15,5 +15,6 @@ void set_default_settings();
 /**
  * Use default preset for settings
  * @param settings pointer to settings
+ * @param force_keycode whether to unconditionally use keycode-based settings
  */
-void set_keyboard_defaults(Settings *settings);
+void set_keyboard_defaults(Settings *settings, bool force_keycode = false);

src/migratesettings.h

@@ -1,7 +1,7 @@
 // Minetest
 // SPDX-License-Identifier: LGPL-2.1-or-later
 
-#include "settings.h"
+#include "defaultsettings.h"
 #include "server.h"
 
 void migrate_settings()
@@ -28,4 +28,17 @@ void migrate_settings()
 		}
 		g_settings->remove("disable_anticheat");
 	}
+
+	// Use keycodes for keybindings for missing keys
+	// if the keymap was changed in an earlier version
+#if USE_SDL2
+	if (!g_settings->existsLocal("use_scancodes_for_keybindings"))
+		for (const auto &name: g_settings->getNames())
+			if (auto value = g_settings->get(name);
+					str_starts_with(name, "keymap_") && value.size() > 1 && value.front() != '<') {
+				g_settings->setBool("use_scancodes_for_keybindings", false);
+				set_keyboard_defaults(g_settings, true);
+				break;
+			}
+#endif
 }