qml wizard: stricter validation for new wallet name

user on bitcointalk [0] tried to create wallet with name "w/o 2FA".
Before this, one would only get an error after the last page of the wizard.
With this, the "Next" button does not even get enabled if the name does not look ok.
(and as in comment, maybe we should be even stricter re what is allowed)

[0]: https://bitcointalk.org/index.php?topic=5483514.msg63584789#msg63584789

electrum/gui/qml/components/wizard/WCWalletName.qml

@@ -5,7 +5,7 @@ import QtQuick.Controls
 import org.electrum 1.0
 
 WizardComponent {
-    valid: wallet_name.text.length > 0 && !Daemon.availableWallets.wallet_name_exists(wallet_name.text)
+    valid: wiz.isValidNewWalletName(wallet_name.text)
 
     function apply() {
         wizard_data['wallet_name'] = wallet_name.text

electrum/gui/qml/qewizard.py

@@ -6,6 +6,8 @@ from PyQt6.QtCore import pyqtProperty, pyqtSignal, pyqtSlot, QObject
 from electrum.logging import get_logger
 from electrum import mnemonic
 from electrum.wizard import NewWalletWizard, ServerConnectWizard
+from electrum.storage import WalletStorage, StorageReadWriteError
+from electrum.util import WalletFileException
 
 if TYPE_CHECKING:
     from electrum.gui.qml.qedaemon import QEDaemon
@@ -116,6 +118,30 @@ class QENewWalletWizard(NewWalletWizard, QEAbstractWizard):
             'message': validation_message
         }
 
+    def _wallet_path_from_wallet_name(self, wallet_name: str) -> str:
+        return os.path.join(self._qedaemon.daemon.config.get_datadir_wallet_path(), wallet_name)
+
+    @pyqtSlot(str, result=bool)
+    def isValidNewWalletName(self, wallet_name: str) -> bool:
+        if not wallet_name:
+            return False
+        if self._qedaemon.availableWallets.wallet_name_exists(wallet_name):
+            return False
+        wallet_path = self._wallet_path_from_wallet_name(wallet_name)
+        # note: we should probably restrict wallet names to be alphanumeric (plus underscore, etc)...
+        #       wallet_name might contain ".." (etc) and hence sketchy path traversals are possible.
+        #       Anyway, this at least validates that the path looks sane to the filesystem:
+        try:
+            temp_storage = WalletStorage(wallet_path)
+        except (StorageReadWriteError, WalletFileException) as e:
+            return False
+        except Exception as e:
+            self._logger.exception("")
+            return False
+        if temp_storage.file_exists():
+            return False
+        return True
+
     @pyqtSlot('QJSValue', bool, str)
     def createStorage(self, js_data, single_password_enabled, single_password):
         self._logger.info('Creating wallet from wizard data')
@@ -125,7 +151,7 @@ class QENewWalletWizard(NewWalletWizard, QEAbstractWizard):
             data['encrypt'] = True
             data['password'] = single_password
 
-        path = os.path.join(os.path.dirname(self._qedaemon.daemon.config.get_wallet_path()), data['wallet_name'])
+        path = self._wallet_path_from_wallet_name(data['wallet_name'])
 
         try:
             self.create_storage(path, data)