Export Watch only missing .dat file extension #956

When exporting a watchonly wallet using the GUI the .dat extension is not automatically added to the file. The GUI then is not able to restore a wallet without the explicit .dat extension.

~Note: I did not check if this also happens using RPC, will update the issue when tested.~ Edit: The RPC is unaffected by this, it does allow non .dat files.

With .dat works:

<img width="1024" height="705" alt="Image" src="https://github.com/user-attachments/assets/12c8b3fa-da54-4a4c-944d-c84bdd8d1361" />

Without .dat does not see it:

<img width="1022" height="698" alt="Image" src="https://github.com/user-attachments/assets/97b65440-33ef-44db-a514-70aec2f526c9" />

This is fixed in https://github.com/bitcoin-core/gui/pull/957

When exporting a watchonly wallet using the GUI the .dat extension is not automatically added to the file.

The GUI behaviour is consistent with the RPC.

The GUI then is not able to restore a wallet without the explicit .dat extension.

Perhaps we could provide the user with a hint?

The GUI behaviour is consistent with the RPC.

For the export part I think so, but for importing, it does allow importing non .dat files. While the GUI does not show them.

Perhaps we could provide the user with a hint?

Maybe we could allow importing non .dat file too. If the file is not a wallet backup, the import should just fail.