Bug: Context Menu: Dotfiles fail to launch or display "Open with" submenu depending on association count #18493

Description

The Files app fails to open dotfiles (files with an empty base name, like .Rhistory) or trigger the "Open with" dialog, and the behavior changes depending on the number of active file associations in the system.

Expected behavior

• Double-clicking a dotfile with a default association should launch the file in the default app.
• Clicking "Open with" on a dotfile with 0 or 1 association should trigger the Windows OpenWith.exe dialog or correctly expand the submenu.

Actual behavior
The Files app completely fails to open dotfiles or launch the "Open with" dialog unless there are two or more active app associations for that specific extension.

Additional context

• The root cause is strictly tied to files lacking a base name (no characters before the dot).
• Native Windows Explorer handles all these scenarios correctly.
• CLI execution (OpenWith.exe C:\path\to\.testext) works perfectly, regardless of the current amount of active file associations.
• This indicates the bug lies within the Files app's parsing logic for empty base names, which breaks both the default launch action and the fallback OpenWith.exe trigger.

Steps To Reproduce

1. Create a file with no base name (e.g., .testext).
2. Scenario A (0 associations): Right-click and select "Open with". The menu does not open, nor does it trigger the native OpenWith.exe dialog.
3. Scenario B (1 default association): Double-click the file. It fails to open. Right-click and select "Open with". The submenu fails to expand.
4. Scenario C (2+ active associations): Right-click and select "Open with". The submenu successfully expands, making this the only way to open the dotfile via the Files app UI.

Files Version

4.1.1.0

Windows Version

10.0.26100.8457

User ID

18075659-2025-41af-9a75-06ace8d42180

Log File

debug.log