[KBM] Allow users to map only modifier key shortcuts

[OscarPalafox]

Summary of the new feature/enhancement

Right now, if we try to set either the original shortcut or the new shortcut to finish on a modifier key (Ctrl, Shift, Alt, Win), the error message "Some of the keys could not be remapped. Do you want to continue anyway?" appears. Allowing users to remap shortcuts that end with a modifier key would allow users to have a bigger pool of shortcuts to modify (e.g. changing input keyboard layouts and input languages).

Proposed technical implementation details (optional)

[saahmedm]

This is a good idea, it would require us to change the logic in that those shortcuts would only apply on release. Adding this to suggested ideas, it may fall outside of v1 scope but on our minds!

[volcbs]

@enricogior
Answering your question in #5670, the user scenario would be something like you want to use windows + space for running powertoys run, but at the same time you want to be able to switch language that is originally either be accessed via windows + space or alt (left) + shift. However, you want to access it via ctrl + space so you want it to remap alt (left) + shift. I guess something like that?

[MailYouLater]

Hello. I'd like to add my voice here to say that modifier only shortcut key remapping is one of the main things I hope for every time I update PowerToys. Please add this.
Also, yes. I agree that remaps of modifier only keyboard shortcuts should activate on key-up instead of key-down. This is also how the modifier key only keyboard functionalities that are built into Windows operate (e.g. pressing and releasing the Win key opens the Start menu, which occurs when you let go of the Win key without having pressed any other keys after pressing it down).

[microsoftmatt]

#19936 describes another user scenario for this feature

[msidnin]

My scenario:
I want to remap [CapsLock] to [Shift + Alt] in Windows to switch a language in one action, not using [Win+Space] + [Manual Selection].
"Keyboard Manager" is the closest application to this goal, but it can't map modifiers-only shortcuts like [Alt+Shift]. There is a key in the dropdown named "Undefined" but [Alt+Shift+Undefined] doesn't work either.

There are alternatives and none of them is ok:

• I may use [`] key to switch languages and remap [CapsLock] -> [`]. But I can't lose "`" symbol because it's used for code formatting
• AutoHotkey adds a lag, unreliable, often blocked by security soft
• Keyboards soft. Mine (Logitech) allows only to remap functional and special keys.
• Untrusted soft. It's untrusted *.exe files and I won't run them.