Honestly, I think that maybe we should add a message if both bluetooth and NKRO are enabled, so it's obvious at build time. Not a hard error, but something so users can see it.

A warning like that probably would have saved me more time than if it were only in the documentation, I like that. I can try to tackle that, but I don't feel confident in being able to make the change correctly and test it.

in lufa.c:

    if ((where == OUTPUT_BLUETOOTH || where == OUTPUT_USB_AND_BT) && keymap_config.nkro) {
        print("Both Bluetooth output and NKRO are enabled. This will cause errors in Bluetooth output.\n");
    }
    if ((where == OUTPUT_BLUETOOTH || where == OUTPUT_USB_AND_BT) && !keymap_config.nkro) {
#    ifdef MODULE_ADAFRUIT_BLE

Or is there somewhere earlier on in the build process where the rules are checked and the warning could be surfaced there?

That print() will not work unless the Console feature is enabled, and you are looking at the output in QMK Toolbox or hid_listen.
Something like the following in tmk_core/common.mk should do the trick:

ifeq ($(strip $(NKRO_ENABLE)), yes)
    ifeq ($(PROTOCOL), VUSB)
        $(info NKRO is not currently supported on V-USB, and has been disabled.)
    else ifeq ($(strip $(BLUETOOTH_ENABLE), yes))
        $(info NKRO is not currently supported with Bluetooth, and has been disabled.)
    else ifneq ($(BLUETOOTH),)
        $(info NKRO is not currently supported with Bluetooth, and has been disabled.)
    else
        TMK_COMMON_DEFS += -DNKRO_ENABLE
        SHARED_EP_ENABLE = yes
    endif
endif

Updating checklist with changes from af17d3d

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

None

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

Also, thanks for the help @fauxpark and @drashna :)

Just looking around for appearances of keymap_config.nkro, it seems like it is actually possible for this to be set to 1 even if NKRO is not compiled in - neither process_magic.c nor bootmagic.c have #ifdef NKRO_ENABLE guards around their NKRO-related code.

On further inspection my above comment is incorrect, as when NKRO_ENABLE = no none of the code which checks keymap_config.nkro will be compiled in anyway. Maybe it's worth adding ifdefs around the bootmagic/magic NKRO stuff too to save a couple tens of bytes, but for now I'm happy with this. Thanks a lot!

Excellent, thanks @fauxpark!

I think NKRO should not be disabled on Build. I mean, I’m using my keyboard wired and on Bluetooth. When I connect it to Bluetooth I boot with bootmagic to disable nkro, and then when I go wired I enable it.

@fauxpark , do you think there would be a way to have NKRO enabled for wired mode while disabling it in Bluetooth mode?