SHIFT_HELD is only put in flags if the key in question is LSHIFT(Key_Something). Otherwise Shift is just a regular key held together with the rest. Well, mostly… we do send modifiers in a separate part of the report, but if shift is held, that does not appear in other keys’ .flags.
.flags is there to differentiate between normal keys and special keys that are only meaningful to the keyboard, such as the modifier-augmented ones, mouse keys, macros, layer keys, and so on.
While not a particularly nice or recommended API, you can look at Keyboard.lastKeyReport.modifiers. If it is non-zero, then the previous report cycle had modifiers. You can also look at Keyboard.keyReport.modifiers for the current report, but depending on where the scanner is in the scanning process, this might not be entirely up-to-date.
Can you file a bug on Kaleidoscope, requesting a proper API to discover all held modifiers?
Can do. If it’s just going to follow the pattern of the existing wasModifierKeyActive() function, I can also submit a PR (sometime this evening).
EDIT: Also, how stable is the order of the bitmap in Keyboard.lastKeyReport.modifiers? I ask, because I also need to find out if any modifiers other than shift are active. I can easily do this in a single line of code by applying a mask:
return Keyboard.lastKeyReport.modifiers & B11011101; // Running off of memory; not at my computer right now
It’s kind of an icky way of doing it, but it’s certainly fast. If the positions in the bit field are likely to change, however, I won’t do it.
The order of modifiers is set in stone, from bit 0 to 8, it is Left Control, Left Shift, Left Alt, Left Gui, Right Control, Right Shift, Right Alt, Right Gui.
It might make sense to introduce a helper, that would build us a mask. Say, kaleidoscope::hid::modifierBitMask(Key_LeftControl, Key_LeftShift) would return (1 << 0) | (1 << 1). This is doable with a little bit of templating, but a PR without this is just as good. The intended use is:
// assuming we're in the kaleidoscope::hid namespace
// return true-ish if Ctrl+Shift was held
return lastActiveModifiers() & modifierBitMask(Key_LeftControl, Key_LeftShift);
Another option is to have #defines for the various modifiers, stuff one could OR together, but I failed to come up with a good name for those, so went with the helper instead.