Minimal working example for qmk_firmware hold+tap dual key modifications

mwe.c

// Demonstrates how to use double keys
// hold q = 1, tap q = q
// hold Q = !, tap Q = Q
//
// hold shift = shift, tap shift = ~
// hold ctrl  = ctrl, tap ctrl = !


#include "planck.h"
#include "timer.h"  // Have to include timer for timer_read and timer_elapsed

#define ____       KC_NO  // Just for easy reading
#define COLMAK     0

//      Macros with human readable name
#define HOLD_1_TAP_Q             10
#define HOLD_SHIFT_TAP_TILDE          20
#define HOLD_CTRL_TAP_EXLAMATION_MARK 21

const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
[COLMAK] = {
  /* ---------------------------------------------------------------------------
  * |  esc  |  q  |  w  |  f  |  p  |  g  |  j  |  l  |  u  |  y  |  ;  | bspc|
  * |-------------------------------------------------------------------------|
  * |  tab  |  a  |  r  |  s  |  t  |  d  |  h  |  n  |  e  |  i  |  o  |enter|
  * |-------------------------------------------------------------------------|
  * | shift |  z  |  x  |  c  |  v  |  b  |  k  |  m  |  ,  |  .  |  /  |  `  |
  * |-------------------------------------------------------------------------|
  * |  ctrl | opt | cmd | fn |lower|    space   |raise|left |down | up  |right|
  * -------------------------------------------------------------------------*/
  {MEH_T(KC_ESC), M(10),   KC_W,    KC_F, KC_P,  KC_G,   KC_J,   KC_L,  KC_U,    KC_Y,    KC_M,    KC_BSPC},
  {ALL_T(KC_TAB), KC_A,    KC_R,    KC_S, KC_T,  KC_D,   KC_H,   KC_N,  KC_E,    KC_I,    KC_O,    LCAG_T(KC_ENT)},
  {M(20),         KC_Z,    KC_X,    KC_C, KC_V,  KC_B,   KC_K,   KC_M,  KC_COMM, KC_DOT,  KC_SLSH, SFT_T(KC_GRAVE)},
  {M(21),         KC_LALT, KC_LGUI, ____, ____,  KC_SPC, KC_SPC, RESET, KC_LEFT, KC_DOWN, KC_UP,   KC_RGHT}
},
};

const uint16_t PROGMEM fn_actions[] = {
};

// Put everything inside the action macros function in the base template
const macro_t *action_get_macro(keyrecord_t *record, uint8_t id, uint8_t opt)
{
// This will hold the timestamp of when we start holding the key
static uint16_t start;
switch(id) {
  // When we hit our new macro
  case HOLD_1_TAP_Q:
    // On keydown, start the timer
    if (record->event.pressed) {
      start = timer_read();
      // Start holding the button (with placeholder "NO"-key)
      return MACRO(D(NO), END);
    } else {
      // On key up
      // If time was greater than 150ms, it was a hold
      if (timer_elapsed(start) > 150) {
        // Trigger macro for exclamation mark
        return MACRO(T(1), END);
      } else {
        // Otherwise it was a tap, put letter q
        // and release the shift key
        return MACRO(T(Q), END);
      }
    }
    break;
  case HOLD_SHIFT_TAP_TILDE:
    // On keydown, start the timer
    if (record->event.pressed) {
      start = timer_read();
      // Start holding shift
      return MACRO(D(LSFT), END);
    } else {
      // On key up
      // If time was greater than 150ms, it was a hold
      if (timer_elapsed(start) > 150) {
        // Only release the shift key
        return MACRO(U(LSFT), END);
      } else {
        // Otherwise it was a tap, put in a tilde (since shift is still held)
        // and release the shift key
        return MACRO(T(GRV), U(LSFT), END);
      }
    }
    break;
  case HOLD_CTRL_TAP_EXLAMATION_MARK:
    // On keydown, start the timer
    if (record->event.pressed) {
      start = timer_read();
      // Start holding control
      return MACRO(D(LCTL), END);
    } else {
      // On key up
      // If time was greater than 150ms, it was a hold
      if (timer_elapsed(start) > 150) {
        // Only release the control key
        return MACRO(U(LCTL), END);
      } else {
        // Otherwise it was a tap, put in a exclamation mark.
        // Since control is still held release the control key,
        // and hold shift, press 1, realease shift
        return MACRO(U(LCTL), D(LSFT), T(1), U(LSFT), END);
      }
    }
    break;
}
};