Add Retro Shift (Auto Shift for Tap Hold via Retro Tapping) and Custom Auto Shifts (#11059)

* Add Retro Shift and Custom Auto Shifts

* Fix compilation errors with no RETRO_SHIFT value

4 files changed, 455 insertions, 111 deletions

diff --git a/quantum/action.c b/quantum/action.c
index ceaaa551f5..5e81efb671 100644
--- a/quantum/action.c
+++ b/quantum/action.c
@@ -45,10 +45,14 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 int tp_buttons;
 
-#if defined(RETRO_TAPPING) || defined(RETRO_TAPPING_PER_KEY)
+#if defined(RETRO_TAPPING) || defined(RETRO_TAPPING_PER_KEY) || (defined(AUTO_SHIFT_ENABLE) && defined(RETRO_SHIFT))
 int retro_tapping_counter = 0;
 #endif
 
+#if defined(AUTO_SHIFT_ENABLE) && defined(RETRO_SHIFT) && !defined(NO_ACTION_TAPPING)
+#    include "process_auto_shift.h"
+#endif
+
 #ifdef IGNORE_MOD_TAP_INTERRUPT_PER_KEY
 __attribute__((weak)) bool get_ignore_mod_tap_interrupt(uint16_t keycode, keyrecord_t *record) { return false; }
 #endif
@@ -69,7 +73,7 @@ void action_exec(keyevent_t event) {
         dprint("EVENT: ");
         debug_event(event);
         dprintln();
-#if defined(RETRO_TAPPING) || defined(RETRO_TAPPING_PER_KEY)
+#if defined(RETRO_TAPPING) || defined(RETRO_TAPPING_PER_KEY) || (defined(AUTO_SHIFT_ENABLE) && defined(RETRO_SHIFT))
         retro_tapping_counter++;
 #endif
     }
@@ -106,6 +110,11 @@ void action_exec(keyevent_t event) {
 #endif
 
 #ifndef NO_ACTION_TAPPING
+#    if defined(AUTO_SHIFT_ENABLE) && defined(RETRO_SHIFT)
+    if (event.pressed) {
+        retroshift_poll_time(&event);
+    }
+#    endif
     if (IS_NOEVENT(record.event) || pre_process_record_quantum(&record)) {
         action_tapping_process(record);
     }
@@ -730,7 +739,7 @@ void process_action(keyrecord_t *record, action_t action) {
 #endif
 
 #ifndef NO_ACTION_TAPPING
-#    if defined(RETRO_TAPPING) || defined(RETRO_TAPPING_PER_KEY)
+#    if defined(RETRO_TAPPING) || defined(RETRO_TAPPING_PER_KEY) || (defined(AUTO_SHIFT_ENABLE) && defined(RETRO_SHIFT))
     if (!is_tap_action(action)) {
         retro_tapping_counter = 0;
     } else {
@@ -747,7 +756,11 @@ void process_action(keyrecord_t *record, action_t action) {
                     get_retro_tapping(get_event_keycode(record->event, false), record) &&
 #        endif
                     retro_tapping_counter == 2) {
+#        if defined(AUTO_SHIFT_ENABLE) && defined(RETRO_SHIFT)
+                    process_auto_shift(action.layer_tap.code, record);
+#        else
                     tap_code(action.layer_tap.code);
+#        endif
                 }
                 retro_tapping_counter = 0;
             }
diff --git a/quantum/action_tapping.c b/quantum/action_tapping.c
index 60e56fb811..0586fad421 100644
--- a/quantum/action_tapping.c
+++ b/quantum/action_tapping.c
@@ -44,6 +44,10 @@ __attribute__((weak)) bool get_permissive_hold(uint16_t keycode, keyrecord_t *re
 __attribute__((weak)) bool get_hold_on_other_key_press(uint16_t keycode, keyrecord_t *record) { return false; }
 #    endif
 
+#    if defined(AUTO_SHIFT_ENABLE) && defined(RETRO_SHIFT)
+#        include "process_auto_shift.h"
+#    endif
+
 static keyrecord_t tapping_key                         = {};
 static keyrecord_t waiting_buffer[WAITING_BUFFER_SIZE] = {};
 static uint8_t     waiting_buffer_head                 = 0;
@@ -107,12 +111,29 @@ void action_tapping_process(keyrecord_t record) {
 /* return true when key event is processed or consumed. */
 bool process_tapping(keyrecord_t *keyp) {
     keyevent_t event = keyp->event;
+#    if (defined(AUTO_SHIFT_ENABLE) && defined(RETRO_SHIFT)) || defined(TAPPING_TERM_PER_KEY) || defined(PERMISSIVE_HOLD_PER_KEY) || defined(TAPPING_FORCE_HOLD_PER_KEY) || defined(HOLD_ON_OTHER_KEYPRESS_PER_KEY)
+    uint16_t tapping_keycode = get_record_keycode(&tapping_key, false);
+#    endif
 
     // if tapping
     if (IS_TAPPING_PRESSED()) {
-        if (WITHIN_TAPPING_TERM(event)) {
+        // clang-format off
+        if (WITHIN_TAPPING_TERM(event)
+#    if defined(AUTO_SHIFT_ENABLE) && defined(RETRO_SHIFT)
+            || (
+#        ifdef RETRO_TAPPING_PER_KEY
+                get_retro_tapping(tapping_keycode, keyp) &&
+#        endif
+                (RETRO_SHIFT + 0) != 0 && TIMER_DIFF_16(event.time, tapping_key.event.time) < (RETRO_SHIFT + 0)
+            )
+#    endif
+        ) {
+            // clang-format on
             if (tapping_key.tap.count == 0) {
                 if (IS_TAPPING_RECORD(keyp) && !event.pressed) {
+#    if defined(AUTO_SHIFT_ENABLE) && defined(RETRO_SHIFT)
+                    retroshift_swap_times();
+#    endif
                     // first tap!
                     debug("Tapping: First tap(0->1).\n");
                     tapping_key.tap.count = 1;
@@ -128,22 +149,70 @@ bool process_tapping(keyrecord_t *keyp) {
                  * This can register the key before settlement of tapping,
                  * useful for long TAPPING_TERM but may prevent fast typing.
                  */
-#    if defined(TAPPING_TERM_PER_KEY) || (TAPPING_TERM >= 500) || defined(PERMISSIVE_HOLD) || defined(PERMISSIVE_HOLD_PER_KEY)
-                else if (((
+                // clang-format off
+#    if defined(TAPPING_TERM_PER_KEY) || (TAPPING_TERM >= 500) || defined(PERMISSIVE_HOLD) || defined(PERMISSIVE_HOLD_PER_KEY) || (defined(AUTO_SHIFT_ENABLE) && defined(RETRO_SHIFT))
+                else if (
+                    (
+                        (
+                            (
 #        ifdef TAPPING_TERM_PER_KEY
-                              get_tapping_term(get_record_keycode(&tapping_key, false), keyp)
+                                get_tapping_term(tapping_keycode, keyp)
 #        else
-                              TAPPING_TERM
+                                TAPPING_TERM
 #        endif
-                              >= 500)
+                                >= 500
+                            )
 
 #        ifdef PERMISSIVE_HOLD_PER_KEY
-                          || get_permissive_hold(get_record_keycode(&tapping_key, false), keyp)
+                            || get_permissive_hold(tapping_keycode, keyp)
 #        elif defined(PERMISSIVE_HOLD)
-                          || true
+                            || true
+#        endif
+                        ) && IS_RELEASED(event) && waiting_buffer_typed(event)
+                    )
+                    // Causes nested taps to not wait past TAPPING_TERM/RETRO_SHIFT
+                    // unnecessarily and fixes them for Layer Taps.
+#        if defined(AUTO_SHIFT_ENABLE) && defined(RETRO_SHIFT)
+                    || (
+#            ifdef RETRO_TAPPING_PER_KEY
+                        get_retro_tapping(tapping_keycode, keyp) &&
+#            endif
+                        (
+                            // Rolled over the two keys.
+                            (
+                                (
+                                    false
+#            if defined(HOLD_ON_OTHER_KEYPRESS) || defined(HOLD_ON_OTHER_KEYPRESS_PER_KEY)
+                                    || (
+                                        IS_LT(tapping_keycode)
+#                ifdef HOLD_ON_OTHER_KEYPRESS_PER_KEY
+                                        && get_hold_on_other_keypress(tapping_keycode, keyp)
+#                endif
+                                    )
+#            endif
+#            if !defined(IGNORE_MOD_TAP_INTERRUPT) || defined(IGNORE_MOD_TAP_INTERRUPT_PER_KEY)
+                                    || (
+                                        IS_MT(tapping_keycode)
+#                ifdef IGNORE_MOD_TAP_INTERRUPT_PER_KEY
+                                        && !get_ignore_mod_tap_interrupt(tapping_keycode, keyp)
+#                endif
+                                    )
+#            endif
+                                ) && tapping_key.tap.interrupted == true
+                            )
+                            // Makes Retro Shift ignore [IGNORE_MOD_TAP_INTERRUPT's
+                            // effects on nested taps for MTs and the default
+                            // behavior of LTs] below TAPPING_TERM or RETRO_SHIFT.
+                            || (
+                                IS_RETRO(tapping_keycode)
+                                && (event.key.col != tapping_key.event.key.col || event.key.row != tapping_key.event.key.row)
+                                && IS_RELEASED(event) && waiting_buffer_typed(event)
+                            )
+                        )
+                    )
 #        endif
-                              ) &&
-                         IS_RELEASED(event) && waiting_buffer_typed(event)) {
+                ) {
+                    // clang-format on
                     debug("Tapping: End. No tap. Interfered by typing key\n");
                     process_record(&tapping_key);
                     tapping_key = (keyrecord_t){};
@@ -181,7 +250,7 @@ bool process_tapping(keyrecord_t *keyp) {
                         tapping_key.tap.interrupted = true;
 #    if defined(HOLD_ON_OTHER_KEY_PRESS) || defined(HOLD_ON_OTHER_KEY_PRESS_PER_KEY)
 #        if defined(HOLD_ON_OTHER_KEY_PRESS_PER_KEY)
-                        if (get_hold_on_other_key_press(get_record_keycode(&tapping_key, false), keyp))
+                        if (get_hold_on_other_key_press(tapping_keycode, keyp))
 #        endif
                         {
                             debug("Tapping: End. No tap. Interfered by pressed key\n");
@@ -284,14 +353,25 @@ bool process_tapping(keyrecord_t *keyp) {
             }
         }
     } else if (IS_TAPPING_RELEASED()) {
-        if (WITHIN_TAPPING_TERM(event)) {
+        // clang-format off
+        if (WITHIN_TAPPING_TERM(event)
+#    if defined(AUTO_SHIFT_ENABLE) && defined(RETRO_SHIFT)
+            || (
+#        ifdef RETRO_TAPPING_PER_KEY
+                get_retro_tapping(tapping_keycode, keyp) &&
+#        endif
+                (RETRO_SHIFT + 0) != 0 && TIMER_DIFF_16(event.time, tapping_key.event.time) < (RETRO_SHIFT + 0)
+            )
+#    endif
+        ) {
+            // clang-format on
             if (event.pressed) {
                 if (IS_TAPPING_RECORD(keyp)) {
 //#    ifndef TAPPING_FORCE_HOLD
 #    if !defined(TAPPING_FORCE_HOLD) || defined(TAPPING_FORCE_HOLD_PER_KEY)
                     if (
 #        ifdef TAPPING_FORCE_HOLD_PER_KEY
-                        !get_tapping_force_hold(get_record_keycode(&tapping_key, false), keyp) &&
+                        !get_tapping_force_hold(tapping_keycode, keyp) &&
 #        endif
                         !tapping_key.tap.interrupted && tapping_key.tap.count > 0) {
                         // sequential tap.
diff --git a/quantum/process_keycode/process_auto_shift.c b/quantum/process_keycode/process_auto_shift.c
index 4d928edb57..bbc6367ff1 100644
--- a/quantum/process_keycode/process_auto_shift.c
+++ b/quantum/process_keycode/process_auto_shift.c
@@ -18,7 +18,6 @@
 
 #    include <stdbool.h>
 #    include <stdio.h>
-
 #    include "process_auto_shift.h"
 
 #    ifndef AUTO_SHIFT_DISABLED_AT_STARTUP
@@ -27,11 +26,25 @@
 #        define AUTO_SHIFT_STARTUP_STATE false /* disabled */
 #    endif
 
-static uint16_t autoshift_time    = 0;
-static uint16_t autoshift_timeout = AUTO_SHIFT_TIMEOUT;
-static uint16_t autoshift_lastkey = KC_NO;
+// Stores the last Auto Shift key's up or down time, for evaluation or keyrepeat.
+static uint16_t autoshift_time = 0;
+#    if defined(RETRO_SHIFT) && !defined(NO_ACTION_TAPPING)
+// Stores the last key's up or down time, to replace autoshift_time so that Tap Hold times are accurate.
+static uint16_t retroshift_time = 0;
+// Stores a possibly Retro Shift key's up or down time, as retroshift_time needs
+// to be set before the Retro Shift key is evaluated if it is interrupted by an
+// Auto Shifted key.
+static uint16_t last_retroshift_time;
+#    endif
+static uint16_t    autoshift_timeout = AUTO_SHIFT_TIMEOUT;
+static uint16_t    autoshift_lastkey = KC_NO;
+static keyrecord_t autoshift_lastrecord;
+// Keys take 8 bits if modifiers are excluded. This records the shift state
+// when pressed for each key, so that can be passed to the release function
+// and it knows which key needs to be released (if shifted is different base).
+static uint16_t autoshift_shift_states[((1 << 8) + 15) / 16];
 static struct {
-    // Whether autoshift is enabled.
+    // Whether Auto Shift is enabled.
     bool enabled : 1;
     // Whether the last auto-shifted key was released after the timeout.  This
     // is used to replicate the last key for a tap-then-hold.
@@ -40,43 +53,157 @@ static struct {
     bool in_progress : 1;
     // Whether the auto-shifted keypress has been registered.
     bool holding_shift : 1;
-} autoshift_flags = {AUTO_SHIFT_STARTUP_STATE, false, false, false};
+    // Whether the user is holding a shift and we removed it.
+    bool cancelling_lshift : 1;
+    bool cancelling_rshift : 1;
+    // clang-format wants to remove the true for some reason.
+    // clang-format off
+} autoshift_flags = {AUTO_SHIFT_STARTUP_STATE, false, false, false, false, false};
+// clang-format on
+
+/** \brief Called on physical press, returns whether key should be added to Auto Shift */
+__attribute__((weak)) bool get_custom_auto_shifted_key(uint16_t keycode, keyrecord_t *record) { return false; }
+
+/** \brief Called on physical press, returns whether is Auto Shift key */
+__attribute__((weak)) bool get_auto_shifted_key(uint16_t keycode, keyrecord_t *record) {
+    switch (keycode) {
+#    ifndef NO_AUTO_SHIFT_ALPHA
+        case AUTO_SHIFT_ALPHA:
+#    endif
+#    ifndef NO_AUTO_SHIFT_NUMERIC
+        case AUTO_SHIFT_NUMERIC:
+#    endif
+#    ifndef NO_AUTO_SHIFT_SPECIAL
+        case AUTO_SHIFT_SPECIAL:
+#    endif
+            return true;
+    }
+    return get_custom_auto_shifted_key(keycode, record);
+}
+
+/** \brief Called to check whether defines should apply if PER_KEY is set for it */
+__attribute__((weak)) bool get_auto_shift_repeat(uint16_t keycode, keyrecord_t *record) { return true; }
+__attribute__((weak)) bool get_auto_shift_no_auto_repeat(uint16_t keycode, keyrecord_t *record) { return true; }
+
+/** \brief Called when an Auto Shift key needs to be pressed */
+__attribute__((weak)) void autoshift_press_user(uint16_t keycode, bool shifted, keyrecord_t *record) {
+    if (shifted) {
+        add_weak_mods(MOD_BIT(KC_LSFT));
+    }
+    register_code16((IS_RETRO(keycode)) ? keycode & 0xFF : keycode);
+}
+
+/** \brief Called when an Auto Shift key needs to be released */
+__attribute__((weak)) void autoshift_release_user(uint16_t keycode, bool shifted, keyrecord_t *record) { unregister_code16((IS_RETRO(keycode)) ? keycode & 0xFF : keycode); }
+
+/** \brief Sets the shift state to use when keyrepeating, required by custom shifts */
+void set_autoshift_shift_state(uint16_t keycode, bool shifted) {
+    keycode = keycode & 0xFF;
+    if (shifted) {
+        autoshift_shift_states[keycode / 16] |= (uint16_t)1 << keycode % 16;
+    } else {
+        autoshift_shift_states[keycode / 16] &= ~((uint16_t)1 << keycode % 16);
+    }
+}
+
+/** \brief Gets the shift state to use when keyrepeating, required by custom shifts */
+bool get_autoshift_shift_state(uint16_t keycode) {
+    keycode = keycode & 0xFF;
+    return (autoshift_shift_states[keycode / 16] & (uint16_t)1 << keycode % 16) != (uint16_t)0;
+}
+
+/** \brief Restores the shift key if it was cancelled by Auto Shift */
+static void autoshift_flush_shift(void) {
+    autoshift_flags.holding_shift = false;
+    del_weak_mods(MOD_BIT(KC_LSFT));
+    if (autoshift_flags.cancelling_lshift) {
+        autoshift_flags.cancelling_lshift = false;
+        add_mods(MOD_BIT(KC_LSFT));
+    }
+    if (autoshift_flags.cancelling_rshift) {
+        autoshift_flags.cancelling_rshift = false;
+        add_mods(MOD_BIT(KC_RSFT));
+    }
+    send_keyboard_report();
+}
 
 /** \brief Record the press of an autoshiftable key
  *
  *  \return Whether the record should be further processed.
  */
 static bool autoshift_press(uint16_t keycode, uint16_t now, keyrecord_t *record) {
-    if (!autoshift_flags.enabled) {
-        return true;
-    }
-
+    // clang-format off
+    if ((get_mods()
+#    if !defined(NO_ACTION_ONESHOT) && !defined(NO_ACTION_TAPPING)
+            | get_oneshot_mods()
+#    endif
+        ) & (~MOD_BIT(KC_LSFT))
+    ) {
+        // clang-format on
+        // Prevents keyrepeating unshifted value of key after using it in a key combo.
+        autoshift_lastkey = KC_NO;
 #    ifndef AUTO_SHIFT_MODIFIERS
-    if (get_mods()) {
-        return true;
-    }
+        // We can't return true here anymore because custom unshifted values are
+        // possible and there's no good way to tell whether the press returned
+        // true upon release.
+        set_autoshift_shift_state(keycode, false);
+        autoshift_press_user(keycode, false, record);
+#        if !defined(NO_ACTION_ONESHOT) && !defined(NO_ACTION_TAPPING)
+        set_oneshot_mods(get_oneshot_mods() & (~MOD_BIT(KC_LSFT)));
+        clear_oneshot_layer_state(ONESHOT_OTHER_KEY_PRESSED);
+#        endif
+        return false;
 #    endif
-#    ifdef AUTO_SHIFT_REPEAT
-    const uint16_t elapsed = TIMER_DIFF_16(now, autoshift_time);
-#        ifndef AUTO_SHIFT_NO_AUTO_REPEAT
-    if (!autoshift_flags.lastshifted) {
+    }
+
+    // Store record to be sent to user functions if there's no release record then.
+    autoshift_lastrecord               = *record;
+    autoshift_lastrecord.event.pressed = false;
+    autoshift_lastrecord.event.time    = 0;
+    // clang-format off
+#    if defined(AUTO_SHIFT_REPEAT) || defined(AUTO_SHIFT_REPEAT_PER_KEY)
+    if (keycode == autoshift_lastkey &&
+#        ifdef AUTO_SHIFT_REPEAT_PER_KEY
+        get_auto_shift_repeat(autoshift_lastkey, record) &&
 #        endif
-        if (elapsed < TAPPING_TERM && keycode == autoshift_lastkey) {
-            // Allow a tap-then-hold for keyrepeat.
-            if (!autoshift_flags.lastshifted) {
-                register_code(autoshift_lastkey);
-            } else {
-                // Simulate pressing the shift key.
-                add_weak_mods(MOD_BIT(KC_LEFT_SHIFT));
-                register_code(autoshift_lastkey);
-            }
-            return false;
+#        if !defined(AUTO_SHIFT_NO_AUTO_REPEAT) || defined(AUTO_SHIFT_NO_AUTO_REPEAT_PER_KEY)
+        (
+            !autoshift_flags.lastshifted
+#            ifdef AUTO_SHIFT_NO_AUTO_REPEAT_PER_KEY
+            || get_auto_shift_no_auto_repeat(autoshift_lastkey, record)
+#            endif
+        ) &&
+#        endif
+        TIMER_DIFF_16(now, autoshift_time) <
+#        ifdef TAPPING_TERM_PER_KEY
+        get_tapping_term(autoshift_lastkey, record)
+#        else
+        TAPPING_TERM
+#        endif
+    ) {
+        // clang-format on
+        // Allow a tap-then-hold for keyrepeat.
+        if (get_mods() & MOD_BIT(KC_LSFT)) {
+            autoshift_flags.cancelling_lshift = true;
+            del_mods(MOD_BIT(KC_LSFT));
         }
-#        ifndef AUTO_SHIFT_NO_AUTO_REPEAT
+        if (get_mods() & MOD_BIT(KC_RSFT)) {
+            autoshift_flags.cancelling_rshift = true;
+            del_mods(MOD_BIT(KC_RSFT));
+        }
+        // autoshift_shift_state doesn't need to be changed.
+        autoshift_press_user(autoshift_lastkey, autoshift_flags.lastshifted, record);
+        return false;
     }
-#        endif
 #    endif
 
+    // Use physical shift state of press event to be more like normal typing.
+#    if !defined(NO_ACTION_ONESHOT) && !defined(NO_ACTION_TAPPING)
+    autoshift_flags.lastshifted = (get_mods() | get_oneshot_mods()) & MOD_BIT(KC_LSFT);
+    set_oneshot_mods(get_oneshot_mods() & (~MOD_BIT(KC_LSFT)));
+#    else
+    autoshift_flags.lastshifted = get_mods() & MOD_BIT(KC_LSFT);
+#    endif
     // Record the keycode so we can simulate it later.
     autoshift_lastkey           = keycode;
     autoshift_time              = now;
@@ -90,51 +217,70 @@ static bool autoshift_press(uint16_t keycode, uint16_t now, keyrecord_t *record)
 
 /** \brief Registers an autoshiftable key under the right conditions
  *
- * If the autoshift delay has elapsed, register a shift and the key.
+ * If autoshift_timeout has elapsed, register a shift and the key.
  *
- * If the autoshift key is released before the delay has elapsed, register the
+ * If the Auto Shift key is released before the delay has elapsed, register the
  * key without a shift.
+ *
+ * Called on key down with keycode=KC_NO, auto-shifted key up, and timeout.
  */
-static void autoshift_end(uint16_t keycode, uint16_t now, bool matrix_trigger) {
-    // Called on key down with KC_NO, auto-shifted key up, and timeout.
-    if (autoshift_flags.in_progress) {
+static void autoshift_end(uint16_t keycode, uint16_t now, bool matrix_trigger, keyrecord_t *record) {
+    if (autoshift_flags.in_progress && (keycode == autoshift_lastkey || keycode == KC_NO)) {
         // Process the auto-shiftable key.
         autoshift_flags.in_progress = false;
-
-        // Time since the initial press was recorded.
-        const uint16_t elapsed = TIMER_DIFF_16(now, autoshift_time);
-        if (elapsed < autoshift_timeout) {
-            register_code(autoshift_lastkey);
-            autoshift_flags.lastshifted = false;
-        } else {
-            // Simulate pressing the shift key.
-            add_weak_mods(MOD_BIT(KC_LEFT_SHIFT));
-            register_code(autoshift_lastkey);
-            autoshift_flags.lastshifted = true;
-#    if defined(AUTO_SHIFT_REPEAT) && !defined(AUTO_SHIFT_NO_AUTO_REPEAT)
-            if (matrix_trigger) {
-                // Prevents release.
-                return;
-            }
+        // clang-format off
+        autoshift_flags.lastshifted =
+            autoshift_flags.lastshifted
+            || TIMER_DIFF_16(now, autoshift_time) >=
+#    ifdef AUTO_SHIFT_TIMEOUT_PER_KEY
+                get_autoshift_timeout(autoshift_lastkey, record)
+#    else
+                autoshift_timeout
 #    endif
+        ;
+        // clang-format on
+        set_autoshift_shift_state(autoshift_lastkey, autoshift_flags.lastshifted);
+        if (get_mods() & MOD_BIT(KC_LSFT)) {
+            autoshift_flags.cancelling_lshift = true;
+            del_mods(MOD_BIT(KC_LSFT));
+        }
+        if (get_mods() & MOD_BIT(KC_RSFT)) {
+            autoshift_flags.cancelling_rshift = true;
+            del_mods(MOD_BIT(KC_RSFT));
         }
+        autoshift_press_user(autoshift_lastkey, autoshift_flags.lastshifted, record);
 
+        // clang-format off
+#    if (defined(AUTO_SHIFT_REPEAT) || defined(AUTO_SHIFT_REPEAT_PER_KEY)) && (!defined(AUTO_SHIFT_NO_AUTO_REPEAT) || defined(AUTO_SHIFT_NO_AUTO_REPEAT_PER_KEY))
+        if (matrix_trigger
+#        ifdef AUTO_SHIFT_REPEAT_PER_KEY
+            && get_auto_shift_repeat(autoshift_lastkey, record)
+#        endif
+#        ifdef AUTO_SHIFT_NO_AUTO_REPEAT_PER_KEY
+            && !get_auto_shift_no_auto_repeat(autoshift_lastkey, record)
+#        endif
+        ) {
+            // Prevents release.
+            return;
+        }
+#    endif
+        // clang-format on
 #    if TAP_CODE_DELAY > 0
         wait_ms(TAP_CODE_DELAY);
 #    endif
-        unregister_code(autoshift_lastkey);
-        del_weak_mods(MOD_BIT(KC_LEFT_SHIFT));
+
+        autoshift_release_user(autoshift_lastkey, autoshift_flags.lastshifted, record);
+        autoshift_flush_shift();
     } else {
         // Release after keyrepeat.
-        unregister_code(keycode);
+        autoshift_release_user(keycode, get_autoshift_shift_state(keycode), record);
         if (keycode == autoshift_lastkey) {
             // This will only fire when the key was the last auto-shiftable
-            // pressed. That prevents aaaaBBBB then releasing a from unshifting
-            // later Bs (if B wasn't auto-shiftable).
-            del_weak_mods(MOD_BIT(KC_LEFT_SHIFT));
+            // pressed. That prevents 'aaaaBBBB' then releasing a from unshifting
+            // later 'B's (if 'B' wasn't auto-shiftable).
+            autoshift_flush_shift();
         }
     }
-    send_keyboard_report();  // del_weak_mods doesn't send one.
     // Roll the autoshift_time forward for detecting tap-and-hold.
     autoshift_time = now;
 }
@@ -147,24 +293,29 @@ static void autoshift_end(uint16_t keycode, uint16_t now, bool matrix_trigger) {
  */
 void autoshift_matrix_scan(void) {
     if (autoshift_flags.in_progress) {
-        const uint16_t now     = timer_read();
-        const uint16_t elapsed = TIMER_DIFF_16(now, autoshift_time);
-        if (elapsed >= autoshift_timeout) {
-            autoshift_end(autoshift_lastkey, now, true);
+        const uint16_t now = timer_read();
+        if (TIMER_DIFF_16(now, autoshift_time) >=
+#    ifdef AUTO_SHIFT_TIMEOUT_PER_KEY
+            get_autoshift_timeout(autoshift_lastkey, &autoshift_lastrecord)
+#    else
+            autoshift_timeout
+#    endif
+        ) {
+            autoshift_end(autoshift_lastkey, now, true, &autoshift_lastrecord);
         }
     }
 }
 
 void autoshift_toggle(void) {
     autoshift_flags.enabled = !autoshift_flags.enabled;
-    del_weak_mods(MOD_BIT(KC_LEFT_SHIFT));
+    autoshift_flush_shift();
 }
 
 void autoshift_enable(void) { autoshift_flags.enabled = true; }
 
 void autoshift_disable(void) {
     autoshift_flags.enabled = false;
-    del_weak_mods(MOD_BIT(KC_LEFT_SHIFT));
+    autoshift_flush_shift();
 }
 
 #    ifndef AUTO_SHIFT_NO_SETUP
@@ -179,76 +330,158 @@ void autoshift_timer_report(void) {
 
 bool get_autoshift_state(void) { return autoshift_flags.enabled; }
 
-uint16_t get_autoshift_timeout(void) { return autoshift_timeout; }
+uint16_t                       get_generic_autoshift_timeout() { return autoshift_timeout; }
+__attribute__((weak)) uint16_t get_autoshift_timeout(uint16_t keycode, keyrecord_t *record) { return autoshift_timeout; }
 
 void set_autoshift_timeout(uint16_t timeout) { autoshift_timeout = timeout; }
 
 bool process_auto_shift(uint16_t keycode, keyrecord_t *record) {
     // Note that record->event.time isn't reliable, see:
     // https://github.com/qmk/qmk_firmware/pull/9826#issuecomment-733559550
-    const uint16_t now = timer_read();
+    // clang-format off
+    const uint16_t now =
+#    if !defined(RETRO_SHIFT) || defined(NO_ACTION_TAPPING)
+        timer_read()
+#    else
+        (record->event.pressed) ? retroshift_time : timer_read()
+#    endif
+    ;
+    // clang-format on
 
     if (record->event.pressed) {
         if (autoshift_flags.in_progress) {
-            // Evaluate previous key if there is one. Doing this elsewhere is
-            // more complicated and easier to break.
-            autoshift_end(KC_NO, now, false);
+            // Evaluate previous key if there is one.
+            autoshift_end(KC_NO, now, false, &autoshift_lastrecord);
         }
-        // For pressing another key while keyrepeating shifted autoshift.
-        del_weak_mods(MOD_BIT(KC_LEFT_SHIFT));
 
         switch (keycode) {
             case KC_ASTG:
                 autoshift_toggle();
-                return true;
+                break;
             case KC_ASON:
                 autoshift_enable();
-                return true;
+                break;
             case KC_ASOFF:
                 autoshift_disable();
-                return true;
+                break;
 
 #    ifndef AUTO_SHIFT_NO_SETUP
             case KC_ASUP:
                 autoshift_timeout += 5;
-                return true;
+                break;
             case KC_ASDN:
                 autoshift_timeout -= 5;
-                return true;
-
+                break;
             case KC_ASRP:
                 autoshift_timer_report();
-                return true;
+                break;
+#    endif
+        }
+        // If Retro Shift is disabled, possible custom actions shouldn't happen.
+        // clang-format off
+        if (IS_RETRO(keycode)
+#    if defined(RETRO_SHIFT) && !defined(NO_ACTION_TAPPING)
+            // Not tapped or #defines mean that rolls should use hold action.
+            && (
+                record->tap.count == 0
+#        ifdef RETRO_TAPPING_PER_KEY
+                || !get_retro_tapping(keycode, record)
+#        endif
+                || (record->tap.interrupted && (IS_LT(keycode)
+#        if defined(HOLD_ON_OTHER_KEY_PRESS) || defined(HOLD_ON_OTHER_KEY_PRESS_PER_KEY)
+#            ifdef HOLD_ON_OTHER_KEY_PRESS_PER_KEY
+                    ? get_hold_on_other_key_press(keycode, record)
+#            else
+                    ? true
+#            endif
+#        else
+                    ? false
+#        endif
+#        if defined(IGNORE_MOD_TAP_INTERRUPT) || defined(IGNORE_MOD_TAP_INTERRUPT_PER_KEY)
+#            ifdef IGNORE_MOD_TAP_INTERRUPT_PER_KEY
+                    : !get_ignore_mod_tap_interrupt(keycode, record)
+#            else
+                    : false
+#            endif
+#        else
+                    : true
+#        endif
+                ))
+            )
+#    endif
+        ) {
+            // clang-format on
+            autoshift_lastkey = KC_NO;
+            return true;
+        }
+    } else {
+        if (keycode == KC_LSFT) {
+            autoshift_flags.cancelling_lshift = false;
+        } else if (keycode == KC_RSFT) {
+            autoshift_flags.cancelling_rshift = false;
+        }
+        // Same as above (for pressed), additional checks are not needed because
+        // tap.count gets set to 0 in process_action
+        // clang-format off
+        else if (IS_RETRO(keycode)
+#    if defined(RETRO_SHIFT) && !defined(NO_ACTION_TAPPING)
+            && (
+                record->tap.count == 0
+#        ifdef RETRO_TAPPING_PER_KEY
+                || !get_retro_tapping(keycode, record)
+#        endif
+            )
 #    endif
+        ) {
+            // Fixes modifiers not being applied to rolls with AUTO_SHIFT_MODIFIERS set.
+#    if !defined(IGNORE_MOD_TAP_INTERRUPT) || defined(IGNORE_MOD_TAP_INTERRUPT_PER_KEY)
+            if (autoshift_flags.in_progress
+#        ifdef IGNORE_MOD_TAP_INTERRUPT_PER_KEY
+                && !get_ignore_mod_tap_interrupt(keycode, record)
+#        endif
+            ) {
+                autoshift_end(KC_NO, now, false, &autoshift_lastrecord);
+            }
+#    endif
+            // clang-format on
+            return true;
         }
     }
+
+    if (!autoshift_flags.enabled) {
+        return true;
+    }
     if (get_auto_shifted_key(keycode, record)) {
         if (record->event.pressed) {
             return autoshift_press(keycode, now, record);
         } else {
-            autoshift_end(keycode, now, false);
+            autoshift_end(keycode, now, false, record);
             return false;
         }
     }
+
+    // Prevent keyrepeating of older keys upon non-AS key event.
+    // Not commented at above returns but they serve the same function.
+    if (record->event.pressed) {
+        autoshift_lastkey = KC_NO;
+    }
     return true;
 }
 
-__attribute__((weak)) bool get_auto_shifted_key(uint16_t keycode, keyrecord_t *record) {
-    switch (keycode) {
-#    ifndef NO_AUTO_SHIFT_ALPHA
-        case KC_A ... KC_Z:
-#    endif
-#    ifndef NO_AUTO_SHIFT_NUMERIC
-        case KC_1 ... KC_0:
-#    endif
-#    ifndef NO_AUTO_SHIFT_SPECIAL
-        case KC_TAB:
-        case KC_MINUS ... KC_SLASH:
-        case KC_NONUS_BACKSLASH:
-#    endif
-            return true;
+#    if defined(RETRO_SHIFT) && !defined(NO_ACTION_TAPPING)
+// Called to record time before possible delays by action_tapping_process.
+void retroshift_poll_time(keyevent_t *event) {
+    last_retroshift_time = retroshift_time;
+    retroshift_time      = timer_read();
+}
+// Used to swap the times of Retro Shifted key and Auto Shift key that interrupted it.
+void retroshift_swap_times() {
+    if (last_retroshift_time != 0 && autoshift_flags.in_progress) {
+        uint16_t temp        = retroshift_time;
+        retroshift_time      = last_retroshift_time;
+        last_retroshift_time = temp;
     }
-    return false;
 }
+#    endif
 
 #endif
diff --git a/quantum/process_keycode/process_auto_shift.h b/quantum/process_keycode/process_auto_shift.h
index 00a9ab036f..ac6a143746 100644
--- a/quantum/process_keycode/process_auto_shift.h
+++ b/quantum/process_keycode/process_auto_shift.h
@@ -22,13 +22,31 @@
 #    define AUTO_SHIFT_TIMEOUT 175
 #endif
 
+#define IS_LT(kc) ((kc) >= QK_LAYER_TAP && (kc) <= QK_LAYER_TAP_MAX)
+#define IS_MT(kc) ((kc) >= QK_MOD_TAP && (kc) <= QK_MOD_TAP_MAX)
+#define IS_RETRO(kc) (IS_MT(kc) || IS_LT(kc))
+#define DO_GET_AUTOSHIFT_TIMEOUT(keycode, record, ...) record
+// clang-format off
+#define AUTO_SHIFT_ALPHA KC_A ... KC_Z
+#define AUTO_SHIFT_NUMERIC KC_1 ... KC_0
+#define AUTO_SHIFT_SPECIAL          \
+             KC_TAB:                \
+        case KC_MINUS ... KC_SLASH: \
+        case KC_NONUS_BSLASH
+// clang-format on
+
 bool process_auto_shift(uint16_t keycode, keyrecord_t *record);
+void retroshift_poll_time(keyevent_t *event);
+void retroshift_swap_times(void);
 
 void     autoshift_enable(void);
 void     autoshift_disable(void);
 void     autoshift_toggle(void);
 bool     get_autoshift_state(void);
-uint16_t get_autoshift_timeout(void);
+uint16_t get_generic_autoshift_timeout(void);
+// clang-format off
+uint16_t (get_autoshift_timeout)(uint16_t keycode, keyrecord_t *record);
 void     set_autoshift_timeout(uint16_t timeout);
 void     autoshift_matrix_scan(void);
-bool     get_auto_shifted_key(uint16_t keycode, keyrecord_t *record);
+bool     get_custom_auto_shifted_key(uint16_t keycode, keyrecord_t *record);
+// clang-format on