From 682fb7108cc999466821698ac035ea40d1797811 Mon Sep 17 00:00:00 2001
From: Dean Scarff <dos@scarff.id.au>
Date: Sun, 26 Jul 2020 06:32:12 +1000
Subject: [PATCH] Fix flaky unshifting

---
 quantum/process_keycode/process_auto_shift.c | 36 +++++++++++++-------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/quantum/process_keycode/process_auto_shift.c b/quantum/process_keycode/process_auto_shift.c
index c6c9658fddf8..373e087cf1d8 100644
--- a/quantum/process_keycode/process_auto_shift.c
+++ b/quantum/process_keycode/process_auto_shift.c
@@ -46,7 +46,7 @@ void autoshift_timer_report(void) {
     send_string((const char *)display);
 }
 
-/** \brief Resets the autoshift state and releases the shift key */
+/** \brief Resets the autoshift state */
 static void autoshift_flush(uint16_t now) {
     if (autoshift_flags.in_progress && !autoshift_flags.registered) {
         // Register the key.
@@ -54,17 +54,22 @@ static void autoshift_flush(uint16_t now) {
 #    if TAP_CODE_DELAY > 0
         wait_ms(TAP_CODE_DELAY);
 #    endif
-    } else if (autoshift_flags.holding_shift) {
-        // Release the shift key if it was simulated.
-        unregister_code(KC_LSFT);
     }
     // Roll the autoshift_time forward for detecting tap-and-hold.
     autoshift_time                = now;
     autoshift_flags.in_progress   = false;
-    autoshift_flags.holding_shift = false;
     autoshift_flags.registered    = false;
 }
 
+/** \brief Releases the shift key if it was held by auto-shift */
+static void autoshift_flush_shift(void) {
+    if (autoshift_flags.holding_shift) {
+        // Release the shift key if it was simulated.
+        unregister_code(KC_LSFT);
+    }
+    autoshift_flags.holding_shift = false;
+}
+
 /** \brief Record the press of an autoshiftable key
  *
  *  \return Whether the record should be further processed.
@@ -74,16 +79,14 @@ static bool autoshift_press(uint16_t keycode, keyrecord_t *record) {
         return true;
     }
 
+    const uint16_t elapsed = TIMER_DIFF_16(record->event.time, autoshift_time);
     autoshift_flush(record->event.time);
 
 #    ifndef AUTO_SHIFT_MODIFIERS
-    if (get_mods()) {
+    if (get_mods() ^ (autoshift_flags.holding_shift ? MOD_BIT(KC_LSFT) : 0)) {
         return true;
     }
 #    endif
-
-    const uint16_t elapsed = TIMER_DIFF_16(record->event.time, autoshift_time);
-
 #    ifndef TAPPING_FORCE_HOLD
     if (elapsed < TAPPING_TERM && keycode == autoshift_lastkey && !autoshift_flags.lastshifted) {
         // Allow a tap-then-hold to hold the unshifted key.
@@ -93,7 +96,6 @@ static bool autoshift_press(uint16_t keycode, keyrecord_t *record) {
 #    endif
 
     // Record the keycode so we can simulate it later.
-    autoshift_time              = record->event.time;
     autoshift_lastkey           = keycode;
     autoshift_flags.in_progress = true;
 
@@ -146,15 +148,16 @@ static void autoshift_check_record(uint16_t keycode, keyrecord_t *record) {
 
     // Process the release of the autoshiftable key.
     if (keycode == autoshift_lastkey && !record->event.pressed) {
+        autoshift_flush_shift();
         // Time since the initial press was recorded.
         const uint16_t elapsed = TIMER_DIFF_16(record->event.time, autoshift_time);
         if (!autoshift_flags.registered && elapsed < autoshift_timeout) {
-            autoshift_flags.lastshifted = false;
             // Auto-shiftable key is being released before the shift timeout;
             // simulate the original press then let the usual processing take
             // care of the release.
             register_code(keycode);
-            autoshift_flags.registered = true;
+            autoshift_flags.lastshifted = false;
+            autoshift_flags.registered  = true;
 #    if TAP_CODE_DELAY > 0
             wait_ms(TAP_CODE_DELAY);
 #    endif
@@ -167,9 +170,13 @@ static void autoshift_check_record(uint16_t keycode, keyrecord_t *record) {
             autoshift_flags.holding_shift = false;
         } else if (!autoshift_flags.registered) {
             // If the key isn't registered yet, it means the timeout hasn't
-            // elapsed, so register the unshifted key.
+            // elapsed, so register the key without additional shifting.
             autoshift_flush(0);
             autoshift_lastkey = KC_NO;
+        } else {
+            // The key is registered; flush any shift state for the
+            // non-autoshiftable key.
+            autoshift_flush_shift();
         }
     }
 }
@@ -190,17 +197,20 @@ void autoshift_matrix_scan(void) {
 
 void autoshift_enable(void) {
     autoshift_flags.enabled = true;
+    autoshift_flush_shift();
     autoshift_flush(0);
 }
 
 void autoshift_disable(void) {
     autoshift_flags.enabled = false;
+    autoshift_flush_shift();
     autoshift_flush(0);
 }
 
 void autoshift_toggle(void) {
     if (autoshift_flags.enabled) {
         autoshift_flags.enabled = false;
+        autoshift_flush_shift();
         autoshift_flush(0);
     } else {
         autoshift_flags.enabled = true;