Fix pressing two keys with the same keycode but different modifiers (#2710)

* Fix extra keyboard report during test_fixture teardown

* Add tests for pressing two keys with only different modifers

* Fix #1708

When two keys that use the same keycode, but different modifiers were
pressed at the same time, the second keypress wasn't registered. This is
fixed by forcing a key release when we detect a new press for the same
keycode.

* Fix the NKRO version of is_key_pressed

* Fix uninitalized loop variable

Co-authored-by: Jack Humbert <jack.humb@gmail.com>

tmk_core/common/action.c

@@ -754,6 +754,13 @@ void register_code(uint8_t code) {
 */
 #endif
             {
+                // Force a new key press if the key is already pressed
+                // without this, keys with the same keycode, but different
+                // modifiers will be reported incorrectly, see issue #1708
+                if (is_key_pressed(keyboard_report, code)) {
+                  del_key(code);
+                  send_keyboard_report();
+                }
                 add_key(code);
                 send_keyboard_report();
             }

tmk_core/common/report.c

@@ -68,6 +68,32 @@ uint8_t get_first_key(report_keyboard_t* keyboard_report) {
 #endif
 }
 
+/** \brief Checks if a key is pressed in the report
+ *
+ * Returns true if the keyboard_report reports that the key is pressed, otherwise false
+ * Note: The function doesn't support modifers currently, and it returns false for KC_NO
+ */
+bool is_key_pressed(report_keyboard_t* keyboard_report, uint8_t key) {
+  if (key == KC_NO) {
+    return false;
+  }
+#ifdef NKRO_ENABLE
+  if (keyboard_protocol && keymap_config.nkro) {
+    if ((key>>3) < KEYBOARD_REPORT_BITS) {
+        return keyboard_report->nkro.bits[key>>3] & 1<<(key&7);
+    } else {
+      return false;
+    }
+  }
+#endif
+  for (int i=0; i < KEYBOARD_REPORT_KEYS; i++) {
+      if (keyboard_report->keys[i] == key) {
+          return true;
+      }
+  }
+  return false;
+}
+
 /** \brief add key byte
  *
  * FIXME: Needs doc

tmk_core/common/report.h

@@ -19,6 +19,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define REPORT_H
 
 #include <stdint.h>
+#include <stdbool.h>
 #include "keycode.h"
 
 /* report id */
@@ -236,6 +237,7 @@ static inline uint16_t KEYCODE2CONSUMER(uint8_t key) {
 
 uint8_t has_anykey(report_keyboard_t* keyboard_report);
 uint8_t get_first_key(report_keyboard_t* keyboard_report);
+bool is_key_pressed(report_keyboard_t* keyboard_report, uint8_t key);
 
 void add_key_byte(report_keyboard_t* keyboard_report, uint8_t code);
 void del_key_byte(report_keyboard_t* keyboard_report, uint8_t code);