Implement progressive enhancement of key event reporting

kitty_tests/screen.py

@@ -728,6 +728,49 @@ class TestScreen(BaseTest):
         self.ae(str(s.linebuf), '0\n5\n6\n7\n\n')
         self.ae(str(s.historybuf), '')
 
+    def test_key_encoding_flags_stack(self):
+        s = self.create_screen()
+        c = s.callbacks
+
+        def w(code, p1='', p2=''):
+            p = f'{p1}'
+            if p2:
+                p += f';{p2}'
+            return parse_bytes(s, f'\033[{code}{p}u'.encode('ascii'))
+
+        def ac(flags):
+            parse_bytes(s, '\033[?u'.encode('ascii'))
+            self.ae(c.wtcbuf, f'\033[?{flags}u'.encode('ascii'))
+            c.clear()
+
+        ac(0)
+        w('=', 0b1001)
+        ac(0b1001)
+        w('=', 0b0011, 2)
+        ac(0b1011)
+        w('=', 0b0110, 3)
+        ac(0b1001)
+        s.reset()
+        ac(0)
+
+        w('>', 0b0011)
+        ac(0b0011)
+        w('=', 0b1111)
+        ac(0b1111)
+        w('>', 0b10)
+        ac(0b10)
+        w('<')
+        ac(0b1111)
+        for i in range(10):
+            w('<')
+            ac(0)
+        s.reset()
+
+        for i in range(1, 16):
+            w('>', i)
+        ac(15)
+        w('<'), ac(14), w('<'), ac(13)
+
     def test_color_stack(self):
         s = self.create_screen()
         c = s.callbacks