Enable AppFocus and AppBlur in terminal emulators

src/textual/_xterm_parser.py

@@ -20,6 +20,8 @@
 )
 _re_bracketed_paste_start = re.compile(r"^\x1b\[200~$")
 _re_bracketed_paste_end = re.compile(r"^\x1b\[201~$")
+_re_focusin = re.compile(r"^\x1b\[I$")
+_re_focusout = re.compile(r"^\x1b\[O$")
 
 
 class XTermParser(Parser[events.Event]):
@@ -202,6 +204,14 @@ def reissue_sequence_as_keys(reissue_sequence: str) -> None:
 
                     self.debug_log(f"sequence={sequence!r}")
 
+                    if _re_focusin.match(sequence):
+                        on_token(events.AppFocus())
+                        break
+
+                    if _re_focusout.match(sequence):
+                        on_token(events.AppBlur())
+                        break
+
                     bracketed_paste_start_match = _re_bracketed_paste_start.match(
                         sequence
                     )

src/textual/drivers/linux_driver.py

@@ -232,6 +232,7 @@ def on_terminal_resize(signum, stack) -> None:
 
         self.write("\x1b[?25l")  # Hide cursor
         self.write("\033[?1003h\n")
+        self.write("\033[?1004h\n")  # Enable FocusIn/FocusOut.
         self.flush()
         self._key_thread = Thread(target=self._run_input_thread)
         send_size_event()
@@ -316,6 +317,7 @@ def stop_application_mode(self) -> None:
 
             # Alt screen false, show cursor
             self.write("\x1b[?1049l" + "\x1b[?25h")
+            self.write("\033[?1004l\n")  # Disable FocusIn/FocusOut.
             self.flush()
 
     def close(self) -> None: