Fixed AttributeError in rl_get_prompt() when prompt is None.

Author: kmvanbrunt

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.3.0 (TBD, 2021)
+* Bug Fixes
+  * Fixed `AttributeError` in `rl_get_prompt()` when prompt is `None`.
+
 ## 2.2.0 (September 14, 2021)
 * Bug Fixes
   * Fixed extra space appended to each alias by "alias list" command

cmd2/cmd2.py

@@ -5011,15 +5011,14 @@ def async_alert(self, alert_msg: str, new_prompt: Optional[str] = None) -> None:
         To the user it appears as if an alert message is printed above the prompt and their current input
         text and cursor location is left alone.
 
-        Raises a `RuntimeError` if called while another thread holds `terminal_lock`.
-
         IMPORTANT: This function will not print an alert unless it can acquire self.terminal_lock to ensure
                    a prompt is onscreen. Therefore it is best to acquire the lock before calling this function
                    to guarantee the alert prints and to avoid raising a RuntimeError.
 
         :param alert_msg: the message to display to the user
         :param new_prompt: If you also want to change the prompt that is displayed, then include it here.
                            See async_update_prompt() docstring for guidance on updating a prompt.
+        :raises RuntimeError: if called while another thread holds `terminal_lock`
         """
         if not (vt100_support and self.use_rawinput):
             return
@@ -5082,8 +5081,6 @@ def async_update_prompt(self, new_prompt: str) -> None:  # pragma: no cover
         prompt, it is best to keep the prompt the same width as what's on screen. Otherwise the user's input text will
         be shifted and the update will not be seamless.
 
-        Raises a `RuntimeError` if called while another thread holds `terminal_lock`.
-
         IMPORTANT: This function will not update the prompt unless it can acquire self.terminal_lock to ensure
                    a prompt is onscreen. Therefore it is best to acquire the lock before calling this function
                    to guarantee the prompt changes and to avoid raising a RuntimeError.
@@ -5093,36 +5090,29 @@ def async_update_prompt(self, new_prompt: str) -> None:  # pragma: no cover
                    line command completes.
 
         :param new_prompt: what to change the prompt to
+        :raises RuntimeError: if called while another thread holds `terminal_lock`
         """
         self.async_alert('', new_prompt)
 
-    def set_window_title(self, title: str) -> None:  # pragma: no cover
-        """Set the terminal window title.
-
-        Raises a `RuntimeError` if called while another thread holds `terminal_lock`.
+    @staticmethod
+    def set_window_title(title: str) -> None:  # pragma: no cover
+        """
+        Set the terminal window title.
 
-        IMPORTANT: This function will not set the title unless it can acquire self.terminal_lock to avoid writing
-                   to stderr while a command is running. Therefore it is best to acquire the lock before calling
-                   this function to guarantee the title changes and to avoid raising a RuntimeError.
+        NOTE: This function writes to stderr. Therefore if you call this during a command run by a pyscript,
+              the string which updates the title will appear in that command's CommandResult.stderr data.
 
         :param title: the new window title
         """
         if not vt100_support:
             return
 
-        # Sanity check that can't fail if self.terminal_lock was acquired before calling this function
-        if self.terminal_lock.acquire(blocking=False):
-            try:
-                sys.stderr.write(ansi.set_title_str(title))
-                sys.stderr.flush()
-            except AttributeError:
-                # Debugging in Pycharm has issues with setting terminal title
-                pass
-            finally:
-                self.terminal_lock.release()
-
-        else:
-            raise RuntimeError("another thread holds terminal_lock")
+        try:
+            sys.stderr.write(ansi.set_title_str(title))
+            sys.stderr.flush()
+        except AttributeError:
+            # Debugging in Pycharm has issues with setting terminal title
+            pass
 
     def enable_command(self, command: str) -> None:
         """

cmd2/rl_utils.py

@@ -8,7 +8,6 @@
 )
 from typing import (
     Union,
-    cast,
 )
 
 # Prefer statically linked gnureadline if available (for macOS compatibility due to issues with libedit)
@@ -197,7 +196,10 @@ def rl_get_prompt() -> str:  # pragma: no cover
     """Gets Readline's current prompt"""
     if rl_type == RlType.GNU:
         encoded_prompt = ctypes.c_char_p.in_dll(readline_lib, "rl_prompt").value
-        prompt = cast(bytes, encoded_prompt).decode(encoding='utf-8')
+        if encoded_prompt is None:
+            prompt = ''
+        else:
+            prompt = encoded_prompt.decode(encoding='utf-8')
 
     elif rl_type == RlType.PYREADLINE:
         prompt_data: Union[str, bytes] = readline.rl.prompt