Add support for a custom completion key/key-combo in Prompt-toolkit using the completekey input

Author: tleonhardt

cmd2/cmd2.py

@@ -144,6 +144,7 @@
 from prompt_toolkit.formatted_text import ANSI
 from prompt_toolkit.history import InMemoryHistory
 from prompt_toolkit.input import DummyInput
+from prompt_toolkit.key_binding import KeyBindings
 from prompt_toolkit.output import DummyOutput
 from prompt_toolkit.patch_stdout import patch_stdout
 from prompt_toolkit.shortcuts import CompleteStyle, PromptSession, set_title
@@ -389,9 +390,19 @@ def __init__(
 
         # Key used for tab completion
         self.completekey = completekey
+        key_bindings = None
         if self.completekey != self.DEFAULT_COMPLETEKEY:
-            # TODO(T or K): Configure prompt_toolkit `KeyBindings` with the custom key for completion  # noqa: FIX002, TD003
-            pass
+            # Configure prompt_toolkit `KeyBindings` with the custom key for completion
+            key_bindings = KeyBindings()
+
+            @key_bindings.add(self.completekey)
+            def _(event: Any) -> None:
+                """Trigger completion."""
+                b = event.current_buffer
+                if b.complete_state:
+                    b.complete_next()
+                else:
+                    b.start_completion(select_first=False)
 
         # Attributes which should NOT be dynamically settable via the set command at runtime
         self.default_to_shell = False  # Attempt to run unrecognized commands as shell commands
@@ -448,6 +459,7 @@ def __init__(
                 complete_style=CompleteStyle.COLUMN,
                 complete_in_thread=True,
                 complete_while_typing=False,
+                key_bindings=key_bindings,
             )
         except (NoConsoleScreenBufferError, AttributeError, ValueError):
             # Fallback to dummy input/output if PromptSession initialization fails.
@@ -461,6 +473,7 @@ def __init__(
                 complete_style=CompleteStyle.COLUMN,
                 complete_in_thread=True,
                 complete_while_typing=False,
+                key_bindings=key_bindings,
             )
 
         # Commands to exclude from the history command

tests/test_custom_key_binding.py

@@ -0,0 +1,22 @@
+from prompt_toolkit.keys import Keys
+
+import cmd2
+
+
+def test_custom_completekey_ctrl_k():
+    # Test setting a custom completekey to <CTRL> + K
+    # In prompt_toolkit, this is 'c-k'
+    app = cmd2.Cmd(completekey='c-k')
+
+    assert app.completekey == 'c-k'
+    assert app.session.key_bindings is not None
+
+    # Check that we have a binding for c-k (Keys.ControlK)
+    found = False
+    for binding in app.session.key_bindings.bindings:
+        # binding.keys is a tuple of keys
+        if binding.keys == (Keys.ControlK,):
+            found = True
+            break
+
+    assert found, "Could not find binding for 'c-k' (Keys.ControlK) in session key bindings"