Ability to suppress control-d exit behavior

[rolandwalker]

Description

Arguably the default should be changed since it can be confusing to new users. But exiting on control-d/EOF is also the default for eg bash.

Ringing the bell when no action can be taken is consistent with other control keys on the empty line.

Tests would be nice! But would require an alternate myclirc and simulated keypresses, which I don't know how to do.

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[scottnemes]

Verified new option controls the ctrl-d behavior as expected.

[github-actions]

Review summary

I focused on correctness/regressions, security, and missing tests. No security issues spotted. Two potential behavior/regression concerns and a test gap below.

Findings

1. Potential keybinding regression in non‑Emacs modes
   The new c-d binding is not gated by emacs_mode, so it will also fire in vi mode whenever the buffer is empty. That could override prompt_toolkit’s vi‑mode c-d behavior (if any) and may be unexpected for users running vi keybindings.
   Action: consider adding a mode filter (e.g., emacs_mode or vi_insert_mode depending on intended behavior), or explicitly document that this applies in all modes.
   File: mycli/key_bindings.py

2. Config typo silently disables exit
   Any value other than the literal 'exit' falls into the else branch and rings the bell, which effectively disables exit on Ctrl‑D without warning. A typo like control_d = exiit will be hard to diagnose.
   Action: treat unknown values as 'exit' (or log a warning) to avoid silent misconfiguration.
   File: mycli/key_bindings.py

Missing tests

1. Keybinding behavior for control_d
   Add tests that simulate Ctrl‑D on an empty buffer for both modes:
   • control_d = exit should trigger event.app.exit(exception=EOFError, ...)
   • control_d = none should not exit and should bell
     This can likely be done using prompt_toolkit’s testing utilities and a temporary config override.
     Files: mycli/key_bindings.py, test coverage (new test file)

If you want, I can sketch a minimal test harness for prompt_toolkit keybindings based on the existing test setup.