Now that cmd2 3.0.0 is out, it's time to start discussing what we would like to see in the 4.0.0 release for cmd2.

Features @kmvanbrunt and I have discussed for 4.x include:

• Remove explicit dependency on Python's built-in cmd module, but retain backwards compatibility (PR Remove dependency on Python's built-in cmd module #1539)
• Replace dependency on twine for publishing PyPI package with one on uv publish (Use uv for publishing to PyPI instead of twine #1548)
• Replace use of invoke with use of make, primarily used for cleanup at this point (Add clean target to Makefile that runs what is in invoke clean #1549)
• Migrate documentation to Zensical which is essentially MkDocs 2.0, but implemented in Rust and much faster (PR Migrate documentation to use Zensical instead of MkDocs #1557)
• Remove dependency on Python's built-in readline module and replace it with a dependency on prompt-toolkit which is a pure Python replacement for GNU Readline (PR Migrate from using readline to prompt-toolkit #1553)
  • Support adding a bottom toolbar to display real-time status via prompt-toolkit (PR Migrate from using readline to prompt-toolkit #1553)
  • Add prompt-toolkit syntax highlighting of text entered by users, at least for command names (PR Migrate from using readline to prompt-toolkit #1553)
  • Add support for prompt-toolkit Input Validation - I looked into this and honestly if we add support for more advanced input validation, I would prefer to add a dependency on pydantic and go that route. But that is more than I want to bite off for the 4.0 release of cmd2.
  • Add auto-suggestions using prompt-toolkit similar to fish-shell where it will show a recommended completion grayed-out per user request in Add auto suggestion feature #1545 (PR Migrate from using readline to prompt-toolkit #1553)
• Handle prompt-toolkit completion edge cases related to adding quotes (PR Refactor completion API #1575)
• Consider implementing syntax that is essentially compatible with Typer for defining command arguments based on type hints. A user documented how to do this in Discussion A plugin for Typer command define within cmd2 #1530.
  • For this I envision something like a @cmd2.typer decorator that will auto-generate an argparse.ArgumentParser based on argument annotations
  • We won't be tackling this in the 4.0.0 release unless someone else wants to do the work
• Remove the transcript testing feature set (PR Remove the Transcript Testing feature #1583)
• Investigate migrating type-checking from mypy to ty now that ty is in beta
  • Will revisit this in the future after releasing 4.0.0. This isn't a backwards incompatible change for anyone and I'd like to wait for this library to mature a little more before migrating to it
• Replace restrictive type hints (e.g. list) with broader ones like Sequence or Iterable (PR Use more generic types where possible for input parameters #1584)
• Ensure examples all work
• Change async alert methods to rely on a queue (PR Refactored async alerts. #1586)
• Remove the default_to_shell flag since it can result in unintended execution which can be dangerous (PR Removed default_to_shell. #1590)
• Restore concatenating all lines of a multi-line command into one for the up-arrow history (PR Switch to using prompt-toolkit's multiline filtering. #1589)
• Fix Cmd2Lexer coloring of command names used on continued lines in multiline commands (PR Fixed multiline command highlighting in Cmd2Lexer #1591)
• Ensure documentation and CHANGELOG are fully up to date

Moving to prompt-toolkit and no longer depending on cmd will be a large paradigm shift for cmd2. But this will open doors for easier and more consistent cross-platform support as well as being able to provide some more advanced features that we cannot now.