[DRAFT] Migrate from using readline to prompt-toolkit

.github/CODEOWNERS

@@ -38,9 +38,9 @@ cmd2/exceptions.py         @kmvanbrunt @anselor
 cmd2/history.py            @tleonhardt
 cmd2/parsing.py            @kmvanbrunt
 cmd2/plugin.py             @anselor
+cmd2/pt_utils.py           @kmvanbrunt @tleonhardt
 cmd2/py_bridge.py          @kmvanbrunt
 cmd2/rich_utils.py         @kmvanbrunt
-cmd2/rl_utils.py           @kmvanbrunt
 cmd2/string_utils.py       @kmvanbrunt
 cmd2/styles.py             @tleonhardt @kmvanbrunt
 cmd2/terminal_utils.py     @kmvanbrunt

.github/CONTRIBUTING.md

@@ -61,15 +61,13 @@ Nearly all project configuration, including for dependencies and quality tools i
 
 See the `dependencies` list under the `[project]` heading in [pyproject.toml](../pyproject.toml).
 
-| Prerequisite                                               | Minimum Version | Purpose                                                |
-| ---------------------------------------------------------- | --------------- | ------------------------------------------------------ |
-| [python](https://www.python.org/downloads/)                | `3.10`          | Python programming language                            |
-| [pyperclip](https://github.com/asweigart/pyperclip)        | `1.8`           | Cross-platform clipboard functions                     |
-| [rich](https://github.com/Textualize/rich)                 | `14.1.0`        | Add rich text and beautiful formatting in the terminal |
-| [rich-argparse](https://github.com/hamdanal/rich-argparse) | `1.7.1`         | A rich-enabled help formatter for argparse             |
-
-> `macOS` and `Windows` each have an extra dependency to ensure they have a viable alternative to
-> [readline](https://tiswww.case.edu/php/chet/readline/rltop.html) available.
+| Prerequisite                                                              | Minimum Version | Purpose                                                |
+| ------------------------------------------------------------------------- | --------------- | ------------------------------------------------------ |
+| [prompt-toolkit](https://github.com/prompt-toolkit/python-prompt-toolkit) | `3.0.52`        | Replacement for GNU `readline` that is cross-platform  |
+| [python](https://www.python.org/downloads/)                               | `3.10`          | Python programming language                            |
+| [pyperclip](https://github.com/asweigart/pyperclip)                       | `1.8`           | Cross-platform clipboard functions                     |
+| [rich](https://github.com/Textualize/rich)                                | `14.1.0`        | Add rich text and beautiful formatting in the terminal |
+| [rich-argparse](https://github.com/hamdanal/rich-argparse)                | `1.7.1`         | A rich-enabled help formatter for argparse             |
 
 > Python 3.10 depends on [backports.strenum](https://github.com/clbarnes/backports.strenum) to use
 > the `enum.StrEnum` class introduced in Python 3.11.

CHANGELOG.md

@@ -1,3 +1,27 @@
+## 4.0.0 (TBD 2026)
+
+### Summary
+
+`cmd2` now has a dependency on
+[prompt-toolkit](https://github.com/prompt-toolkit/python-prompt-toolkit) which serves as a
+pure-Python cross-platform replacement for
+[GNU Readline](https://tiswww.case.edu/php/chet/readline/rltop.html). Previously, `cmd2` had used
+different `readline` dependencies on each Operating System (OS) which was at times a very
+frustrating developer and user experience due to small inconsistencies in these different readline
+libraries. Now we have consistent cross-platform support for tab-completion, user terminal input,
+and history. Additionally, this opens up some cool advanced features such as support for syntax
+highlighting of user input while typing, auto-suggestions similar to those provided by the fish
+shell, and the option for a persistent bottom bar that can display realtime status updates.
+
+### Details
+
+- Breaking Changes
+    - Removed all use of `readline` built-in module and underlying platform libraries
+    - Deleted `cmd2.rl_utils` module which dealt with importing the proper `readline` module for
+      each platform and provided utility functions related to `readline`
+    - Added a dependency on `prompt-toolkit` and a new `cmd2.pt_utils` module with supporting
+      utilities
+
 ## 3.1.0 (December 25, 2025)
 
 - Potentially Breaking Changes

Makefile

@@ -77,7 +77,8 @@ publish: validate-tag build ## Publish a release to PyPI, uses token from ~/.pyp
 BUILD_DIRS = build dist *.egg-info
 DOC_DIRS = build
 MYPY_DIRS = .mypy_cache dmypy.json dmypy.sock
-TEST_DIRS = .cache .coverage .pytest_cache htmlcov
+TEST_DIRS = .cache .pytest_cache htmlcov
+TEST_FILES = .coverage coverage.xml
 
 .PHONY: clean-build
 clean-build: ## Clean build artifacts
@@ -108,6 +109,7 @@ clean-ruff: ## Clean ruff artifacts
 clean-test: ## Clean test artifacts
 	@echo "🚀 Removing test artifacts"
 	@uv run python -c "import shutil; import os; [shutil.rmtree(d, ignore_errors=True) for d in '$(TEST_DIRS)'.split() if os.path.isdir(d)]"
+	@uv run python -c "from pathlib import Path; [Path(f).unlink(missing_ok=True) for f in '$(TEST_FILES)'.split()]"
 
 .PHONY: clean
 clean: clean-build clean-docs clean-mypy clean-pycache clean-ruff clean-test ## Clean all artifacts