Allow any file extension for README file (#5357)

Co-authored-by: Bjorn Neergaard <bjorn@neersighted.com>

docs/cli.md

@@ -103,7 +103,9 @@ my-package
 
 * `--name`: Set the resulting package name.
 * `--src`: Use the src layout for the project.
-* `--readme`: Specify the readme file format. One of `md` (default) or `rst`.
+* `--readme`: Specify the readme file extension. Default is `md`. If you intend to publish to PyPI
+  keep the [recommendations for a PyPI-friendly README](https://packaging.python.org/en/latest/guides/making-a-pypi-friendly-readme/)
+  in mind.
 
 
 ## init

src/poetry/layouts/layout.py

@@ -41,8 +41,6 @@
 
 
 class Layout:
-    ACCEPTED_README_FORMATS = {"md", "rst"}
-
     def __init__(
         self,
         project: str,
@@ -64,12 +62,6 @@ def __init__(
         self._description = description
 
         self._readme_format = readme_format.lower()
-        if self._readme_format not in self.ACCEPTED_README_FORMATS:
-            accepted_readme_formats = ", ".join(self.ACCEPTED_README_FORMATS)
-            raise ValueError(
-                f"Invalid readme format '{readme_format}', use one of"
-                f" {accepted_readme_formats}."
-            )
 
         self._license = license
         self._python = python

tests/console/commands/test_new.py

@@ -157,7 +157,7 @@ def test_command_new(
     verify_project_directory(path, package_name, package_path, include_from)
 
 
-@pytest.mark.parametrize(("fmt",), [(None,), ("md",), ("rst",)])
+@pytest.mark.parametrize(("fmt",), [(None,), ("md",), ("rst",), ("adoc",), ("creole",)])
 def test_command_new_with_readme(fmt: str | None, tester: CommandTester, tmp_dir: str):
     package = "package"
     path = Path(tmp_dir) / package