Allow Custom Version Scheme Outside setup.py (resolves #781)

README.rst

@@ -628,6 +628,25 @@ The callable must return the configuration.
     )
 
 
+Customizing Version Scheme with pyproject.toml
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To support custom version schemes in pyproject.toml, you may specify your own function as an entrypoint for getting the version.
+
+.. code:: toml
+
+    # pyproject.toml
+    [tool.setuptools_scm]
+    version_scheme = "myproject.my_file:myversion_func"
+
+.. code:: python
+
+    # myproject/my_file
+    def myversion_func(version: ScmVersion):
+        from setuptools_scm.version import guess_next_version
+        return version.format_next_version(guess_next_version, '{guessed}b{distance}')
+
+
 Note on testing non-installed versions
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

src/setuptools_scm/_entrypoints.py

@@ -46,9 +46,11 @@ def _version_from_entrypoints(
 
 try:
     from importlib.metadata import entry_points  # type: ignore
+    from importlib.metadata import EntryPoint
 except ImportError:
     try:
         from importlib_metadata import entry_points
+        from importlib_metadata import EntryPoint
     except ImportError:
         from collections import defaultdict
 
@@ -59,6 +61,10 @@ def entry_points() -> dict[str, list[_t.EntrypointProtocol]]:
             )
             return defaultdict(list)
 
+        class EntryPoint:  # type: ignore
+            def __init__(self, *args: Any, **kwargs: Any):
+                pass  # entry_points() already provides the warning
+
 
 def iter_entry_points(
     group: str, name: str | None = None
@@ -83,6 +89,13 @@ def _get_ep(group: str, name: str) -> Any | None:
         return None
 
 
+def _get_from_object_reference_str(path: str) -> Any | None:
+    try:
+        return EntryPoint(path, path, None).load()
+    except (AttributeError, ModuleNotFoundError):
+        return None
+
+
 def _iter_version_schemes(
     entrypoint: str,
     scheme_value: _t.VERSION_SCHEMES,
@@ -93,7 +106,8 @@ def _iter_version_schemes(
     if isinstance(scheme_value, str):
         scheme_value = cast(
             "_t.VERSION_SCHEMES",
-            _get_ep(entrypoint, scheme_value),
+            _get_ep(entrypoint, scheme_value)
+            or _get_from_object_reference_str(scheme_value),
         )
 
     if isinstance(scheme_value, (list, tuple)):

testing/test_version.py

@@ -214,6 +214,16 @@ def test_format_version_schemes() -> None:
     )
 
 
+def test_custom_version_schemes() -> None:
+    version = meta("1.0", config=c)
+    custom_computed = format_version(
+        version,
+        local_scheme="no-local-version",
+        version_scheme="setuptools_scm.version:no_guess_dev_version",
+    )
+    assert custom_computed == no_guess_dev_version(version)
+
+
 def date_to_str(
     date_: date | None = None,
     days_offset: int = 0,