Support python -m dargs from source checkouts

dargs/cli.py

@@ -3,9 +3,29 @@
 import argparse
 import json
 import sys
+from importlib import import_module
 from typing import IO, Any
 
-from dargs._version import __version__
+try:
+    from dargs._version import __version__
+except ModuleNotFoundError as exc:
+    if exc.name != "dargs._version":
+        raise
+    try:
+        get_version = getattr(import_module("setuptools_scm"), "get_version")
+    except ModuleNotFoundError as scm_exc:
+        if scm_exc.name != "setuptools_scm":
+            raise
+        # Source archives may have neither the generated module nor build tools.
+        # The CLI should remain usable even when an exact version is unavailable.
+        __version__ = "0+unknown"
+    else:
+        __version__ = get_version(
+            root="..",
+            relative_to=__file__,
+            fallback_version="0+unknown",
+        )
+
 from dargs.check import check
 
 

tests/test_cli.py

@@ -9,6 +9,16 @@
 
 
 class TestCli(unittest.TestCase):
+    def test_version_with_python_module(self) -> None:
+        """The source checkout exposes a version without generated build files."""
+        result = subprocess.run(
+            [sys.executable, "-m", "dargs", "--version"],
+            capture_output=True,
+            text=True,
+            check=True,
+        )
+        self.assertTrue(result.stdout.strip())
+
     def test_check(self) -> None:
         subprocess.check_call(
             [