fix: avoids build crash from setup.cfg generating a version file deepcharles#353

Author: wangkechun

setup.py

@@ -1,4 +1,6 @@
+import os
 from setuptools import Extension, setup
+from setuptools_scm import get_version
 
 ext_modules = [
     Extension(
@@ -19,10 +21,19 @@
     ),
 ]
 
-
 if __name__ == "__main__":
     from Cython.Build import cythonize
 
+    version_file = os.path.join("src", "ruptures", "version.py")
+    if not os.path.exists(version_file):
+        version = get_version(root=".", relative_to=__file__)
+        if not version:
+            raise RuntimeError(
+                "Version could not be determined. Ensure you have a valid git tag."
+            )
+        with open(version_file, "w") as f:
+            f.write(f'__version__ = version = "{version}"\n')
+
     setup(
         ext_modules=cythonize(ext_modules, language_level="3"),
     )