ignore unexported git archivals

fixes #742
fixes #745

src/setuptools_scm/git.py

@@ -295,10 +295,13 @@ def archival_to_version(
         return meta(versions[0], config=config)
     else:
         node = data.get("node")
-        if node is not None:
-            return meta("0.0", node=node, config=config)
-        else:
+        if node is None:
             return None
+        elif "$FORMAT" in node.upper():
+            warnings.warn("unexported git archival found")
+            return None
+        else:
+            return meta("0.0", node=node, config=config)
 
 
 def parse_archival(

testing/test_git.py

@@ -24,6 +24,7 @@
 from setuptools_scm import NonNormalizedVersion
 from setuptools_scm.file_finder_git import git_find_files
 from setuptools_scm.git import archival_to_version
+from setuptools_scm.utils import data_from_mime
 from setuptools_scm.utils import do
 from setuptools_scm.utils import has_command
 
@@ -543,3 +544,14 @@ def test_git_archival_node_missing_no_version() -> None:
     config = Configuration()
     version = archival_to_version({}, config=config)
     assert version is None
+
+
+def test_git_archhival_from_unfiltered() -> None:
+    config = Configuration()
+
+    import setuptools_scm
+
+    data = data_from_mime(Path(setuptools_scm.__file__).parent / ".git_archival.txt")
+    with pytest.warns(UserWarning, match="unexported git archival found"):
+        version = archival_to_version(data, config=config)
+    assert version is None