default to "HEAD" revision

not every repo has a main or master, but they all have a HEAD
make sure that every Source has a rev

gitman/models/source.py

@@ -24,7 +24,7 @@ class Source:
     | --- | ------- | -------- | ------- |
     | `repo` | URL of the repository | Yes |
     | `name` | Directory for checkout | Yes | (inferred) |
-    | `rev` | SHA, tag, or branch to checkout | Yes | `"main"`|
+    | `rev` | SHA, tag, or branch to checkout | Yes | `"HEAD"`|
     | `type` | `"git"` or `"git-svn"` | No | `"git"` |
     | `params` | Additional arguments for `clone` | No | `null` |
     | `sparse_paths` | Controls partial checkout | No | `[]` |
@@ -66,7 +66,7 @@ class Source:
 
     repo: str = ""
     name: Optional[str] = None
-    rev: str = "main"
+    rev: str = "HEAD"
 
     type: str = "git"
     params: Optional[str] = None
@@ -84,6 +84,8 @@ def __post_init__(self):
         else:
             self.name = str(self.name)
         self.type = self.type or "git"
+        if not self.rev:
+            self.rev = "HEAD"
 
     def __repr__(self):
         return f"<source {self}>"

gitman/tests/test_models_source.py

@@ -20,7 +20,12 @@ def test_init_defaults(self):
 
         assert "http://example.com/foo/bar.git" == source.repo
         assert "bar" == source.name
-        assert "main" == source.rev
+        assert "HEAD" == source.rev
+
+    def test_init_invalid_rev_default_gets_corrected(self):
+        source = Source(type="git", repo="http://example.com/foo/bar.git", rev=None)
+
+        assert "HEAD" == source.rev
 
     def test_init_name_as_path(self, tmp_path):
         """Verify the name can be a path."""