Fix utils.copy_tree() to create dst if it doesn't exist (#1231)

## Proposed Changes

Kapitan's `utils.copy_tree()` calls `shutil.copytree()` which will
create the destination directory if it doesn't exist yet. However,
currently, `utils.copy_tree()` doesn't support this case and will raise
a `SafeCopyError` when the destination directory doesn't exist.

This PR adjusts the implementation to only raise a `SafeCopyError` when
the destination exists and isn't a directory and will let
`shutil.copytree()` create the destination if the destination doesn't
exist at all.

## Docs and Tests

* [x] Tests added
* [x] Updated documentation

kapitan/utils.py

@@ -631,14 +631,17 @@ def safe_copy_tree(src, dst):
 def copy_tree(src: str, dst: str) -> list:
     """Recursively copy a given directory from `src` to `dst`.
 
+    If `dst` or a parent of `dst` doesn't exist, the missing directories are created.
+
     Returns a list of the copied files.
     """
     if not os.path.isdir(src):
         raise SafeCopyError(f"Cannot copy tree {src}: not a directory")
 
-    if not os.path.isdir(dst):
-        raise SafeCopyError(f"Cannot copy tree {dst}: not a directory")
+    if os.path.exists(dst) and not os.path.isdir(dst):
+        raise SafeCopyError(f"Cannot copy tree to {dst}: destination exists but not a directory")
 
+    # this will generate an empty set if `dst` doesn't exist
     before = set(glob.iglob(f"{dst}/*", recursive=True))
     shutil.copytree(src, dst, dirs_exist_ok=True)
     after = set(glob.iglob(f"{dst}/*", recursive=True))

tests/test_utils.py

@@ -41,5 +41,21 @@ def test_validate_copy_dir(self):
         with self.assertRaises(SafeCopyError):
             copy_tree("non_existent_dir", self.temp_dir)
 
+        dst = os.path.join(self.temp_dir, "test")
+        with open(dst, "w", encoding="utf-8") as f:
+            f.write("Hello\n")
+        with self.assertRaises(SafeCopyError):
+            copy_tree(TEST_KUBERNETES_PATH, dst)
+
+    def test_copy_dir_missing_dst(self):
+        dst = os.path.join(self.temp_dir, "subdir")
+        original = set(glob.iglob(f"{TEST_KUBERNETES_PATH}/*", recursive=True))
+        copied = copy_tree(TEST_KUBERNETES_PATH, dst)
+        self.assertEqual(len(copied), len(original))
+
+        original_hash = directory_hash(TEST_KUBERNETES_PATH)
+        copied_hash = directory_hash(dst)
+        self.assertEqual(copied_hash, original_hash)
+
     def tearDown(self):
         shutil.rmtree(self.temp_dir)