Support copying files to a directory

Since commit dbe0b1125f the `copy()` function no longer supports copying
files to a directory. The change in behaviour has lead to at least one
regression[1]. This restore the previous behaviour.

[1] https://github.com/getpelican/pelican/issues/3442

pelican/tests/test_utils.py

@@ -868,6 +868,18 @@ class TestCopy(unittest.TestCase):
         self._exist_dir("b0", "b1", "b2", "b3", "b")
         self._exist_file("b0", "b1", "b2", "b3", "b", "a.txt")
 
+    def test_copy_file_to_existing_dir(self):
+        self._create_dir("a")
+        self._create_file("a", "a.txt")
+        self._create_dir("b0", "b1")
+        utils.copy(
+            os.path.join(self.root_dir, "a", "a.txt"),
+            os.path.join(self.root_dir, "b0", "b1"),
+        )
+        self._exist_dir("b0")
+        self._exist_dir("b0", "b1")
+        self._exist_file("b0", "b1", "a.txt")
+
 
 class TestDateFormatter(unittest.TestCase):
     """Tests that the output of DateFormatter jinja filter is same as

pelican/utils.py

@@ -366,6 +366,9 @@ def copy(source: str, destination: str, ignores: Iterable[str] | None = None) ->
 
 def copy_file(source: str, destination: str) -> None:
     """Copy a file"""
+    if os.path.isdir(destination):
+        destination = os.path.join(destination, os.path.basename(source))
+
     try:
         shutil.copyfile(source, destination)
     except OSError as e: