Fixed #23759 -- Preserved all file extensions in Storage.get_available_name().

AUTHORS

@@ -21,6 +21,7 @@ answer newbie questions, and generally made Django that much better:
     Adam Johnson <https://github.com/adamchainz>
     Adam Malinowski <https://adammalinowski.co.uk/>
     Adam Vandenberg
+    Adam Zapletal <https://adamzap.com/>
     Ade Lee <alee@redhat.com>
     Adiyat Mubarak <adiyatmubarak@gmail.com>
     Adnan Umer <u.adnan@outlook.com>

django/core/files/storage/base.py

@@ -69,7 +69,8 @@ class Storage:
                 "Detected path traversal attempt in '%s'" % dir_name
             )
         validate_file_name(file_name)
-        file_root, file_ext = os.path.splitext(file_name)
+        file_ext = "".join(pathlib.PurePath(file_name).suffixes)
+        file_root = file_name.removesuffix(file_ext)
         # If the filename already exists, generate an alternative filename
         # until it doesn't exist.
         # Truncate original name if required, so the new filename does not

tests/file_storage/tests.py

@@ -769,18 +769,24 @@ class FileFieldStorageTests(TestCase):
 
     def test_duplicate_filename(self):
         # Multiple files with the same name get _(7 random chars) appended to them.
-        objs = [Storage() for i in range(2)]
-        for o in objs:
-            o.normal.save("multiple_files.txt", ContentFile("Same Content"))
-        try:
-            names = [o.normal.name for o in objs]
-            self.assertEqual(names[0], "tests/multiple_files.txt")
-            self.assertRegex(
-                names[1], "tests/multiple_files_%s.txt" % FILE_SUFFIX_REGEX
-            )
-        finally:
-            for o in objs:
-                o.delete()
+        tests = [
+            ("multiple_files", "txt"),
+            ("multiple_files_many_extensions", "tar.gz"),
+        ]
+        for filename, extension in tests:
+            with self.subTest(filename=filename):
+                objs = [Storage() for i in range(2)]
+                for o in objs:
+                    o.normal.save(f"{filename}.{extension}", ContentFile("Content"))
+                try:
+                    names = [o.normal.name for o in objs]
+                    self.assertEqual(names[0], f"tests/{filename}.{extension}")
+                    self.assertRegex(
+                        names[1], f"tests/{filename}_{FILE_SUFFIX_REGEX}.{extension}"
+                    )
+                finally:
+                    for o in objs:
+                        o.delete()
 
     def test_file_truncation(self):
         # Given the max_length is limited, when multiple files get uploaded