🐛 Fix list convertor with an empty list default factory (#1350)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: svlandeg

tests/test_others.py

@@ -14,6 +14,7 @@
 from typer.main import solve_typer_info_defaults, solve_typer_info_help
 from typer.models import ParameterInfo, TyperInfo
 from typer.testing import CliRunner
+from typing_extensions import Annotated
 
 from .utils import requires_completion_permission
 
@@ -170,6 +171,22 @@ def main(
     assert "Hello World" in result.stdout
 
 
+def test_empty_list_default_generator():
+    def empty_list() -> typing.List[str]:
+        return []
+
+    app = typer.Typer()
+
+    @app.command()
+    def main(
+        names: Annotated[typing.List[str], typer.Option(default_factory=empty_list)],
+    ):
+        print(names)
+
+    result = runner.invoke(app)
+    assert "[]" in result.output
+
+
 def test_completion_argument():
     file_path = Path(__file__).parent / "assets/completion_argument.py"
     result = subprocess.run(

typer/main.py

@@ -629,8 +629,8 @@ def generate_list_convertor(
     convertor: Optional[Callable[[Any], Any]], default_value: Optional[Any]
 ) -> Callable[[Optional[Sequence[Any]]], Optional[List[Any]]]:
     def internal_convertor(value: Optional[Sequence[Any]]) -> Optional[List[Any]]:
-        if value is None or len(value) == 0:
-            return default_value
+        if (value is None) or (default_value is None and len(value) == 0):
+            return None
         return [convertor(v) if convertor else v for v in value]
 
     return internal_convertor