Use expanduser() on Path arguments/options

Fixes fastapi#252

tests/test_main.py

@@ -0,0 +1,11 @@
+import pathlib
+
+from typer import main
+
+
+def test_param_path_convertor() -> None:
+    assert main.param_path_convertor(None) is None
+    assert main.param_path_convertor("/foo") == pathlib.Path("/foo")
+    # check that expanduser has been called.
+    # If we start to run tests on windows, we will probably need to update this
+    assert main.param_path_convertor("~/foo").to_posix().startswith("/")

typer/main.py

@@ -446,7 +446,7 @@ def get_command_from_info(command_info: CommandInfo) -> click.Command:
 
 def param_path_convertor(value: Optional[str] = None) -> Optional[Path]:
     if value is not None:
-        return Path(value)
+        return Path(value).expanduser()
     return None