Fix traceback when not passing file to -o option (#698)

If precli-init is run without an argument for the -o, it will fail with
a traceback due to the argparse.FileType not allowing a default of a str
for a file name.

This change does the logic of detecting and opening files manually on
its own. It will present an error if the file already exists to prevent
overwriting. Except in the case where the file is pyproject.toml and the
settings will be appended to it.

Signed-off-by: Eric Brown <eric.brown@securesauce.dev>

precli/cli/init.py

@@ -25,12 +25,20 @@ def setup_arg_parser() -> Namespace:
         "--output",
         dest="output",
         action="store",
-        type=argparse.FileType("x", encoding="utf-8"),
+        type=str,
         default=".precli.toml",
-        help="output the config to given file",
+        help="output the config to given file (default: .precli.toml)",
     )
     args = parser.parse_args()
 
+    # Prevent overwriting output files except appending to pyproject.toml
+    path = pathlib.Path(args.output)
+    if path.exists() and path.name != "pyproject.toml":
+        parser.error(
+            f"argument -o/--output: can't open '{args.output}': [Errno 17] "
+            f"File exists: '{args.output}'"
+        )
+
     return args
 
 

tests/unit/cli/test_init.py

@@ -12,15 +12,6 @@
 
 class TestInit:
     @classmethod
-    def test_main_invalid_output(self, monkeypatch):
-        monkeypatch.setattr(
-            "sys.argv",
-            ["precli-init", "-o", "../does/not/exist"],
-        )
-        with pytest.raises(SystemExit) as excinfo:
-            init.main()
-        assert excinfo.value.code == 2
-
     def test_main_output_already_exists(self, monkeypatch, capsys):
         temp_dir = tempfile.mkdtemp()
         output_path = os.path.join(temp_dir, "output.txt")