Merge pull request #194 from DanCardin/dc/optional-positional

fix: Optional positional arguments should not get a default value from their action.

Author: DanCardin

Diff for: CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## 0.26
 
+### 0.26.2
+
+- fix: Optional positional arguments should not get a default value from their action.
+
 ### 0.26.1
 
 - fix: Default formatting when value is None/Empty and formatter is supplied.

Diff for: pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "cappa"
-version = "0.26.1"
+version = "0.26.2"
 description = "Declarative CLI argument parser."
 
 urls = {repository = "https://github.com/dancardin/cappa"}

Diff for: src/cappa/argparse.py

@@ -229,7 +229,7 @@ def add_argument(
 
     is_positional = not names
 
-    num_args = backend_num_args(arg.num_args)
+    num_args = backend_num_args(arg.num_args, assert_type(arg.required, bool))
 
     kwargs: dict[str, typing.Any] = {
         "dest": dest_prefix + assert_type(arg.field_name, str),
@@ -295,12 +295,14 @@ def add_subcommands(
         )
 
 
-def backend_num_args(num_args: int | None) -> int | str | None:
+def backend_num_args(num_args: int | None, required: bool) -> int | str | None:
     if num_args is None or num_args == 1:
         return None
 
     if num_args == -1:
-        return "+"
+        if required:
+            return "+"
+        return "*"
 
     return num_args
 

Diff for: src/cappa/parser.py

@@ -597,13 +597,16 @@ def consume_arg(
                 arg=arg,
             )
     else:
-        missing_arg_requirement = (
-            # Positive fixed-arg amount
-            (orig_num_args > 0 and len(result) != orig_num_args)
-            # Unbounded but required arg
-            or (orig_num_args < 0 and arg.required and not result)
-        )
-        if missing_arg_requirement:
+        required_arg = arg.required
+        fixed_arg_mismatch = orig_num_args > 0 and len(result) != orig_num_args
+        unbounded_missing = orig_num_args < 0 and not result
+        if fixed_arg_mismatch or unbounded_missing:
+            option_requiring_values = option and requires_values
+            if not (required_arg or option_requiring_values or result):
+                # Lacking a consumed value for an optional positional arg should avoid
+                # hitting the argument's action, so as to apply it's default handling.
+                return
+
             quoted_result = [f"'{r}'" for r in result]
             names_str = arg.names_str("/")
 

Diff for: tests/arg/test_default_value_from.py

@@ -51,3 +51,50 @@ class Command:
 
     result = parse(Command, backend=backend)
     assert result == Command(0)
+
+
+def called():
+    return ["42"]
+
+
+@backends
+def test_positional_unbound_num_args(backend):
+    @dataclass
+    class Command:
+        positional: Annotated[
+            list[str],
+            cappa.Arg(
+                short=False,
+                long=False,
+                default=cappa.ValueFrom(called),
+            ),
+        ]
+
+    result = parse(Command, "7", backend=backend)
+    assert result == Command(["7"])
+
+    result = parse(Command, backend=backend)
+    assert result == Command(["42"])
+
+
+def two_tuple():
+    return ("42", "0")
+
+
+def test_optional_positional_2_tuple():
+    @dataclass
+    class Command:
+        positional: Annotated[
+            tuple[str, str],
+            cappa.Arg(
+                short=False,
+                long=False,
+                default=cappa.ValueFrom(two_tuple),
+            ),
+        ]
+
+    result = parse(Command, "7", "8")
+    assert result == Command(("7", "8"))
+
+    result = parse(Command)
+    assert result == Command(("42", "0"))