Fix #2164

Author: kdeldycke

src/click/core.py

@@ -3165,10 +3165,6 @@ def __init__(
 
         super().__init__(param_decls, required=required, **attrs)
 
-        if __debug__:
-            if self.default not in (None, UNSET) and self.nargs == -1:
-                raise TypeError("'default' is not supported for nargs=-1.")
-
     @property
     def human_readable_name(self) -> str:
         if self.metavar is not None:

src/click/parser.py

@@ -204,8 +204,8 @@ def process(
                     )
                 )
 
-        # Unset empty tuple so that a value from the environment may be tried.
-        if self.nargs == -1 and self.obj.envvar is not None and value == ():
+        # We failed to collect any argument value so we consider the argument as unset.
+        if value == ():
             value = UNSET
 
         state.opts[self.dest] = value  # type: ignore

tests/test_arguments.py

@@ -20,15 +20,6 @@ def copy(src, dst):
     assert result.output.splitlines() == ["src=foo.txt|bar.txt", "dst=dir"]
 
 
-def test_argument_unbounded_nargs_cant_have_default(runner):
-    with pytest.raises(TypeError, match="nargs=-1"):
-
-        @click.command()
-        @click.argument("src", nargs=-1, default=["42"])
-        def copy(src):
-            pass
-
-
 def test_nargs_tup(runner):
     @click.command()
     @click.argument("name", nargs=1)
@@ -379,26 +370,31 @@ def cmd(a, b, c):
 
 
 @pytest.mark.parametrize(
-    ("args", "default", "expected"),
+    ("argument_params", "args", "expected"),
     [
         # Any iterable with the same number of arguments as nargs is valid.
-        [[], (1, 2), (1, 2)],
-        [[], (1.1, 2.2), (1, 2)],
-        [[], ("1", "2"), (1, 2)],
-        [[], (None, None), (None, None)],
-        [[], [1, 2], (1, 2)],
-        [[], {1, 2}, (1, 2)],
-        [[], frozenset([1, 2]), (1, 2)],
-        [[], {1: "a", 2: "b"}, (1, 2)],
+        [{"nargs": 2, "default": (1, 2)}, [], (1, 2)],
+        [{"nargs": 2, "default": (1.1, 2.2)}, [], (1, 2)],
+        [{"nargs": 2, "default": ("1", "2")}, [], (1, 2)],
+        [{"nargs": 2, "default": (None, None)}, [], (None, None)],
+        [{"nargs": 2, "default": [1, 2]}, [], (1, 2)],
+        [{"nargs": 2, "default": {1, 2}}, [], (1, 2)],
+        [{"nargs": 2, "default": frozenset([1, 2])}, [], (1, 2)],
+        [{"nargs": 2, "default": {1: "a", 2: "b"}}, [], (1, 2)],
         # Empty iterable is valid if default is None.
-        [[], None, None],
+        [{"nargs": 2, "default": None}, [], None],
         # Arguments overrides the default.
-        [["3", "4"], (1, 2), (3, 4)],
+        [{"nargs": 2, "default": (1, 2)}, ["3", "4"], (3, 4)],
+        # Unbounded arguments are allowed to have a default.
+        # See: https://github.com/pallets/click/issues/2164
+        [{"nargs": -1, "default": [42]}, [], (42,)],
+        [{"nargs": -1, "default": None}, [], ()],
+        [{"nargs": -1, "default": {1, 2, 3, 4, 5}}, [], (1, 2, 3, 4, 5)],
     ],
 )
-def test_good_defaults_for_nargs(runner, args, default, expected):
+def test_good_defaults_for_nargs(runner, argument_params, args, expected):
     @click.command()
-    @click.argument("a", nargs=2, type=int, default=default)
+    @click.argument("a", type=int, **argument_params)
     def cmd(a):
         click.echo(repr(a), nl=False)