Allow simple container literals as default values (#358)

Resolves #357

CHANGELOG.md

@@ -11,6 +11,8 @@ New error codes:
   it now applies everywhere.
 
 Other changes:
+* Y011/Y014/Y015: Simple container literals (`list`, `dict`, `tuple` and `set`
+  literals) are now allowed as default values.
 * Y052 is now emitted more consistently.
 * Some things that used to result in Y011, Y014 or Y015 being emitted
   now result in Y053 or Y054 being emitted.

README.md

@@ -44,7 +44,7 @@ currently emitted:
 | Y008 | Unrecognized platform in a `sys.platform` check. To prevent you from typos, we warn if you use a platform name outside a small set of known platforms (e.g. `"linux"` and `"win32"`).
 | Y009 | Empty class or function body should contain `...`, not `pass`. This is just a stylistic choice, but it's the one typeshed made.
 | Y010 | Function body must contain only `...`. Stub files should not contain code, so function bodies should be empty.
-| Y011 | Only simple default values (`int`, `float`, `complex`, `bytes`, `str`, `bool`, `None` or `...`) are allowed for typed function arguments. Type checkers ignore the default value, so the default value is not useful information for type-checking, but it may be useful information for other users of stubs such as IDEs. If you're writing a stub for a function that has a more complex default value, use `...` instead of trying to reproduce the runtime default exactly in the stub. Also use `...` for very long numbers, very long strings, very long bytes, or defaults that vary according to the machine Python is being run on.
+| Y011 | Only simple default values (`int`, `float`, `complex`, `bytes`, `str`, `bool`, `None`, `...`, or simple container literals) are allowed for typed function arguments. Type checkers ignore the default value, so the default value is not useful information for type-checking, but it may be useful information for other users of stubs such as IDEs. If you're writing a stub for a function that has a more complex default value, use `...` instead of trying to reproduce the runtime default exactly in the stub. Also use `...` for very long numbers, very long strings, very long bytes, or defaults that vary according to the machine Python is being run on.
 | Y012 | Class body must not contain `pass`.
 | Y013 | Non-empty class body must not contain `...`.
 | Y014 | Only simple default values are allowed for any function arguments. A stronger version of Y011 that includes arguments without type annotations.

pyi.py

@@ -719,13 +719,42 @@ def _analyse_union(members: Sequence[ast.expr]) -> UnionAnalysis:
 )
 
 
-def _is_valid_default_value_with_annotation(node: ast.expr) -> bool:
+def _is_valid_default_value_with_annotation(
+    node: ast.expr, allow_containers=True
+) -> bool:
     """Is `node` valid as a default value for a function or method parameter in a stub?
 
     Note that this function is *also* used to determine
     the validity of default values for ast.AnnAssign nodes.
     (E.g. `foo: int = 5` is OK, but `foo: TypeVar = TypeVar("foo")` is not.)
     """
+    # lists, tuples, sets
+    if isinstance(node, (ast.List, ast.Tuple, ast.Set)):
+        return (
+            allow_containers
+            and len(node.elts) <= 10
+            and all(
+                _is_valid_default_value_with_annotation(elt, allow_containers=False)
+                for elt in node.elts
+            )
+        )
+
+    # dicts
+    if isinstance(node, ast.Dict):
+        return (
+            allow_containers
+            and len(node.keys) <= 10
+            and all(
+                (
+                    subnode is not None
+                    and _is_valid_default_value_with_annotation(
+                        subnode, allow_containers=False
+                    )
+                )
+                for subnode in chain(node.keys, node.values)
+            )
+        )
+
     # `...`, bools, None, str, bytes,
     # positive ints, positive floats, positive complex numbers with no real part
     if isinstance(node, (ast.Ellipsis, ast.NameConstant, ast.Str, ast.Bytes, ast.Num)):

tests/attribute_annotations.pyi

@@ -32,6 +32,15 @@ field9 = None  # Y026 Use typing_extensions.TypeAlias for type aliases, e.g. "fi
 Field95: TypeAlias = None
 Field96: TypeAlias = int | None
 Field97: TypeAlias = None | typing.SupportsInt | builtins.str | float | bool
+field19 = [1, 2, 3]  # Y052 Need type annotation for "field19"
+field191: list[int] = [1, 2, 3]
+field20 = (1, 2, 3)  # Y052 Need type annotation for "field20"
+field201: tuple[int, ...] = (1, 2, 3)
+field21 = {1, 2, 3}  # Y052 Need type annotation for "field21"
+field211: set[int] = {1, 2, 3}
+field212 = {"foo": "bar"}  # Y052 Need type annotation for "field212"
+field213: dict[str, str] = {"foo": "bar"}
+field22: Final = {"foo": 5}
 
 # Tests for Final
 field11: Final = 1
@@ -47,10 +56,16 @@ field182: Final = os.pathsep
 field183: Final = None
 
 # We *should* emit Y015 for more complex default values
-field19 = [1, 2, 3]  # Y015 Only simple default values are allowed for assignments
-field20 = (1, 2, 3)  # Y015 Only simple default values are allowed for assignments
-field21 = {1, 2, 3}  # Y015 Only simple default values are allowed for assignments
-field22: Final = {"foo": 5}  # Y015 Only simple default values are allowed for assignments
+field221: list[int] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]  # Y015 Only simple default values are allowed for assignments
+field222: list[int] = [100000000000000000000000000000]  # Y054 Numeric literals with a string representation >10 characters long are not permitted
+field223: list[int] = [*range(10)]  # Y015 Only simple default values are allowed for assignments
+field224: list[int] = list(range(10))  # Y015 Only simple default values are allowed for assignments
+field225: list[object] = [{}, 1, 2]  # Y015 Only simple default values are allowed for assignments
+field226: tuple[str | tuple[str, ...], ...] = ("foo", ("foo", "bar"))  # Y015 Only simple default values are allowed for assignments
+field227: dict[str, object] = {"foo": {"foo": "bar"}}  # Y015 Only simple default values are allowed for assignments
+field228: dict[str, list[object]] = {"foo": []}  # Y015 Only simple default values are allowed for assignments
+# When parsed, this case results in `None` being placed in the `.keys` list for the `ast.Dict` node
+field229: dict[int, int] = {1: 2, **{3: 4}}  # Y015 Only simple default values are allowed for assignments
 field23 = "foo" + "bar"  # Y015 Only simple default values are allowed for assignments
 field24 = b"foo" + b"bar"  # Y015 Only simple default values are allowed for assignments
 field25 = 5 * 5  # Y015 Only simple default values are allowed for assignments
@@ -91,10 +106,13 @@ class Foo:
     else:
         field19 = "w"  # Y052 Need type annotation for "field19"
 
-    field20 = [1, 2, 3]  # Y015 Only simple default values are allowed for assignments
-    field21 = (1, 2, 3)  # Y015 Only simple default values are allowed for assignments
-    field22 = {1, 2, 3}  # Y015 Only simple default values are allowed for assignments
-    field23: Final = {"foo": 5}  # Y015 Only simple default values are allowed for assignments
+    field20 = [1, 2, 3]  # Y052 Need type annotation for "field20"
+    field201: list[int] = [1, 2, 3]
+    field21 = (1, 2, 3)  # Y052 Need type annotation for "field21"
+    field211: tuple[int, ...] = (1, 2, 3)
+    field22 = {1, 2, 3}  # Y052 Need type annotation for "field22"
+    field221: set[int] = {1, 2, 3}
+    field23: Final = {"foo": 5}
     field24 = "foo" + "bar"  # Y015 Only simple default values are allowed for assignments
     field25 = b"foo" + b"bar"  # Y015 Only simple default values are allowed for assignments
     field26 = 5 * 5  # Y015 Only simple default values are allowed for assignments

tests/defaults.pyi

@@ -35,9 +35,16 @@ def f901(x, y: str = os.pathsep) -> None: ...  # Y011 Only simple default values
 def f10(x, y: str = ..., *args: "int") -> None: ...  # Y020 Quoted annotations should never be used in stubs
 def f11(*, x: str = "x") -> None: ...
 def f12(*, x: str = ..., **kwargs: "int") -> None: ...  # Y020 Quoted annotations should never be used in stubs
-def f13(x: list[str] = ["foo", "bar", "baz"]) -> None: ...  # Y011 Only simple default values allowed for typed arguments
-def f14(x: tuple[str, ...] = ("foo", "bar", "baz")) -> None: ...  # Y011 Only simple default values allowed for typed arguments
-def f15(x: set[str] = {"foo", "bar", "baz"}) -> None: ...  # Y011 Only simple default values allowed for typed arguments
+def f13(x: list[str] = ["foo", "bar", "baz"]) -> None: ...
+def f14(x: tuple[str, ...] = ("foo", "bar", "baz")) -> None: ...
+def f15(x: set[str] = {"foo", "bar", "baz"}) -> None: ...
+def f151(x: dict[int, int] = {1: 2}) -> None: ...
+# When parsed, this case results in `None` being placed in the `.keys` list for the `ast.Dict` node
+def f152(x: dict[int, int] = {1: 2, **{3: 4}}) -> None: ...  # Y011 Only simple default values allowed for typed arguments
+def f153(x: list[int] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]) -> None: ...  # Y011 Only simple default values allowed for typed arguments
+def f154(x: tuple[str, ...] = ("foo", ("bar", "baz"))) -> None: ...  # Y011 Only simple default values allowed for typed arguments
+def f141(x: list[int] = [*range(10)]) -> None: ...  # Y011 Only simple default values allowed for typed arguments
+def f142(x: list[int] = list(range(10))) -> None: ...  # Y011 Only simple default values allowed for typed arguments
 def f16(x: frozenset[bytes] = frozenset({b"foo", b"bar", b"baz"})) -> None: ...  # Y011 Only simple default values allowed for typed arguments
 def f17(x: str = "foo" + "bar") -> None: ...  # Y011 Only simple default values allowed for typed arguments
 def f18(x: str = b"foo" + b"bar") -> None: ...  # Y011 Only simple default values allowed for typed arguments

tests/quotes.pyi

@@ -9,8 +9,8 @@ __all__ += ["h"]
 __all__.extend(["i"])
 __all__.append("j")
 __all__.remove("j")
-__match_args__ = ('foo',)  # Y015 Only simple default values are allowed for assignments
-__slots__ = ('foo',)  # Y015 Only simple default values are allowed for assignments
+__match_args__ = ('foo',)  # Y052 Need type annotation for "__match_args__"
+__slots__ = ('foo',)  # Y052 Need type annotation for "__slots__"
 
 def f(x: "int"): ...  # Y020 Quoted annotations should never be used in stubs
 def g(x: list["int"]): ...  # Y020 Quoted annotations should never be used in stubs
@@ -26,7 +26,7 @@ Alias: TypeAlias = list["int"]  # Y020 Quoted annotations should never be used i
 class Child(list["int"]):  # Y020 Quoted annotations should never be used in stubs
     """Documented and guaranteed useful."""  # Y021 Docstrings should not be included in stubs
 
-    __all__ = ('foo',)  # Y015 Only simple default values are allowed for assignments
+    __all__ = ('foo',)  # Y052 Need type annotation for "__all__"
     __match_args__ = ('foo', 'bar')
     __slots__ = ('foo', 'bar')