Fix attrs.field(converter=...) type annotations (#1461)

* Fix `attrs.field(converter=...)` type annotations

    Converters can currently be specified as `_ConverterType`,
    `list[_ConverterType]`, or `tuple[_ConverterType]`. The last of
    these does not mean "tuple of `_ConverterType` instances" as was
    likely intended; it specifies a tuple with exactly one
    `_ConverterType` element. The correct form for a `tuple` with any
    number of instances is `tuple[_ConverterType, ...]`.

* Add to `changelog.d`

* Add regression test for PR 1461

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update changelog.d/1461.change.md

* Update tests/test_pyright.py

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Hynek Schlawack <hs@ox.cx>

Author: 3 people

changelog.d/1461.change.md

@@ -0,0 +1,2 @@
+Fixed annotations for `attrs.field(converter=...)`.
+Previously, a `tuple` of converters was only accepted if it had exactly one element.

src/attrs/__init__.pyi

@@ -98,7 +98,7 @@ def field(
     metadata: Mapping[Any, Any] | None = ...,
     converter: _ConverterType
     | list[_ConverterType]
-    | tuple[_ConverterType]
+    | tuple[_ConverterType, ...]
     | None = ...,
     factory: Callable[[], _T] | None = ...,
     kw_only: bool | None = ...,
@@ -121,7 +121,7 @@ def field(
     metadata: Mapping[Any, Any] | None = ...,
     converter: _ConverterType
     | list[_ConverterType]
-    | tuple[_ConverterType]
+    | tuple[_ConverterType, ...]
     | None = ...,
     factory: Callable[[], _T] | None = ...,
     kw_only: bool | None = ...,
@@ -144,7 +144,7 @@ def field(
     metadata: Mapping[Any, Any] | None = ...,
     converter: _ConverterType
     | list[_ConverterType]
-    | tuple[_ConverterType]
+    | tuple[_ConverterType, ...]
     | None = ...,
     factory: Callable[[], _T] | None = ...,
     kw_only: bool | None = ...,

tests/test_pyright.py

@@ -106,3 +106,36 @@ def test_pyright_attrsinstance_compat(tmp_path):
         )
     }
     assert diagnostics == expected_diagnostics
+
+
+def test_pyright_field_converters_tuple(tmp_path):
+    """
+    Test that `field(converter=(_, _, ...))` raises no FPs in Pyright.
+    """
+    test_pyright_field_converters_tuple_path = (
+        tmp_path / "test_pyright_field_converters_tuple.py"
+    )
+    test_pyright_field_converters_tuple_path.write_text(
+        """\
+import attrs
+
+
+def square(value: int) -> int:
+    return value * value
+
+def negate(value: int) -> int:
+    return -value
+
+
+@attrs.define
+class SomeClass:
+
+    value: int = attrs.field(converter=(square, negate))
+"""
+    )
+
+    diagnostics = parse_pyright_output(
+        test_pyright_field_converters_tuple_path
+    )
+
+    assert not diagnostics