Fix type annotations for converter types, considering the Converter class (#1373)

* Fix type annotations for converter types, considering the Converter class

Also consider that field() or attr.ib() takes a list or tuple of
converters as an implicit pipe, add type annotations for that syntax

* Fix expected mypy output with bad converters now that typing information has been expanded

Author: filbranden

src/attr/__init__.pyi

@@ -130,7 +130,7 @@ class Attribute(Generic[_T]):
     order: _EqOrderType
     hash: bool | None
     init: bool
-    converter: _ConverterType | Converter[Any, _T] | None
+    converter: Converter | None
     metadata: dict[Any, Any]
     type: type[_T] | None
     kw_only: bool
@@ -194,7 +194,10 @@ def attrib(
     init: bool = ...,
     metadata: Mapping[Any, Any] | None = ...,
     type: type[_T] | None = ...,
-    converter: _ConverterType | Converter[Any, _T] | None = ...,
+    converter: _ConverterType
+    | list[_ConverterType]
+    | tuple[_ConverterType]
+    | None = ...,
     factory: Callable[[], _T] | None = ...,
     kw_only: bool = ...,
     eq: _EqOrderType | None = ...,
@@ -214,7 +217,10 @@ def attrib(
     init: bool = ...,
     metadata: Mapping[Any, Any] | None = ...,
     type: type[_T] | None = ...,
-    converter: _ConverterType | Converter[Any, _T] | None = ...,
+    converter: _ConverterType
+    | list[_ConverterType]
+    | tuple[_ConverterType]
+    | None = ...,
     factory: Callable[[], _T] | None = ...,
     kw_only: bool = ...,
     eq: _EqOrderType | None = ...,
@@ -234,7 +240,10 @@ def attrib(
     init: bool = ...,
     metadata: Mapping[Any, Any] | None = ...,
     type: object = ...,
-    converter: _ConverterType | Converter[Any, _T] | None = ...,
+    converter: _ConverterType
+    | list[_ConverterType]
+    | tuple[_ConverterType]
+    | None = ...,
     factory: Callable[[], _T] | None = ...,
     kw_only: bool = ...,
     eq: _EqOrderType | None = ...,

src/attr/converters.pyi

@@ -10,4 +10,4 @@ def optional(converter: _ConverterType) -> _ConverterType: ...
 def default_if_none(default: _T) -> _ConverterType: ...
 @overload
 def default_if_none(*, factory: Callable[[], _T]) -> _ConverterType: ...
-def to_bool(val: str) -> bool: ...
+def to_bool(val: str | int | bool) -> bool: ...

src/attrs/__init__.pyi

@@ -51,7 +51,7 @@ _C = TypeVar("_C", bound=type)
 
 _EqOrderType = bool | Callable[[Any], Any]
 _ValidatorType = Callable[[Any, "Attribute[_T]", _T], Any]
-_ConverterType = Callable[[Any], Any]
+_ConverterType = Callable[[Any], Any] | Converter[Any, _T]
 _ReprType = Callable[[Any], str]
 _ReprArgType = bool | _ReprType
 _OnSetAttrType = Callable[[Any, "Attribute[Any]", Any], Any]
@@ -94,7 +94,10 @@ def field(
     hash: bool | None = ...,
     init: bool = ...,
     metadata: Mapping[Any, Any] | None = ...,
-    converter: _ConverterType | Converter[Any, _T] | None = ...,
+    converter: _ConverterType
+    | list[_ConverterType]
+    | tuple[_ConverterType]
+    | None = ...,
     factory: Callable[[], _T] | None = ...,
     kw_only: bool = ...,
     eq: _EqOrderType | None = ...,
@@ -114,7 +117,10 @@ def field(
     hash: bool | None = ...,
     init: bool = ...,
     metadata: Mapping[Any, Any] | None = ...,
-    converter: _ConverterType | Converter[Any, _T] | None = ...,
+    converter: _ConverterType
+    | list[_ConverterType]
+    | tuple[_ConverterType]
+    | None = ...,
     factory: Callable[[], _T] | None = ...,
     kw_only: bool = ...,
     eq: _EqOrderType | None = ...,
@@ -134,7 +140,10 @@ def field(
     hash: bool | None = ...,
     init: bool = ...,
     metadata: Mapping[Any, Any] | None = ...,
-    converter: _ConverterType | Converter[Any, _T] | None = ...,
+    converter: _ConverterType
+    | list[_ConverterType]
+    | tuple[_ConverterType]
+    | None = ...,
     factory: Callable[[], _T] | None = ...,
     kw_only: bool = ...,
     eq: _EqOrderType | None = ...,

tests/test_mypy.yml

@@ -788,9 +788,9 @@
     reveal_type(A)
   out: |
     main:15: error: Cannot determine __init__ type from converter  [misc]
-    main:15: error: Argument "converter" has incompatible type "Callable[[], str]"; expected "Callable[[Any], Any] | Converter[Any, Never] | None"  [arg-type]
+    main:15: error: Argument "converter" has incompatible type "Callable[[], str]"; expected "Callable[[Any], Any] | Converter[Any, Any] | list[Callable[[Any], Any] | Converter[Any, Any]] | tuple[Callable[[Any], Any] | Converter[Any, Any]] | None"  [arg-type]
     main:16: error: Cannot determine __init__ type from converter  [misc]
-    main:16: error: Argument "converter" has incompatible type overloaded function; expected "Callable[[Any], Any] | Converter[Any, Never] | None"  [arg-type]
+    main:16: error: Argument "converter" has incompatible type overloaded function; expected "Callable[[Any], Any] | Converter[Any, Any] | list[Callable[[Any], Any] | Converter[Any, Any]] | tuple[Callable[[Any], Any] | Converter[Any, Any]] | None"  [arg-type]
     main:17: note: Revealed type is "def (bad: Any, bad_overloaded: Any) -> main.A"
 
 - case: testAttrsUsingBadConverterReprocess
@@ -816,9 +816,9 @@
     reveal_type(A)
   out: |
     main:16: error: Cannot determine __init__ type from converter  [misc]
-    main:16: error: Argument "converter" has incompatible type "Callable[[], str]"; expected "Callable[[Any], Any] | Converter[Any, Never] | None"  [arg-type]
+    main:16: error: Argument "converter" has incompatible type "Callable[[], str]"; expected "Callable[[Any], Any] | Converter[Any, Any] | list[Callable[[Any], Any] | Converter[Any, Any]] | tuple[Callable[[Any], Any] | Converter[Any, Any]] | None"  [arg-type]
     main:17: error: Cannot determine __init__ type from converter  [misc]
-    main:17: error: Argument "converter" has incompatible type overloaded function; expected "Callable[[Any], Any] | Converter[Any, Never] | None"  [arg-type]
+    main:17: error: Argument "converter" has incompatible type overloaded function; expected "Callable[[Any], Any] | Converter[Any, Any] | list[Callable[[Any], Any] | Converter[Any, Any]] | tuple[Callable[[Any], Any] | Converter[Any, Any]] | None"  [arg-type]
     main:18: note: Revealed type is "def (bad: Any, bad_overloaded: Any) -> main.A"
 
 - case: testAttrsUsingUnsupportedConverter

tests/typing_example.py

@@ -133,40 +133,52 @@ class AliasExample:
 attr.fields(AliasExample).without_alias.alias
 attr.fields(AliasExample)._with_alias.alias
 
+
 # Converters
-# XXX: Currently converters can only be functions so none of this works
-# although the stubs should be correct.
 
-# @attr.s
-# class ConvCOptional:
-#     x: Optional[int] = attr.ib(converter=attr.converters.optional(int))
 
+@attr.s
+class ConvCOptional:
+    x: int | None = attr.ib(converter=attr.converters.optional(int))
 
-# ConvCOptional(1)
-# ConvCOptional(None)
 
+ConvCOptional(1)
+ConvCOptional(None)
 
+
+# XXX: Fails with E: Unsupported converter, only named functions, types and lambdas are currently supported  [misc]
+# See https://github.com/python/mypy/issues/15736
+#
+# @attr.s
+# class ConvCPipe:
+#     x: str = attr.ib(converter=attr.converters.pipe(int, str))
+#
+#
+# ConvCPipe(3.4)
+# ConvCPipe("09")
+#
+#
 # @attr.s
 # class ConvCDefaultIfNone:
 #     x: int = attr.ib(converter=attr.converters.default_if_none(42))
-
-
+#
+#
 # ConvCDefaultIfNone(1)
 # ConvCDefaultIfNone(None)
 
 
-# @attr.s
-# class ConvCToBool:
-#     x: int = attr.ib(converter=attr.converters.to_bool)
+@attr.s
+class ConvCToBool:
+    x: int = attr.ib(converter=attr.converters.to_bool)
 
 
-# ConvCToBool(1)
-# ConvCToBool(True)
-# ConvCToBool("on")
-# ConvCToBool("yes")
-# ConvCToBool(0)
-# ConvCToBool(False)
-# ConvCToBool("n")
+ConvCToBool(1)
+ConvCToBool(True)
+ConvCToBool("on")
+ConvCToBool("yes")
+ConvCToBool(0)
+ConvCToBool(False)
+ConvCToBool("n")
 
 
 # Validators