Added `type` parameter to `attrs.field()` function (#1107)

* Added `type` parameter to `attrs.field` and test

* Added notice in examples.md

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

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* Added changelog entry

* Fixed docs

* Apply suggestions from code review

---------

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

changelog.d/1107.change.md

@@ -0,0 +1,3 @@
+Added *type* parameter to `attrs.field()` function for use with `attrs.make_class().
+
+Please note that type checkers ignore type metadata passed into `make_class()`, but it can be useful if you're wrapping _attrs_.

docs/examples.md

@@ -471,7 +471,7 @@ If you're the author of a third-party library with *attrs* integration, please s
 
 ## Types
 
-*attrs* also allows you to associate a type with an attribute using either the *type* argument to {func}`attr.ib` or using {pep}`526`-annotations:
+*attrs* also allows you to associate a type with an attribute using either the *type* argument to {func}`attr.ib` and {func}`attr.field` or using {pep}`526`-annotations:
 
 ```{doctest}
 >>> @define
@@ -626,11 +626,13 @@ Sometimes you may want to create a class programmatically.
 >>> from attrs import make_class
 >>> @define
 ... class C1:
-...     x = field()
+...     x = field(type=int)
 ...     y = field()
->>> C2 = make_class("C2", ["x", "y"])
+>>> C2 = make_class("C2", {"x": field(type=int), "y": field()})
 >>> fields(C1) == fields(C2)
 True
+>>> fields(C1).x.type
+<class 'int'>
 ```
 
 You can still have power over the attributes if you pass a dictionary of name: {func}`~attrs.field` mappings and can pass arguments to `@attr.s`:

src/attr/__init__.pyi

@@ -259,6 +259,7 @@ def field(
     order: Optional[bool] = ...,
     on_setattr: Optional[_OnSetAttrArgType] = ...,
     alias: Optional[str] = ...,
+    type: Optional[type] = ...,
 ) -> Any: ...
 
 # This form catches an explicit None or no default and infers the type from the
@@ -279,6 +280,7 @@ def field(
     order: Optional[_EqOrderType] = ...,
     on_setattr: Optional[_OnSetAttrArgType] = ...,
     alias: Optional[str] = ...,
+    type: Optional[type] = ...,
 ) -> _T: ...
 
 # This form catches an explicit default argument.
@@ -298,6 +300,7 @@ def field(
     order: Optional[_EqOrderType] = ...,
     on_setattr: Optional[_OnSetAttrArgType] = ...,
     alias: Optional[str] = ...,
+    type: Optional[type] = ...,
 ) -> _T: ...
 
 # This form covers type=non-Type: e.g. forward references (str), Any
@@ -317,6 +320,7 @@ def field(
     order: Optional[_EqOrderType] = ...,
     on_setattr: Optional[_OnSetAttrArgType] = ...,
     alias: Optional[str] = ...,
+    type: Optional[type] = ...,
 ) -> Any: ...
 @overload
 @__dataclass_transform__(order_default=True, field_descriptors=(attrib, field))

src/attr/_next_gen.py

@@ -167,6 +167,7 @@ def field(
     hash=None,
     init=True,
     metadata=None,
+    type=None,
     converter=None,
     factory=None,
     kw_only=False,
@@ -179,6 +180,10 @@ def field(
     Identical to `attr.ib`, except keyword-only and with some arguments
     removed.
 
+    .. versionadded:: 22.3.0
+       The *type* parameter has been re-added; mostly for
+       {func}`attrs.make_class`. Please note that type checkers ignore this
+       metadata.
     .. versionadded:: 20.1.0
     """
     return attrib(
@@ -188,6 +193,7 @@ def field(
         hash=hash,
         init=init,
         metadata=metadata,
+        type=type,
         converter=converter,
         factory=factory,
         kw_only=kw_only,

tests/test_next_gen.py

@@ -28,6 +28,16 @@ class TestNextGen:
         """
         C("1", 2)
 
+    def test_field_type(self):
+        """
+        Make class with attrs.field and type parameter.
+        """
+        classFields = {"testint": attrs.field(type=int)}
+
+        A = attrs.make_class("A", classFields)
+
+        assert int == attrs.fields(A).testint.type
+
     def test_no_slots(self):
         """
         slots can be deactivated.