Annotate __init__ with type hints

This just adds the annotations found at run-time to the
`__annotations__` attribute of the created `__init__` function

Fixes #249

src/attr/_make.py

@@ -1034,7 +1034,7 @@ def _make_init(attrs, post_init, frozen, slots, super_attr_map):
         sha1.hexdigest()
     )
 
-    script, globs = _attrs_to_init_script(
+    script, globs, annotations = _attrs_to_init_script(
         attrs,
         frozen,
         slots,
@@ -1063,7 +1063,9 @@ def _make_init(attrs, post_init, frozen, slots, super_attr_map):
         unique_filename,
     )
 
-    return locs["__init__"]
+    __init__ = locs["__init__"]
+    __init__.__annotations__ = annotations
+    return __init__
 
 
 def _add_init(cls, frozen):
@@ -1259,6 +1261,7 @@ def fmt_setter_with_converter(attr_name, value_var):
     # This is a dictionary of names to validator and converter callables.
     # Injecting this into __init__ globals lets us avoid lookups.
     names_for_globals = {}
+    annotations = {}
 
     for a in attrs:
         if a.validator:
@@ -1349,6 +1352,9 @@ def fmt_setter_with_converter(attr_name, value_var):
             else:
                 lines.append(fmt_setter(attr_name, arg_name))
 
+        if a.init is True and a.converter is None and a.type is not None:
+            annotations[arg_name] = a.type
+
     if attrs_to_validate:  # we can skip this if there are no validators.
         names_for_globals["_config"] = _config
         lines.append("if _config._run_validators is True:")
@@ -1368,7 +1374,7 @@ def __init__(self, {args}):
 """.format(
         args=", ".join(args),
         lines="\n    ".join(lines) if lines else "pass",
-    ), names_for_globals
+    ), names_for_globals, annotations
 
 
 class Attribute(object):

tests/test_annotations.py

@@ -13,6 +13,8 @@
 
 from attr.exceptions import UnannotatedAttributeError
 
+NoneType = type(None)
+
 
 class TestAnnotations:
     """
@@ -32,6 +34,7 @@ class C:
         assert int is attr.fields(C).x.type
         assert str is attr.fields(C).y.type
         assert None is attr.fields(C).z.type
+        assert C.__init__.__annotations__ == {'x': int, 'y': str}
 
     def test_catches_basic_type_conflict(self):
         """
@@ -57,6 +60,8 @@ class C:
 
         assert typing.List[int] is attr.fields(C).x.type
         assert typing.Optional[str] is attr.fields(C).y.type
+        assert C.__init__.__annotations__ == {'x': typing.List[int],
+                                              'y': typing.Union[str, NoneType]}
 
     def test_only_attrs_annotations_collected(self):
         """
@@ -68,6 +73,7 @@ class C:
             y: int
 
         assert 1 == len(attr.fields(C))
+        assert C.__init__.__annotations__ == {'x': typing.List[int]}
 
     @pytest.mark.parametrize("slots", [True, False])
     def test_auto_attribs(self, slots):
@@ -115,6 +121,14 @@ class C:
             i.y = 23
             assert 23 == i.y
 
+        assert C.__init__.__annotations__ == {
+            'a': int,
+            'x': typing.List[int],
+            'y': int,
+            'z': int,
+            'foo': typing.Any
+        }
+
     @pytest.mark.parametrize("slots", [True, False])
     def test_auto_attribs_unannotated(self, slots):
         """
@@ -154,3 +168,14 @@ class C(A):
 
         assert "B(a=1, b=2)" == repr(B())
         assert "C(a=1)" == repr(C())
+
+        assert A.__init__.__annotations__ == {
+            'a': int,
+        }
+        assert B.__init__.__annotations__ == {
+            'a': int,
+            'b': int,
+        }
+        assert C.__init__.__annotations__ == {
+            'a': int,
+        }