From ee19aedc2fb8dd9f9d2268c0b04008b78ac712a4 Mon Sep 17 00:00:00 2001
From: David Euresti <david@euresti.com>
Date: Thu, 22 Mar 2018 10:02:37 -0700
Subject: [PATCH] Support factory= in attr plugin.

It works pretty much like default=
---
 mypy/plugins/attrs.py            |  6 ++++++
 test-data/unit/check-attr.test   | 12 ++++++++++++
 test-data/unit/lib-stub/attr.pyi |  8 ++++++--
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/mypy/plugins/attrs.py b/mypy/plugins/attrs.py
index 04b63e196ecb7..7ef56ae731a80 100644
--- a/mypy/plugins/attrs.py
+++ b/mypy/plugins/attrs.py
@@ -318,6 +318,12 @@ def _attribute_from_attrib_maker(ctx: 'mypy.plugin.ClassDefContext',
     init = _get_bool_argument(ctx, rvalue, 'init', True)
     # TODO: Check for attr.NOTHING
     attr_has_default = bool(_get_argument(rvalue, 'default'))
+    attr_has_factory = bool(_get_argument(rvalue, 'factory'))
+
+    if attr_has_default and attr_has_factory:
+        ctx.api.fail("Can't pass both `default` and `factory`.", rvalue)
+    elif attr_has_factory:
+        attr_has_default = attr_has_factory
 
     # If the type isn't set through annotation but is passed through `type=` use that.
     type_arg = _get_argument(rvalue, 'type')
diff --git a/test-data/unit/check-attr.test b/test-data/unit/check-attr.test
index 45a23ab56373f..73f86ffadbd4c 100644
--- a/test-data/unit/check-attr.test
+++ b/test-data/unit/check-attr.test
@@ -771,3 +771,15 @@ class FFrozen(F):
     def bar(self) -> bool:
         return self._cb(5, 6)
 [builtins fixtures/callable.pyi]
+
+[case testAttrsWithFactory]
+from typing import List
+import attr
+def my_factory() -> int:
+    return 7
+@attr.s
+class A:
+    x: List[int] = attr.ib(factory=list)
+    y: int = attr.ib(factory=my_factory)
+A()
+[builtins fixtures/list.pyi]
diff --git a/test-data/unit/lib-stub/attr.pyi b/test-data/unit/lib-stub/attr.pyi
index d62a99a685eb8..2f648b21c986b 100644
--- a/test-data/unit/lib-stub/attr.pyi
+++ b/test-data/unit/lib-stub/attr.pyi
@@ -13,7 +13,9 @@ def attr(default: Optional[_T] = ...,
          convert: Optional[Callable[[Any], _T]] = ...,
          metadata: Any = ...,
          type: Optional[Type[_T]] = ...,
-         converter: Optional[Callable[[Any], _T]] = ...) -> _T: ...
+         converter: Optional[Callable[[Any], _T]] = ...,
+         factory: Optional[Callable[[], _T]] = ...,
+         ) -> _T: ...
 @overload
 def attr(default: None = ...,
          validator: None = ...,
@@ -24,7 +26,9 @@ def attr(default: None = ...,
          convert: Optional[Callable[[Any], _T]] = ...,
          metadata: Any = ...,
          type: None = ...,
-         converter: None = ...) -> Any: ...
+         converter: None = ...,
+         factory: Optional[Callable[[], _T]] = ...,
+         ) -> Any: ...
 
 @overload
 def attributes(maybe_cls: _C,