From c5288f966a6d9c3d22152657605d4ca45c52c8c3 Mon Sep 17 00:00:00 2001
From: Ryan Gonzalez <rymg19@gmail.com>
Date: Sun, 7 Jul 2019 20:29:04 -0500
Subject: [PATCH] Don't define a duplicate __init__ for dataclasses

Closes #6399.
---
 mypy/plugins/dataclasses.py           |  2 +-
 test-data/unit/check-dataclasses.test | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/mypy/plugins/dataclasses.py b/mypy/plugins/dataclasses.py
index 7646c1dfacc4f..e8d2eb324a07e 100644
--- a/mypy/plugins/dataclasses.py
+++ b/mypy/plugins/dataclasses.py
@@ -92,7 +92,7 @@ def transform(self) -> None:
             'frozen': _get_decorator_bool_argument(self._ctx, 'frozen', False),
         }
 
-        if decorator_arguments['init']:
+        if decorator_arguments['init'] and info.get('__init__') is None:
             add_method(
                 ctx,
                 '__init__',
diff --git a/test-data/unit/check-dataclasses.test b/test-data/unit/check-dataclasses.test
index 288c37664d22a..2000d57ab7ffe 100644
--- a/test-data/unit/check-dataclasses.test
+++ b/test-data/unit/check-dataclasses.test
@@ -16,6 +16,21 @@ Person('Jonh', 21, None)  # E: Too many arguments for "Person"
 
 [builtins fixtures/list.pyi]
 
+[case testDataclassesCustomInit]
+# flags: --python-version 3.6
+from dataclasses import dataclass
+
+@dataclass
+class A:
+    a: int
+
+    def __init__(self, a: str) -> None:
+        pass
+
+A('1')
+
+[builtins fixtures/list.pyi]
+
 [case testDataclassesBasicInheritance]
 # flags: --python-version 3.6
 from dataclasses import dataclass