From e169e83e52fedc6624235d45e8e8737294a0fedf Mon Sep 17 00:00:00 2001
From: Claudiu Popa <pcmanticore@gmail.com>
Date: Thu, 21 Nov 2019 09:45:33 +0100
Subject: Fixed an ``AttributeError`` caused by improper handling of
 ``dataclasses`` inference in ``pyreverse``

Close #3256
---
 ChangeLog                                             | 10 ++++++++++
 pylint/pyreverse/inspector.py                         |  3 ++-
 tests/regrtest_data/dataclasses_pyreverse/__init__.py | 13 +++++++++++++
 tests/unittest_pyreverse_diadefs.py                   | 14 ++++++++++++++
 4 files changed, 39 insertions(+), 1 deletion(-)
 create mode 100644 tests/regrtest_data/dataclasses_pyreverse/__init__.py

diff --git a/ChangeLog b/ChangeLog
index 0d6e61e22..74da1f374 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,16 @@
 Pylint's ChangeLog
 ------------------
 
+What's New in Pylint 2.4.5?
+===========================
+
+Release data: TBA
+
+* Fixed an ``AttributeError`` caused by improper handling of ``dataclasses`` inference in ``pyreverse``
+
+  Close #3256
+
+
 What's New in Pylint 2.4.4?
 ===========================
 Release date: 2019-11-13
diff --git a/pylint/pyreverse/inspector.py b/pylint/pyreverse/inspector.py
index 702b1084a..0a933afcc 100644
--- a/pylint/pyreverse/inspector.py
+++ b/pylint/pyreverse/inspector.py
@@ -163,7 +163,8 @@ class Linker(IdGeneratorMixIn, utils.LocalsVisitor):
         node.instance_attrs_type = collections.defaultdict(list)
         for assignattrs in node.instance_attrs.values():
             for assignattr in assignattrs:
-                self.handle_assignattr_type(assignattr, node)
+                if not isinstance(assignattr, astroid.Unknown):
+                    self.handle_assignattr_type(assignattr, node)
         # resolve implemented interface
         try:
             node.implements = list(interfaces(node, self.inherited_interfaces))
diff --git a/tests/regrtest_data/dataclasses_pyreverse/__init__.py b/tests/regrtest_data/dataclasses_pyreverse/__init__.py
new file mode 100644
index 000000000..e4c923343
--- /dev/null
+++ b/tests/regrtest_data/dataclasses_pyreverse/__init__.py
@@ -0,0 +1,13 @@
+from dataclasses import dataclass
+
+
+@dataclass
+class InventoryItem:
+    """Class for keeping track of an item in inventory."""
+
+    name: str
+    unit_price: float
+    quantity_on_hand: int = 0
+
+    def total_cost(self) -> float:
+        return self.unit_price * self.quantity_on_hand
diff --git a/tests/unittest_pyreverse_diadefs.py b/tests/unittest_pyreverse_diadefs.py
index 0659a5b11..307f22a94 100644
--- a/tests/unittest_pyreverse_diadefs.py
+++ b/tests/unittest_pyreverse_diadefs.py
@@ -13,6 +13,9 @@
 unit test for the extensions.diadefslib modules
 """
 
+import sys
+from pathlib import Path
+
 import astroid
 import pytest
 
@@ -173,3 +176,14 @@ def test_known_values2(HANDLER, PROJECT):
         (True, "DoNothing"),
         (True, "Specialization"),
     ]
+
+
+@pytest.mark.skipif(sys.version_info < (3, 8), reason="Requires dataclasses")
+def test_regression_dataclasses_inference(HANDLER):
+    project_path = Path("regrtest_data") / "dataclasses_pyreverse"
+    path = get_project(str(project_path))
+
+    cdg = ClassDiadefGenerator(Linker(path), HANDLER)
+    special = "regrtest_data.dataclasses_pyreverse.InventoryItem"
+    cd = cdg.class_diagram(path, special)
+    assert cd.title == special
-- 
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