Fixed an ``AttributeError`` caused by improper handling of ``dataclasses`` inference in ``pyreverse``

Close #3256

4 files changed, 34 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index fc7b8a1d1..e90c5e230 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -11,11 +11,14 @@ Release date: TBA
 
   Close #2242
 
-* Don't emit ``line-too-long`` for multilines when a
-  `pylint:disable=line-too-long` comment stands at their end
+* Don't emit ``line-too-long`` for multilines when `disable=line-too-long` comment stands at their end
 
   Close #2957
 
+* Fixed an ``AttributeError`` caused by improper handling of ``dataclasses`` inference in ``pyreverse``
+
+  Close #3256
+
 * Do not exempt bare except from ``undefined-variable`` and similar checks
 
   If a node was wrapped in a ``TryExcept``, ``pylint`` was taking a hint
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