A transform for the builtin `dataclasses` module was added.

This should address various `dataclasses` issues that were surfaced
even more after the release of pylint 2.4.0.
In the previous versions of `astroid`, annotated assign nodes were
allowed to be retrieved via `getattr()` but that no longer happens
with the latest `astroid` release, as those attribute are not actual
attributes, but rather virtual ones, thus an operation such as `getattr()`
does not make sense for them.

3 files changed, 98 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 4383c14c..1ceba6e0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,21 @@
 astroid's ChangeLog
 ===================
 
+What's New in astroid 2.3.1?
+============================
+Release Date: TBA
+
+* A transform for the builtin `dataclasses` module was added.
+
+  This should address various `dataclasses` issues that were surfaced
+  even more after the release of pylint 2.4.0.
+  In the previous versions of `astroid`, annotated assign nodes were
+  allowed to be retrieved via `getattr()` but that no longer happens
+  with the latest `astroid` release, as those attribute are not actual
+  attributes, but rather virtual ones, thus an operation such as `getattr()`
+  does not make sense for them.
+
+
 What's New in astroid 2.3.0?
 ============================
 Release Date: 2019-09-24
diff --git a/astroid/brain/brain_dataclasses.py b/astroid/brain/brain_dataclasses.py
new file mode 100644
index 00000000..7a25e0c6
--- /dev/null
+++ b/astroid/brain/brain_dataclasses.py
@@ -0,0 +1,50 @@
+# Licensed under the LGPL: https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html
+# For details: https://github.com/PyCQA/astroid/blob/master/COPYING.LESSER
+"""
+Astroid hook for the dataclasses library
+"""
+
+import astroid
+from astroid import MANAGER
+
+
+DATACLASSES_DECORATORS = frozenset(("dataclasses.dataclass", "dataclass"))
+
+
+def is_decorated_with_dataclass(node, decorator_names=DATACLASSES_DECORATORS):
+    """Return True if a decorated node has a `dataclass` decorator applied."""
+    if not node.decorators:
+        return False
+    for decorator_attribute in node.decorators.nodes:
+        if isinstance(decorator_attribute, astroid.Call):  # decorator with arguments
+            decorator_attribute = decorator_attribute.func
+        if decorator_attribute.as_string() in decorator_names:
+            return True
+    return False
+
+
+def dataclass_transform(node):
+    """Rewrite a dataclass to be easily understood by pylint"""
+
+    for assign_node in node.body:
+        if not isinstance(assign_node, (astroid.AnnAssign, astroid.Assign)):
+            continue
+
+        targets = (
+            assign_node.targets
+            if hasattr(assign_node, "targets")
+            else [assign_node.target]
+        )
+        for target in targets:
+            rhs_node = astroid.Unknown(
+                lineno=assign_node.lineno,
+                col_offset=assign_node.col_offset,
+                parent=assign_node,
+            )
+            node.instance_attrs[target.name] = [rhs_node]
+            node.locals[target.name] = [rhs_node]
+
+
+MANAGER.register_transform(
+    astroid.ClassDef, dataclass_transform, is_decorated_with_dataclass
+)
diff --git a/astroid/tests/unittest_brain.py b/astroid/tests/unittest_brain.py
index a045b194..9b29a280 100644
--- a/astroid/tests/unittest_brain.py
+++ b/astroid/tests/unittest_brain.py
@@ -1927,5 +1927,38 @@ def test_crypt_brain():
         assert attr in module
 
 
+@pytest.mark.skipif(sys.version_info < (3, 7), reason="Dataclasses were added in 3.7")
+def test_dataclasses():
+    code = """
+    import dataclasses
+    from dataclasses import dataclass
+
+    @dataclass
+    class InventoryItem:
+        name: str
+        quantity_on_hand: int = 0
+
+    @dataclasses.dataclass
+    class Other:
+        name: str
+    """
+
+    module = astroid.parse(code)
+    first = module["InventoryItem"]
+    second = module["Other"]
+
+    name = first.getattr("name")
+    assert len(name) == 1
+    assert isinstance(name[0], astroid.Unknown)
+
+    quantity_on_hand = first.getattr("quantity_on_hand")
+    assert len(quantity_on_hand) == 1
+    assert isinstance(quantity_on_hand[0], astroid.Unknown)
+
+    name = second.getattr("name")
+    assert len(name) == 1
+    assert isinstance(name[0], astroid.Unknown)
+
+
 if __name__ == "__main__":
     unittest.main()