From 1daee40d6f1cf3d379396dc272c123d987ad4cdd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dani=C3=ABl=20van=20Noord?=
 <13665637+DanielNoord@users.noreply.github.com>
Date: Mon, 18 Oct 2021 14:58:01 +0200
Subject: Make ``undefined-variable`` check line numbers of metaclass
 parameters

---
 ChangeLog                                             |  5 +++++
 doc/whatsnew/2.12.rst                                 |  5 +++++
 pylint/checkers/variables.py                          | 19 +++++++++++++------
 .../functional/u/undefined/undefined_variable_py30.py | 10 ++++++++++
 .../u/undefined/undefined_variable_py30.txt           |  1 +
 5 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index f9eba4227..f26007d1e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -26,6 +26,11 @@ Release date: TBA
 
   Closes #5140
 
+* ``undefined-variable`` now correctly considers the line numbering and order of classes
+  used in metaclass declarations
+
+  Closes #4031
+
 * Fix bug with importing namespace packages with relative imports
 
   Closes #2967 and #5131
diff --git a/doc/whatsnew/2.12.rst b/doc/whatsnew/2.12.rst
index 54214ac99..be1e5245c 100644
--- a/doc/whatsnew/2.12.rst
+++ b/doc/whatsnew/2.12.rst
@@ -69,3 +69,8 @@ Other Changes
   and never get assigned a value
 
   Closes #5140
+
+* ``undefined-variable`` now correctly considers the line numbering and order of classes
+  used in metaclass declarations
+
+  Closes #4031
diff --git a/pylint/checkers/variables.py b/pylint/checkers/variables.py
index ef53f19cb..1d78184c8 100644
--- a/pylint/checkers/variables.py
+++ b/pylint/checkers/variables.py
@@ -2213,23 +2213,30 @@ class VariablesChecker(BaseChecker):
         elif metaclass:
             name = metaclass.root().name
 
-        found = None
+        found = False
         name = METACLASS_NAME_TRANSFORMS.get(name, name)
         if name:
             # check enclosing scopes starting from most local
             for scope_locals, _, _ in self._to_consume[::-1]:
-                found = scope_locals.get(name)
-                if found:
-                    consumed.append((scope_locals, name))
+                found_nodes = scope_locals.get(name, [])
+                for found_node in found_nodes:
+                    if found_node.lineno <= klass.lineno:
+                        consumed.append((scope_locals, name))
+                        found = True
+                        break
+            # Check parent scope
+            nodes_in_parent_scope = parent_node.locals.get(name, [])
+            for found_node_parent in nodes_in_parent_scope:
+                if found_node_parent.lineno <= klass.lineno:
+                    found = True
                     break
         if (
-            found is None
+            not found
             and not metaclass
             and not (
                 name in nodes.Module.scope_attrs
                 or utils.is_builtin(name)
                 or name in self.config.additional_builtins
-                or name in parent_node.locals
             )
         ):
             self.add_message("undefined-variable", node=klass, args=(name,))
diff --git a/tests/functional/u/undefined/undefined_variable_py30.py b/tests/functional/u/undefined/undefined_variable_py30.py
index 556b1028b..b9b64ec5e 100644
--- a/tests/functional/u/undefined/undefined_variable_py30.py
+++ b/tests/functional/u/undefined/undefined_variable_py30.py
@@ -96,3 +96,13 @@ class MetaClass(type):
 
 class InheritingClass(metaclass=MetaClass, parameter=variable):  # [undefined-variable]
     pass
+
+
+# Test for #4031
+# https://github.com/PyCQA/pylint/issues/4031
+class Inheritor(metaclass=DefinedTooLate ): # [undefined-variable]
+    pass
+
+
+class DefinedTooLate():
+    pass
diff --git a/tests/functional/u/undefined/undefined_variable_py30.txt b/tests/functional/u/undefined/undefined_variable_py30.txt
index 4756b5cd2..e0a942202 100644
--- a/tests/functional/u/undefined/undefined_variable_py30.txt
+++ b/tests/functional/u/undefined/undefined_variable_py30.txt
@@ -7,3 +7,4 @@ undefined-variable:57:31:FalsePositive342.test_bad2:Undefined variable 'trop2':H
 undefined-variable:63:0:Bad:Undefined variable 'ABCMet':HIGH
 undefined-variable:66:0:SecondBad:Undefined variable 'ab':HIGH
 undefined-variable:97:53:InheritingClass:Undefined variable 'variable':HIGH
+undefined-variable:103:0:Inheritor:Undefined variable 'DefinedTooLate':HIGH
-- 
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