Make ``used-before-assignment`` consider classes in method annotation and defaults (#5184)

This closes #3771

Co-authored-by: Marc Mueller <30130371+cdce8p@users.noreply.github.com>

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

10 files changed, 126 insertions, 10 deletions

diff --git a/ChangeLog b/ChangeLog
index 634e887b6..13a2d977f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -31,6 +31,11 @@ Release date: TBA
 
   Closes #4031
 
+* ``used-before-assignment`` now correctly considers references to classes as type annotation
+  or default values in first-level methods
+
+  Closes #3771
+
 * 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 f98406800..2a6c321fe 100644
--- a/doc/whatsnew/2.12.rst
+++ b/doc/whatsnew/2.12.rst
@@ -77,6 +77,11 @@ Other Changes
 
   Closes #4031
 
+* ``used-before-assignment`` now correctly considers references to classes as type annotation
+  or default values in first-level methods
+
+  Closes #3771
+
 * Fix double emitting of ``not-callable`` on inferrable ``properties``
 
   Closes #4426
diff --git a/pylint/checkers/variables.py b/pylint/checkers/variables.py
index 1d78184c8..c8d1f4f5d 100644
--- a/pylint/checkers/variables.py
+++ b/pylint/checkers/variables.py
@@ -59,6 +59,7 @@ import copy
 import itertools
 import os
 import re
+import sys
 from functools import lru_cache
 from typing import DefaultDict, List, Tuple
 
@@ -71,6 +72,11 @@ from pylint.constants import PY39_PLUS
 from pylint.interfaces import HIGH, INFERENCE, INFERENCE_FAILURE, IAstroidChecker
 from pylint.utils import get_global_option
 
+if sys.version_info >= (3, 8):
+    from typing import Literal
+else:
+    from typing_extensions import Literal
+
 SPECIAL_OBJ = re.compile("^_{2}[a-z]+_{2}$")
 FUTURE = "__future__"
 # regexp for ignored argument name
@@ -1195,6 +1201,16 @@ class VariablesChecker(BaseChecker):
                             )
                 elif self._is_only_type_assignment(node, defstmt):
                     self.add_message("undefined-variable", node=node, args=node.name)
+                elif isinstance(defstmt, nodes.ClassDef):
+                    is_first_level_ref = self._is_first_level_self_reference(
+                        node, defstmt
+                    )
+                    if is_first_level_ref == 2:
+                        self.add_message(
+                            "used-before-assignment", node=node, args=node.name
+                        )
+                    if is_first_level_ref:
+                        break
 
             current_consumer.mark_as_consumed(node.name, found_nodes)
             # check it's not a loop variable used outside the loop
@@ -1569,6 +1585,32 @@ class VariablesChecker(BaseChecker):
                     return False
         return True
 
+    @staticmethod
+    def _is_first_level_self_reference(
+        node: nodes.Name, defstmt: nodes.ClassDef
+    ) -> Literal[0, 1, 2]:
+        """Check if a first level method's annotation or default values
+        refers to its own class.
+
+        Return values correspond to:
+            0 = Continue
+            1 = Break
+            2 = Break + emit message
+        """
+        if node.frame().parent == defstmt:
+            # Check if used as type annotation
+            # Break but don't emit message if postponed evaluation is enabled
+            if utils.is_node_in_type_annotation_context(node):
+                if not utils.is_postponed_evaluation_enabled(node):
+                    return 2
+                return 1
+            # Check if used as default value by calling the class
+            if isinstance(node.parent, nodes.Call) and isinstance(
+                node.parent.parent, nodes.Arguments
+            ):
+                return 2
+        return 0
+
     def _ignore_class_scope(self, node):
         """
         Return True if the node is in a local class scope, as an assignment.
diff --git a/tests/functional/u/use/used_before_assignement.py b/tests/functional/u/use/used_before_assignement.py
deleted file mode 100644
index 285f3d180..000000000
--- a/tests/functional/u/use/used_before_assignement.py
+++ /dev/null
@@ -1,8 +0,0 @@
-"""pylint doesn't see the NameError in this module"""
-#pylint: disable=consider-using-f-string
-__revision__ = None
-
-MSG = "hello %s" % MSG  # [used-before-assignment]
-
-MSG2 = ("hello %s" %
-        MSG2) # [used-before-assignment]
diff --git a/tests/functional/u/use/used_before_assignement.txt b/tests/functional/u/use/used_before_assignement.txt
deleted file mode 100644
index d19fe322a..000000000
--- a/tests/functional/u/use/used_before_assignement.txt
+++ /dev/null
@@ -1,2 +0,0 @@
-used-before-assignment:5:19::Using variable 'MSG' before assignment
-used-before-assignment:8:8::Using variable 'MSG2' before assignment
diff --git a/tests/functional/u/use/used_before_assignment.py b/tests/functional/u/use/used_before_assignment.py
new file mode 100644
index 000000000..376515c54
--- /dev/null
+++ b/tests/functional/u/use/used_before_assignment.py
@@ -0,0 +1,38 @@
+"""pylint doesn't see the NameError in this module"""
+# pylint: disable=consider-using-f-string, missing-function-docstring
+__revision__ = None
+
+from typing import List
+
+
+MSG = "hello %s" % MSG  # [used-before-assignment]
+
+MSG2 = "hello %s" % MSG2  # [used-before-assignment]
+
+
+class MyClass:
+    """Type annotation or default values for first level methods can't refer to their own class"""
+
+    def incorrect_typing_method(
+        self, other: MyClass  # [used-before-assignment]
+    ) -> bool:
+        return self == other
+
+    def incorrect_nested_typing_method(
+        self, other: List[MyClass]  # [used-before-assignment]
+    ) -> bool:
+        return self == other[0]
+
+    def incorrect_default_method(
+        self, other=MyClass()  # [used-before-assignment]
+    ) -> bool:
+        return self == other
+
+    def correct_string_typing_method(self, other: "MyClass") -> bool:
+        return self == other
+
+    def correct_inner_typing_method(self) -> bool:
+        def inner_method(self, other: MyClass) -> bool:
+            return self == other
+
+        return inner_method(self, MyClass())
diff --git a/tests/functional/u/use/used_before_assignment.txt b/tests/functional/u/use/used_before_assignment.txt
new file mode 100644
index 000000000..096144dc7
--- /dev/null
+++ b/tests/functional/u/use/used_before_assignment.txt
@@ -0,0 +1,5 @@
+used-before-assignment:8:19::Using variable 'MSG' before assignment:HIGH
+used-before-assignment:10:20::Using variable 'MSG2' before assignment:HIGH
+used-before-assignment:17:21:MyClass.incorrect_typing_method:Using variable 'MyClass' before assignment:HIGH
+used-before-assignment:22:26:MyClass.incorrect_nested_typing_method:Using variable 'MyClass' before assignment:HIGH
+used-before-assignment:27:20:MyClass.incorrect_default_method:Using variable 'MyClass' before assignment:HIGH
diff --git a/tests/functional/u/use/used_before_assignment_py37.py b/tests/functional/u/use/used_before_assignment_py37.py
new file mode 100644
index 000000000..e17c345a9
--- /dev/null
+++ b/tests/functional/u/use/used_before_assignment_py37.py
@@ -0,0 +1,28 @@
+"""Tests for used-before-assignment with functions added in python 3.7"""
+# pylint: disable=missing-function-docstring
+from __future__ import annotations
+from typing import List
+
+
+class MyClass:
+    """With the future import only default values can't refer to the base class"""
+
+    def correct_typing_method(self, other: MyClass) -> bool:
+        return self == other
+
+    def second_correct_typing_method(self, other: List[MyClass]) -> bool:
+        return self == other[0]
+
+    def incorrect_default_method(
+        self, other=MyClass() # [used-before-assignment]
+    ) -> bool:
+        return self == other
+
+    def correct_string_typing_method(self, other: "MyClass") -> bool:
+        return self == other
+
+    def correct_inner_typing_method(self) -> bool:
+        def inner_method(self, other: MyClass) -> bool:
+            return self == other
+
+        return inner_method(self, MyClass())
diff --git a/tests/functional/u/use/used_before_assignment_py37.rc b/tests/functional/u/use/used_before_assignment_py37.rc
new file mode 100644
index 000000000..a17bb22da
--- /dev/null
+++ b/tests/functional/u/use/used_before_assignment_py37.rc
@@ -0,0 +1,2 @@
+[testoptions]
+min_pyver=3.7
diff --git a/tests/functional/u/use/used_before_assignment_py37.txt b/tests/functional/u/use/used_before_assignment_py37.txt
new file mode 100644
index 000000000..ec4fb036b
--- /dev/null
+++ b/tests/functional/u/use/used_before_assignment_py37.txt
@@ -0,0 +1 @@
+used-before-assignment:17:20:MyClass.incorrect_default_method:Using variable 'MyClass' before assignment:HIGH