Fix false-positive used-before-assignment in function returns

ChangeLog

@@ -22,6 +22,10 @@ Release date: Undefined
   only contain ``__version__`` (also accessible with ``pylint.__version__``), other meta-information are still
   accessible with ``import importlib;metadata.metadata('pylint')``.
 
+* Fix false-positive ``used-before-assignment`` in function returns.
+
+  Closes #4301
+
 
 What's New in Pylint 2.7.5?
 ===========================

pylint/checkers/variables.py

@@ -1457,7 +1457,12 @@ def _is_variable_violation(
                             and defnode.lineno == node.lineno
                             and isinstance(
                                 defstmt,
-                                (astroid.Assign, astroid.AnnAssign, astroid.AugAssign),
+                                (
+                                    astroid.Assign,
+                                    astroid.AnnAssign,
+                                    astroid.AugAssign,
+                                    astroid.Return,
+                                ),
                             )
                             and isinstance(defstmt.value, astroid.JoinedStr)
                         )

tests/functional/a/assignment_expression.py

@@ -1,5 +1,6 @@
 """Test assignment expressions"""
-# pylint: disable=missing-docstring,unused-argument,unused-import,invalid-name,blacklisted-name,unused-variable
+# pylint: disable=missing-docstring,unused-argument,unused-import,invalid-name
+# pylint: disable=blacklisted-name,unused-variable,pointless-statement
 import re
 
 if (a := True):
@@ -16,6 +17,15 @@
 c = [text for el in a if (text := el.strip()) == "b"]
 
 
+# check wrong usage
+assert err_a, (err_a := 2)  # [used-before-assignment]
+print(err_b and (err_b := 2))  # [used-before-assignment]
+values = (
+    err_c := err_d,  # [used-before-assignment]
+    err_d := 2,
+)
+
+
 # https://github.com/PyCQA/pylint/issues/3347
 s = 'foo' if (fval := lambda: 1) is None else fval
 
@@ -53,7 +63,7 @@ def func():
 
 
 # https://github.com/PyCQA/pylint/issues/3763
-foo if (foo := 3 - 2) > 0 else 0  # [pointless-statement]
+foo if (foo := 3 - 2) > 0 else 0
 
 
 # https://github.com/PyCQA/pylint/issues/4238
@@ -70,10 +80,7 @@ def func():
 )
 
 
-# check wrong usage
-assert err_a, (err_a := 2)  # [used-before-assignment]
-print(err_b and (err_b := 2))  # [used-before-assignment]
-values = (
-    err_c := err_d,  # [used-before-assignment]
-    err_d := 2,
-)
+# https://github.com/PyCQA/pylint/issues/4301
+def func2():
+    return f'The number {(count := 4)} ' \
+           f'is equal to {count}'

tests/functional/a/assignment_expression.txt

@@ -1,4 +1,3 @@
-pointless-statement:56:0::Statement seems to have no effect
-used-before-assignment:74:7::Using variable 'err_a' before assignment
-used-before-assignment:75:6::Using variable 'err_b' before assignment
-used-before-assignment:77:13::Using variable 'err_d' before assignment
+used-before-assignment:21:7::Using variable 'err_a' before assignment
+used-before-assignment:22:6::Using variable 'err_b' before assignment
+used-before-assignment:24:13::Using variable 'err_d' before assignment