Fix FP for used-before-assignment with assignment expressions in containers (#8253)

Author: jacobtylerwalls

doc/whatsnew/fragments/8252.false_positive

@@ -0,0 +1,4 @@
+Fix false positive for ``used-before-assignment`` for named expressions
+appearing after the first element in a list, tuple, or set.
+
+Closes #8252

pylint/checkers/variables.py

@@ -115,6 +115,15 @@
     astroid.nodes.node_classes.Dict,
 )
 
+NODES_WITH_VALUE_ATTR = (
+    nodes.Assign,
+    nodes.AnnAssign,
+    nodes.AugAssign,
+    nodes.Expr,
+    nodes.Return,
+    nodes.Match,
+)
+
 
 class VariableVisitConsumerAction(Enum):
     """Reported by _check_consumer() and its sub-methods to determine the
@@ -2139,17 +2148,7 @@ def _is_variable_violation(
                     # same line as the function definition
                     maybe_before_assign = False
                 elif (
-                    isinstance(
-                        defstmt,
-                        (
-                            nodes.Assign,
-                            nodes.AnnAssign,
-                            nodes.AugAssign,
-                            nodes.Expr,
-                            nodes.Return,
-                            nodes.Match,
-                        ),
-                    )
+                    isinstance(defstmt, NODES_WITH_VALUE_ATTR)
                     and VariablesChecker._maybe_used_and_assigned_at_once(defstmt)
                     and frame is defframe
                     and defframe.parent_of(node)
@@ -2245,13 +2244,15 @@ def _maybe_used_and_assigned_at_once(defstmt: nodes.Statement) -> bool:
         """
         if isinstance(defstmt, nodes.Match):
             return any(case.guard for case in defstmt.cases)
-        if isinstance(defstmt.value, nodes.BaseContainer) and defstmt.value.elts:
-            # The assignment must happen as part of the first element
-            # e.g. "assert (x:= True), x"
-            # NOT "assert x, (x:= True)"
-            value = defstmt.value.elts[0]
-        else:
-            value = defstmt.value
+        if isinstance(defstmt, nodes.IfExp):
+            return True
+        if isinstance(defstmt.value, nodes.BaseContainer):
+            return any(
+                VariablesChecker._maybe_used_and_assigned_at_once(elt)
+                for elt in defstmt.value.elts
+                if isinstance(elt, NODES_WITH_VALUE_ATTR + (nodes.IfExp, nodes.Match))
+            )
+        value = defstmt.value
         if isinstance(value, nodes.IfExp):
             return True
         if isinstance(value, nodes.Lambda) and isinstance(value.body, nodes.IfExp):

tests/functional/u/undefined/undefined_variable_py38.py

@@ -173,9 +173,13 @@ def expression_in_ternary_operator_inside_container_tuple():
     return [(val3, val3) if (val3 := 'something') else 'anything']
 
 
-def expression_in_ternary_operator_inside_container_wrong_position():
-    """2-element list where named expression comes too late"""
-    return [val3, val3 if (val3 := 'something') else 'anything']  # [used-before-assignment]
+def expression_in_ternary_operator_inside_container_later_position():
+    """
+    Named expression follows unrelated item in container.
+
+    If 23 is replaced with `val3`, there is currently a false negative,
+    but the false positive here is more important and likely to occur."""
+    return [23, val3 if (val3 := 'something') else 'anything']
 
 
 # Self-referencing

tests/functional/u/undefined/undefined_variable_py38.txt

@@ -6,6 +6,5 @@ undefined-variable:83:6:83:19::Undefined variable 'else_assign_1':INFERENCE
 undefined-variable:106:6:106:19::Undefined variable 'else_assign_2':INFERENCE
 used-before-assignment:141:10:141:16:type_annotation_used_improperly_after_comprehension:Using variable 'my_int' before assignment:HIGH
 used-before-assignment:148:10:148:16:type_annotation_used_improperly_after_comprehension_2:Using variable 'my_int' before assignment:HIGH
-used-before-assignment:178:12:178:16:expression_in_ternary_operator_inside_container_wrong_position:Using variable 'val3' before assignment:HIGH
-used-before-assignment:182:9:182:10::Using variable 'z' before assignment:HIGH
-used-before-assignment:189:6:189:19::Using variable 'NEVER_DEFINED' before assignment:CONTROL_FLOW
+used-before-assignment:186:9:186:10::Using variable 'z' before assignment:HIGH
+used-before-assignment:193:6:193:19::Using variable 'NEVER_DEFINED' before assignment:CONTROL_FLOW