Fix used-before-assignment false positive for walrus operators in ifs (#8029) (#8033)

Co-authored-by: Pierre Sassoulas <[email protected]>
(cherry picked from commit 6ac908f)

Co-authored-by: Zen Lee <[email protected]>

Author: github-actions[bot]

doc/whatsnew/fragments/7779.false_positive

@@ -0,0 +1,4 @@
+Fixes ``used-before-assignment`` false positive when the walrus operator
+is used in a ternary operator.
+
+Closes #7779

pylint/checkers/variables.py

@@ -2055,9 +2055,16 @@ def _maybe_used_and_assigned_at_once(defstmt: nodes.Statement) -> bool:
             return True
         if isinstance(value, nodes.Lambda) and isinstance(value.body, nodes.IfExp):
             return True
-        return isinstance(value, nodes.Call) and (
-            any(isinstance(kwarg.value, nodes.IfExp) for kwarg in value.keywords)
-            or any(isinstance(arg, nodes.IfExp) for arg in value.args)
+        if not isinstance(value, nodes.Call):
+            return False
+        return any(
+            any(isinstance(kwarg.value, nodes.IfExp) for kwarg in call.keywords)
+            or any(isinstance(arg, nodes.IfExp) for arg in call.args)
+            or (
+                isinstance(call.func, nodes.Attribute)
+                and isinstance(call.func.expr, nodes.IfExp)
+            )
+            for call in value.nodes_of_class(klass=nodes.Call)
         )
 
     def _is_only_type_assignment(

tests/functional/u/used/used_before_assignment_ternary.py

@@ -0,0 +1,41 @@
+"""Tests for used-before-assignment false positive from ternary expression with walrus operator"""
+# pylint: disable=unnecessary-lambda-assignment, unused-variable, disallowed-name, invalid-name
+
+def invalid():
+    """invalid cases that will trigger used-before-assignment"""
+    var = foo(a, '', '')  # [used-before-assignment]
+    print(str(1 if (a:=-1) else 0))
+    var = bar(b)  # [used-before-assignment]
+    var = c*c  # [used-before-assignment]
+    var = 1 if (b:=-1) else 0
+    var = 1 if (c:=-1) else 0
+
+def attribute_call_valid():
+    """assignment with attribute calls"""
+    var = (a if (a:='a') else '').lower()
+    var = ('' if (b:='b') else b).lower()
+    var = (c if (c:='c') else c).upper().lower().replace('', '').strip()
+    var = ''.strip().replace('', '' + (e if (e:='e') else '').lower())
+
+def function_call_arg_valid():
+    """assignment as function call arguments"""
+    var = str(a if (a:='a') else '')
+    var = str('' if (b:='b') else b)
+    var = foo(1, c if (c:=1) else 0, 1)
+    print(foo('', '', foo('', str(int(d if (d:='1') else '')), '')))
+
+def function_call_keyword_valid():
+    """assignment as function call keywords"""
+    var = foo(x=a if (a:='1') else '', y='', z='')
+    var = foo(x='', y=foo(x='', y='', z=b if (b:='1') else ''), z='')
+
+def complex_valid():
+    """assignment within complex call expression"""
+    var = str(bar(bar(a if (a:=1) else 0))).lower().upper()
+    print(foo(x=foo(''.replace('', str(b if (b:=1) else 0).upper()), '', z=''), y='', z=''))
+
+def foo(x, y, z):
+    """helper function for tests"""
+    return x+y+z
+
+bar = lambda x : x

tests/functional/u/used/used_before_assignment_ternary.rc

@@ -0,0 +1,2 @@
+[testoptions]
+min_pyver=3.8

tests/functional/u/used/used_before_assignment_ternary.txt

@@ -0,0 +1,3 @@
+used-before-assignment:6:14:6:15:invalid:Using variable 'a' before assignment:HIGH
+used-before-assignment:8:14:8:15:invalid:Using variable 'b' before assignment:HIGH
+used-before-assignment:9:10:9:11:invalid:Using variable 'c' before assignment:HIGH