Fix false positive superfluous parens for walrus operator

Close pylint-dev#3383

ChangeLog

@@ -30,6 +30,11 @@ Release date: TBA
 
 * Fix `pre-commit` config that could lead to undetected duplicate lines of code
 
+* Fix superfluous-parens false-positive for the walrus operator
+
+  Close #3383
+
+
 What's New in Pylint 2.5.3?
 ===========================
 

pylint/checkers/format.py

@@ -371,11 +371,18 @@ def _check_keyword_parentheses(self, tokens: List[TokenInfo], start: int) -> Non
         if tokens[start + 1].string != "(":
             return
         found_and_or = False
+        contains_walrus_operator = False
+        walrus_operator_depth = 0
         depth = 0
         keyword_token = str(tokens[start].string)
         line_num = tokens[start].start[0]
         for i in range(start, len(tokens) - 1):
             token = tokens[i]
+
+            if token.string == ":=":
+                contains_walrus_operator = True
+                walrus_operator_depth = depth
+
             # If we hit a newline, then assume any parens were for continuation.
             if token.type == tokenize.NL:
                 return
@@ -390,6 +397,11 @@ def _check_keyword_parentheses(self, tokens: List[TokenInfo], start: int) -> Non
                         tokens[i + 1].type in
                          (tokenize.NEWLINE, tokenize.ENDMARKER, tokenize.COMMENT)):
                     # The empty tuple () is always accepted.
+                    if contains_walrus_operator and walrus_operator_depth - 1 == depth:
+                        # Reset variable for possible following expressions
+                        contains_walrus_operator = False
+                        walrus_operator_depth = None
+                        continue
                     if i == start + 2:
                         return
                     if keyword_token == "not":

tests/checkers/unittest_format.py

@@ -184,6 +184,28 @@ def testCheckKeywordParensHandlesUnnecessaryParens(self):
             with self.assertAddsMessages(msg):
                 self.checker._check_keyword_parentheses(_tokenize_str(code), offset)
 
+    def testNoSuperfluousParensWalrusOperatorIf(self):
+        """Parenthesis change the meaning of assignment in the walrus operator
+        and so are not superfluous:"""
+        code = "[odd for i in range(99) if (odd := is_odd(i))]"
+        offset = 0
+        with self.assertNoMessages():
+            self.checker._check_keyword_parentheses(_tokenize_str(code), offset)
+
+    def testPositiveSuperfluousParensWalrusOperatorIf(self):
+        """Test positive superfluous parens with the walrus operator"""
+        code = "[odd for i in range(99) if ((odd := is_odd(i)))]"
+        offset = 0
+        msg = Message("superfluous-parens", line=1, args="if")
+        with self.assertAddsMessages(msg):
+            self.checker._check_keyword_parentheses(_tokenize_str(code), 0)
+
+    def testSuperfluousParensWalrusOperatorNot(self):
+        """Test superfluous-parens with the not operator"""
+        code = "not (foo := 5)"
+        with self.assertNoMessages():
+            self.checker._check_keyword_parentheses(_tokenize_str(code), 0)
+
     def testCheckIfArgsAreNotUnicode(self):
         cases = [("if (foo):", 0), ("assert (1 == 1)", 0)]