SONARPY-638 Fix S5720 false positive on Enum._generate_next_value_ (#929)

Co-authored-by: Vibe Bot <vibe-bot@sonarsource.com>
GitOrigin-RevId: fe66b00074a56902d8c633f3bb531d1d79b83e8b

Author: 2 people

python-checks/src/main/java/org/sonar/python/checks/InstanceMethodSelfAsFirstCheck.java

@@ -93,6 +93,11 @@ private boolean isRelevantMethod(ClassDef classDef, ClassSymbol classSymbol, Fun
       return false;
     }
 
+    // Skip _generate_next_value_ in Enum subclasses: it is a static protocol method per the Python docs
+    if ("_generate_next_value_".equals(functionDef.name().name()) && classSymbol.isOrExtends("enum.Enum")) {
+      return false;
+    }
+
     // Skip if the class has a ignored decorator
     if (functionDef.decorators().stream().anyMatch(this::isNonInstanceMethodDecorator)) {
       return false;

python-checks/src/test/resources/checks/instanceMethodSelfAsFirst.py

@@ -182,3 +182,39 @@ def used_as_decorator_call(method):  # OK
 
 @used_as_decorator_call()
 def decorated(self): ...
+
+from enum import Enum, auto
+import enum
+
+# Do not raise on _generate_next_value_ in Enum subclasses
+class MyAutoName(Enum):
+    def _generate_next_value_(name, start, count, last_values):  # OK
+        return name
+
+class Animal(Enum):
+    def _generate_next_value_(name, start, count, last_values):  # OK
+        return name.lower()
+
+    DOG = auto()
+    CAT = auto()
+
+class UpperCaseEnum(enum.Enum):
+    def _generate_next_value_(name, start, count, last_values):  # OK
+        return name.upper()
+
+class NotAnEnum:
+    def _generate_next_value_(name, start, count, last_values):  # Noncompliant
+        return name
+
+class EnumWithOtherMethod(Enum):
+    def regular_method(arg):  # Noncompliant
+        pass
+
+# Indirect Enum subclass: _generate_next_value_ should also be exempt
+class BaseAutoEnum(Enum):
+    def _generate_next_value_(name, start, count, last_values):  # OK
+        return name.upper()
+
+class DerivedAutoEnum(BaseAutoEnum):
+    def _generate_next_value_(name, start, count, last_values):  # OK
+        return name.lower()