SONARPY-4017 S8494 Fixing FPs on naming conventions (#1047)

GitOrigin-RevId: 4088afedaa3541b3d30fe804b95102aedd1f3a88

Author: joke1196

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

@@ -110,6 +110,7 @@ private static void checkClass(SubscriptionContext ctx) {
     }
 
     // Check each instance method
+    String className = classDef.name().name();
     for (FunctionDef functionDef : TreeUtils.topLevelFunctionDefs(classDef)) {
       PythonType funcType = functionDef.name().typeV2();
       if (!(funcType instanceof FunctionType ft) || !ft.isInstanceMethod()) {
@@ -118,7 +119,7 @@ private static void checkClass(SubscriptionContext ctx) {
       List<Parameter> params = TreeUtils.positionalParameters(functionDef);
       if (!params.isEmpty()) {
         String selfName = params.get(0).name().name();
-        SelfAttributeAssignmentVisitor visitor = new SelfAttributeAssignmentVisitor(selfName, allowedSlots, ctx);
+        SelfAttributeAssignmentVisitor visitor = new SelfAttributeAssignmentVisitor(selfName, allowedSlots, className, ctx);
         functionDef.body().accept(visitor);
       }
     }
@@ -298,11 +299,13 @@ private static boolean processParentClass(ClassDef parentClassDef, Set<String> a
   private static class SelfAttributeAssignmentVisitor extends BaseTreeVisitor {
     private final String selfName;
     private final Set<String> allowedSlots;
+    private final String className;
     private final SubscriptionContext ctx;
 
-    SelfAttributeAssignmentVisitor(String selfName, Set<String> allowedSlots, SubscriptionContext ctx) {
+    SelfAttributeAssignmentVisitor(String selfName, Set<String> allowedSlots, String className, SubscriptionContext ctx) {
       this.selfName = selfName;
       this.allowedSlots = allowedSlots;
+      this.className = className;
       this.ctx = ctx;
     }
 
@@ -346,9 +349,23 @@ private void checkQualifiedExpression(Expression expr) {
         return;
       }
       String attrName = qualifiedExpr.name().name();
-      if (!allowedSlots.contains(attrName)) {
+      if (!allowedSlots.contains(attrName) && !allowedSlots.contains(mangledName(attrName))) {
         ctx.addIssue(qualifiedExpr.name(), String.format(MESSAGE, attrName));
       }
     }
+
+    /**
+     * Returns the name-mangled form of a private attribute name within this class.
+     * Python mangles names starting with two underscores (but not ending with two underscores)
+     * by stripping leading underscores from the class name and prepending "_ClassName".
+     * For example, "__den" in class "_Rat" becomes "_Rat__den" (not "__Rat__den").
+     * See: https://docs.python.org/3/reference/expressions.html#atom-identifiers
+     */
+    private String mangledName(String attrName) {
+      if (attrName.startsWith("__") && !attrName.endsWith("__")) {
+        return "_" + className.replaceAll("^_+", "") + attrName;
+      }
+      return attrName;
+    }
   }
 }

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

@@ -802,3 +802,31 @@ class ConcatenatedSlots:
     def __init__(self):
         self.x = 1
         self.missing = 2  # FN: __slots__ is a binary expression, not a literal
+
+# Compliant: __slots__ uses mangled names and assignments use double-underscore syntax
+class Rat(object):
+    __slots__ = ['_Rat__num', '_Rat__den']
+
+    def __init__(self, num=0, den=1):
+        self.__num = num  # Compliant: stored as _Rat__num, which is in __slots__
+        self.__den = den  # Compliant: stored as _Rat__den, which is in __slots__
+
+
+# Issue raised when attribute is not in slots even with partial mangled entries
+class RatMissing(object):
+    __slots__ = ['_RatMissing__num']
+
+    def __init__(self, num=0, den=1):
+        self.__num = num  # Compliant: stored as _RatMissing__num, which is in __slots__
+        self.__den = den  # Noncompliant {{Add "__den" to the class's "__slots__".}}
+#            ^^^^^
+
+
+# Compliant: class name starts with underscore — mangling strips leading underscores from class name
+# Python mangles _Rat.__den to _Rat__den (not __Rat__den)
+class _Rat(object):
+    __slots__ = ['_Rat__num', '_Rat__den']
+
+    def __init__(self, num=0, den=1):
+        self.__num = num  # Compliant: stored as _Rat__num, which is in __slots__
+        self.__den = den  # Compliant: stored as _Rat__den, which is in __slots__