Merge pull request #20142 from joefarebrother/python-qual-subclass-shadow

Python: Modernise Superclass attribute shadows subclass method query

python/ql/test/query-tests/Classes/subclass-shadowing/SubclassShadowing.expected

@@ -1 +1,2 @@
-| subclass_shadowing.py:10:5:10:21 | FunctionExpr | Method shadow is shadowed by an $@ in super class 'Base'. | subclass_shadowing.py:6:9:6:23 | AssignStmt | attribute |
+| subclass_shadowing.py:11:5:11:21 | Function shadow | This method is shadowed by $@ in superclass $@. | subclass_shadowing.py:7:9:7:19 | ControlFlowNode for Attribute | attribute shadow | subclass_shadowing.py:4:1:4:11 | Class Base | Base |
+| subclass_shadowing.py:41:5:41:18 | Function foo | This method is shadowed by $@ in superclass $@. (read-only property may cause an error if written to in the superclass) | subclass_shadowing.py:35:9:35:16 | ControlFlowNode for Attribute | attribute foo | subclass_shadowing.py:33:1:33:12 | Class Base3 | Base3 |

python/ql/test/query-tests/Classes/subclass-shadowing/SubclassShadowing.qlref

@@ -1 +1,2 @@
-Classes/SubclassShadowing.ql
+query: Classes/SubclassShadowing/SubclassShadowing.ql
+postprocess: utils/test/InlineExpectationsTestQuery.ql

python/ql/test/query-tests/Classes/subclass-shadowing/subclass_shadowing.py

@@ -1,30 +1,51 @@
 #Subclass shadowing
 
-class Base(object):
+# BAD: `shadow` method shadows attribute
+class Base:
 
     def __init__(self):
         self.shadow = 4
 
 class Derived(Base):
 
-    def shadow(self):
+    def shadow(self): # $ Alert 
         pass
     
     
-#OK if the super class defines the method as well.
-#Since the original method must exist for some reason.
-#See JSONEncoder.default for real example
+# OK: Allow if superclass also shadows its own method, as this is likely intended.
+# Example: stdlib JSONEncoder.default uses this pattern.  
+class Base2:
 
-class Base2(object):
+    def __init__(self, default=None):
+        if default:
+            self.default = default
 
-    def __init__(self, shadowy=None):
-        if shadowy:
-            self.shadow = shadowy
-
-    def shadow(self):
+    def default(self):
         pass
 
 class Derived2(Base2):
 
-    def shadow(self):
+    def default(self): # No alert
         return 0
+
+# Properties 
+
+class Base3:
+    def __init__(self):
+        self.foo = 1 
+        self.bar = 2 
+
+class Derived3(Base3):
+    # BAD: Write to foo in superclass init raises an error.
+    @property 
+    def foo(self): # $ Alert
+        return 2 
+    
+    # OK: This property has a setter, so the write is OK.
+    @property 
+    def bar(self): # No alert
+        return self._bar 
+    
+    @bar.setter 
+    def bar(self, val):
+        self._bar = val