C#: Update cs/static/field-written-by-instance to handle properties.

Author: michaelnebel

csharp/ql/src/Likely Bugs/StaticFieldWrittenByInstance.ql

@@ -1,6 +1,6 @@
 /**
  * @name Static field written by instance method
- * @description Finds instance methods that write static fields.
+ * @description Finds instance methods and properties that write to static fields.
  *              This is tricky to get right if multiple instances are being manipulated,
  *              and generally bad practice.
  * @kind problem
@@ -14,12 +14,12 @@
 
 import csharp
 
-from FieldWrite fw, Field f, Callable m
+from FieldWrite fw, Field f, Callable c
 where
   fw.getTarget() = f and
   f.isStatic() and
-  m = fw.getEnclosingCallable() and
-  not m.(Member).isStatic() and
-  f.getDeclaringType() = m.getDeclaringType() and
-  m.fromSource()
-select fw.(VariableAccess), "Write to static field from instance method or constructor."
+  c = fw.getEnclosingCallable() and
+  not exists(Member m | m = c or m = c.(Accessor).getDeclaration() | m.isStatic()) and
+  f.getDeclaringType() = c.getDeclaringType() and
+  c.fromSource()
+select fw.(VariableAccess), "Write to static field from instance method, property or constructor."