Merge pull request #2773 from hvitved/csharp/useless-assignment-to-local-default

C#: Remove false positives for `cs/useless-assignment-to-local`

csharp/ql/src/Dead Code/DeadStoreOfLocal.ql

@@ -114,7 +114,7 @@ class RelevantDefinition extends AssignableDefinition {
    */
   private predicate isDefaultLikeInitializer() {
     this.isInitializer() and
-    exists(Expr e | e = this.getSource() |
+    exists(Expr e | e = this.getSource().stripCasts() |
       exists(string val | val = e.getValue() |
         val = "0" or
         val = "-1" or

csharp/ql/test/query-tests/Dead Code/DeadStoreOfLocal/DeadStoreOfLocal.cs

@@ -389,6 +389,20 @@ class Initializers
             return s;
         return null;
     }
+
+    string M8()
+    {
+        string s = default; // "GOOD"
+        s = "";
+        return s;
+    }
+
+    string M9()
+    {
+        var s = (string)null; // "GOOD"
+        s = "";
+        return s;
+    }
 }
 
 class Anonymous