C#: Address review comment

  - Flow from expressions with a value is excluded.

Author: calumgrant

csharp/ql/src/Security Features/CWE-020/RuntimeChecksBypass.ql

@@ -35,7 +35,9 @@ Expr uncheckedWrite(Callable callable, Field f) {
   result.getEnclosingCallable() = callable and
   not callable.calls*(checkedWrite(f, _, _).getEnclosingCallable()) and
   // Exclude object creations because they were not deserialized
-  not exists(ObjectCreation src | DataFlow::localExprFlow(src, result))
+  not exists(Expr src | DataFlow::localExprFlow(src, result) |
+    src instanceof ObjectCreation or src.hasValue()
+  )
 }
 
 from BinarySerializableType t, Field f, IfStmt check, Expr write, Expr unsafeWrite

csharp/ql/test/query-tests/Security Features/CWE-020/RuntimeChecksBypass.cs

@@ -17,7 +17,7 @@ public Test1(string v)
     [OnDeserializing]
     public void Deserialize()
     {
-        f = "invalid";  // BAD
+        f = $"invalid";  // BAD
     }
 }
 
@@ -37,7 +37,7 @@ public Test2(string v)
     [OnDeserializing]
     public void Deserialize()
     {
-        var v = "invalid";
+        var v = $"invalid";
         f = v;  // BAD: False negative
 
         if (v == "valid")
@@ -63,7 +63,7 @@ public Test3(string v)
     [OnDeserializing]
     public void Deserialize()
     {
-        var v = "invalid";
+        var v = $"invalid";
         f = v;  // GOOD: False negative
         Assign(v);
     }
@@ -95,7 +95,7 @@ public Test4(string v)
     [OnDeserializing]
     public void Deserialize()
     {
-        var v = "invalid";
+        var v = $"invalid";
         if (v == "valid")
             Assign(v);
     }

csharp/ql/test/query-tests/Security Features/CWE-020/RuntimeChecksbypass.expected

@@ -1,4 +1,4 @@
-| RuntimeChecksBypass.cs:20:13:20:21 | "invalid" | This write to $@ may be circumventing a $@. | RuntimeChecksBypass.cs:7:19:7:19 | f | f | RuntimeChecksBypass.cs:11:9:14:9 | if (...) ... | check |
+| RuntimeChecksBypass.cs:20:13:20:22 | $"..." | This write to $@ may be circumventing a $@. | RuntimeChecksBypass.cs:7:19:7:19 | f | f | RuntimeChecksBypass.cs:11:9:14:9 | if (...) ... | check |
 | RuntimeChecksBypass.cs:124:15:124:34 | call to method GetInt32 | This write to $@ may be circumventing a $@. | RuntimeChecksBypass.cs:112:16:112:18 | Age | Age | RuntimeChecksBypass.cs:116:9:117:53 | if (...) ... | check |
 | RuntimeChecksBypass.cs:168:15:168:17 | access to local variable age | This write to $@ may be circumventing a $@. | RuntimeChecksBypass.cs:153:16:153:18 | Age | Age | RuntimeChecksBypass.cs:157:9:158:53 | if (...) ... | check |
 | RuntimeChecksBypassBad.cs:19:15:19:34 | call to method GetInt32 | This write to $@ may be circumventing a $@. | RuntimeChecksBypassBad.cs:7:16:7:18 | Age | Age | RuntimeChecksBypassBad.cs:11:9:12:53 | if (...) ... | check |