C#: Fix FPs in RedundantToStringCall.ql

Author: hvitved

csharp/ql/lib/semmle/code/csharp/commons/Strings.qll

@@ -29,7 +29,7 @@ class ImplicitToStringExpr extends Expr {
       m = p.getCallable()
     |
       m = any(SystemTextStringBuilderClass c).getAMethod() and
-      m.getName().regexpMatch("Append(Line)?") and
+      m.getName() = "Append" and
       not p.getType() instanceof ArrayType
       or
       p instanceof StringFormatItemParameter and

csharp/ql/src/Useless code/RedundantToStringCall.ql

@@ -18,5 +18,6 @@ import semmle.code.csharp.frameworks.System
 from MethodCall mc
 where
   mc instanceof ImplicitToStringExpr and
-  mc.getTarget() instanceof ToStringMethod
+  mc.getTarget() instanceof ToStringMethod and
+  not mc.getQualifier() instanceof BaseAccess
 select mc, "Redundant call to 'ToString' on a String object."

csharp/ql/test/query-tests/Useless Code/RedundantToStringCall/RedundantToStringCall.cs

@@ -17,8 +17,8 @@ public void M(object o)
         var sb = new StringBuilder();
         sb.Append(o.ToString()); // $ Alert
         sb.Append(o); // GOOD
-        sb.AppendLine(o.ToString()); // $ SPURIOUS: Alert
+        sb.AppendLine(o.ToString()); // GOOD
 
-        Console.WriteLine($"Hello: {base.ToString()}"); // $ SPURIOUS: Alert
+        Console.WriteLine($"Hello: {base.ToString()}"); // GOOD
     }
 }

csharp/ql/test/query-tests/Useless Code/RedundantToStringCall/RedundantToStringCall.expected

@@ -2,6 +2,4 @@
 | RedundantToStringCall.cs:11:37:11:48 | call to method ToString | Redundant call to 'ToString' on a String object. |
 | RedundantToStringCall.cs:14:39:14:50 | call to method ToString | Redundant call to 'ToString' on a String object. |
 | RedundantToStringCall.cs:18:19:18:30 | call to method ToString | Redundant call to 'ToString' on a String object. |
-| RedundantToStringCall.cs:20:23:20:34 | call to method ToString | Redundant call to 'ToString' on a String object. |
-| RedundantToStringCall.cs:22:37:22:51 | call to method ToString | Redundant call to 'ToString' on a String object. |
 | RedundantToStringCallBad.cs:7:45:7:56 | call to method ToString | Redundant call to 'ToString' on a String object. |