Merge pull request github#18508 from michaelnebel/csharp/implicitinheritedtostring

C#: Also syntheize calls to inherited `ToString`.

Author: michaelnebel

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/ImplicitToString.cs

@@ -14,14 +14,21 @@ internal sealed class ImplicitToString : Expression
         /// </summary>
         private static IMethodSymbol? GetToStringMethod(ITypeSymbol? type)
         {
-            return type?
+            if (type is null)
+            {
+                return null;
+            }
+
+            var toString = type
                 .GetMembers()
                 .OfType<IMethodSymbol>()
                 .Where(method =>
                     method.GetName() == "ToString" &&
                     method.Parameters.Length == 0
                 )
                 .FirstOrDefault();
+
+            return toString ?? GetToStringMethod(type.BaseType);
         }
 
         private ImplicitToString(ExpressionNodeInfo info, IMethodSymbol toString) : base(new ExpressionInfo(info.Context, AnnotatedTypeSymbol.CreateNotAnnotated(toString.ReturnType), info.Location, ExprKind.METHOD_INVOCATION, info.Parent, info.Child, isCompilerGenerated: true, info.ExprValue))

csharp/ql/test/library-tests/implicittostring/implicitToString.cs

@@ -10,6 +10,10 @@ public override string ToString()
         }
     }
 
+    public class Container2 : Container { }
+
+    public class Container3 { }
+
     public class FormattableContainer : IFormattable
     {
         public string ToString(string format, IFormatProvider formatProvider)
@@ -40,5 +44,11 @@ public void M()
         y = "Hello" + formattableContainer; // Implicit call to ToString().
         y = $"Hello {formattableContainer}"; // Implicit call to ToString(string, IFormatProvider). We don't handle this.
         y = $"Hello {formattableContainer:D}"; // Implicit call to ToString(string, IFormatProvider). We don't handle this.
+
+        var container2 = new Container2();
+        y = "Hello" + container2; // Implicit Container.ToString call.
+
+        var container3 = new Container3();
+        y = "Hello" + container3; // Implicit Object.ToString call.
     }
 }

csharp/ql/test/library-tests/implicittostring/implicitToString.expected

@@ -1,4 +1,6 @@
-| implicitToString.cs:31:27:31:35 | call to method ToString |
-| implicitToString.cs:33:22:33:30 | call to method ToString |
-| implicitToString.cs:35:22:35:30 | call to method ToString |
-| implicitToString.cs:40:23:40:42 | call to method ToString |
+| implicitToString.cs:35:27:35:35 | call to method ToString | Container |
+| implicitToString.cs:37:22:37:30 | call to method ToString | Container |
+| implicitToString.cs:39:22:39:30 | call to method ToString | Container |
+| implicitToString.cs:44:23:44:42 | call to method ToString | FormattableContainer |
+| implicitToString.cs:49:23:49:32 | call to method ToString | Container |
+| implicitToString.cs:52:23:52:32 | call to method ToString | Object |

csharp/ql/test/library-tests/implicittostring/implicitToString.ql

@@ -2,4 +2,4 @@ import csharp
 
 from MethodCall c
 where c.isImplicit()
-select c
+select c, c.getTarget().getDeclaringType().toString()

csharp/ql/test/query-tests/Nullness/Implications.expected

@@ -908,8 +908,8 @@
 | D.cs:253:13:253:14 | access to local variable o2 | null | D.cs:249:18:249:38 | ... ? ... : ... | null |
 | D.cs:266:13:266:27 | ... is ... | true | D.cs:266:13:266:17 | access to local variable other | non-null |
 | D.cs:310:21:310:26 | ... + ... | non-null | D.cs:310:21:310:22 | "" | non-null |
-| D.cs:310:21:310:26 | ... + ... | non-null | D.cs:310:26:310:26 | access to parameter a | non-null |
-| D.cs:310:21:310:26 | ... + ... | null | D.cs:310:26:310:26 | access to parameter a | null |
+| D.cs:310:21:310:26 | ... + ... | non-null | D.cs:310:26:310:26 | call to method ToString | non-null |
+| D.cs:310:21:310:26 | ... + ... | null | D.cs:310:26:310:26 | call to method ToString | null |
 | D.cs:312:17:312:23 | !... | false | D.cs:312:18:312:23 | access to local variable s_null | true |
 | D.cs:312:17:312:23 | !... | true | D.cs:312:18:312:23 | access to local variable s_null | false |
 | D.cs:318:16:318:62 | ... && ... | true | D.cs:318:16:318:36 | ... == ... | true |