C#: Add test case for indexer calls and update test expected for other files.

Author: michaelnebel

csharp/ql/test/library-tests/indexers/Indexers13.expected

@@ -0,0 +1,3 @@
+| indexers.cs:24:21:24:24 | Item | indexers.cs:62:22:62:29 | access to indexer | indexers.cs:26:13:26:15 | get_Item |
+| indexers.cs:24:21:24:24 | Item | indexers.cs:65:25:65:32 | access to indexer | indexers.cs:34:13:34:15 | set_Item |
+| indexers.cs:143:24:143:27 | Item | indexers.cs:157:21:157:24 | access to indexer | indexers.cs:145:13:145:15 | get_Item |

csharp/ql/test/library-tests/indexers/Indexers13.ql

@@ -0,0 +1,8 @@
+import csharp
+
+from IndexerCall ic, Indexer i, Accessor target
+where
+  ic.getIndexer() = i and
+  ic.getTarget() = target and
+  i.fromSource()
+select i, ic, target

csharp/ql/test/library-tests/indexers/PrintAst.expected

@@ -360,3 +360,57 @@ indexers.cs:
 #  130|         4: [BlockStmt] {...}
 #  130|           0: [ReturnStmt] return ...;
 #  130|             0: [IntLiteral] 0
+#  134|   5: [RefStruct] S
+#  136|     6: [Field] x
+#  136|       -1: [TypeMention] int
+#  138|     7: [InstanceConstructor] S
+#-----|       2: (Parameters)
+#  138|         0: [Parameter] v
+#  138|           -1: [TypeMention] int
+#  139|       4: [BlockStmt] {...}
+#  140|         0: [ExprStmt] ...;
+#  140|           0: [AssignExpr] ... = ...
+#  140|             0: [FieldAccess] access to field x
+#  140|             1: [RefExpr] ref ...
+#  140|               0: [ParameterAccess] access to parameter v
+#  143|     8: [Indexer] Item
+#  143|       -1: [TypeMention] int
+#-----|       1: (Parameters)
+#  143|         0: [Parameter] i
+#  143|           -1: [TypeMention] int
+#  145|       3: [Getter] get_Item
+#-----|         2: (Parameters)
+#  143|           0: [Parameter] i
+#  145|         4: [BlockStmt] {...}
+#  145|           0: [ReturnStmt] return ...;
+#  145|             0: [RefExpr] ref ...
+#  145|               0: [FieldAccess] access to field x
+#  149|   6: [Class] TestRefReturns
+#  151|     6: [Method] M
+#  151|       -1: [TypeMention] Void
+#  152|       4: [BlockStmt] {...}
+#  153|         0: [LocalVariableDeclStmt] ... ...;
+#  153|           0: [LocalVariableDeclAndInitExpr] Int32 a = ...
+#  153|             -1: [TypeMention] int
+#  153|             0: [LocalVariableAccess] access to local variable a
+#  153|             1: [IntLiteral] 0
+#  155|         1: [LocalVariableDeclStmt] ... ...;
+#  155|           0: [LocalVariableDeclAndInitExpr] S s = ...
+#  155|             -1: [TypeMention] S
+#  155|             0: [LocalVariableAccess] access to local variable s
+#  155|             1: [ObjectCreation] object creation of type S
+#  155|               -1: [TypeMention] S
+#  155|               0: [LocalVariableAccess] access to local variable a
+#  156|         2: [ExprStmt] ...;
+#  156|           0: [AssignExpr] ... = ...
+#  156|             0: [IndexerCall] access to indexer
+#  156|               -1: [LocalVariableAccess] access to local variable s
+#  156|               0: [IntLiteral] 0
+#  156|             1: [IntLiteral] 1
+#  157|         3: [LocalVariableDeclStmt] ... ...;
+#  157|           0: [LocalVariableDeclAndInitExpr] Int32 x = ...
+#  157|             -1: [TypeMention] int
+#  157|             0: [LocalVariableAccess] access to local variable x
+#  157|             1: [IndexerCall] access to indexer
+#  157|               -1: [LocalVariableAccess] access to local variable s
+#  157|               0: [IntLiteral] 0

csharp/ql/test/library-tests/indexers/indexers.cs

@@ -130,4 +130,31 @@ public bool this[int index]
             get { return 0; }
         }
     }
+
+    public ref struct S
+    {
+        private ref int x;
+
+        public S(ref int v)
+        {
+            x = ref v;
+        }
+
+        public ref int this[int i]
+        {
+            get { return ref x; }
+        }
+    }
+
+    public class TestRefReturns
+    {
+        public void M()
+        {
+            int a = 0;
+
+            S s = new S(ref a);
+            s[0] = 1;
+            var x = s[0];
+        }
+    }
 }