Merge pull request #4627 from tamasvajk/feature/csharp9-covariant-return

C#: Add test for covariant return types

csharp/ql/test/library-tests/csharp9/CovariantReturn.cs

@@ -0,0 +1,9 @@
+class A
+{
+    public virtual A M1() { throw null; }
+}
+
+class B : A
+{
+    public override B M1() { throw null; }
+}

csharp/ql/test/library-tests/csharp9/PrintAst.expected

@@ -117,6 +117,21 @@ BinaryPattern.cs:
 #   19|           1: [SwitchCaseExpr] ... => ...
 #   19|             0: [DiscardPatternExpr] _
 #   19|             2: [StringLiteral] "other"
+CovariantReturn.cs:
+#    1| [Class] A
+#    3|   5: [Method] M1
+#    3|     -1: [TypeMention] A
+#    3|     4: [BlockStmt] {...}
+#    3|       0: [ThrowStmt] throw ...;
+#    3|         0: [NullLiteral] null
+#    6| [Class] B
+#-----|   3: (Base types)
+#    6|     0: [TypeMention] A
+#    8|   5: [Method] M1
+#    8|     -1: [TypeMention] B
+#    8|     4: [BlockStmt] {...}
+#    8|       0: [ThrowStmt] throw ...;
+#    8|         0: [NullLiteral] null
 Discard.cs:
 #    3| [Class] Discard
 #    5|   5: [Method] M1

csharp/ql/test/library-tests/csharp9/covariantReturn.expected

@@ -0,0 +1 @@
+| A.M1 | A | B.M1 | B |

csharp/ql/test/library-tests/csharp9/covariantReturn.ql

@@ -0,0 +1,8 @@
+import csharp
+
+from Method m, Method overrider
+where
+  m.getAnOverrider() = overrider and
+  m.getFile().getStem() = "CovariantReturn"
+select m.getQualifiedName(), m.getReturnType().toString(), overrider.getQualifiedName(),
+  overrider.getReturnType().toString()