[vala/wip/issue548: 2/2] WIP vala: Allow explicit interface methods to be virtual

[Rico Tzschichholz <ricotz src gnome org>]

commit c4729b026be57e39f88dfdbfe0db638a9b6b1a35
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Sat Dec 1 15:27:08 2018 +0100

    WIP vala: Allow explicit interface methods to be virtual

 tests/Makefile.am                              |  1 +
 tests/objects/classes-interfaces-virtuals.vala | 34 ++++++++++++++++++++++++++
 vala/valaclass.vala                            | 12 ++++++++-
 3 files changed, 46 insertions(+), 1 deletion(-)
---
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 15cefa931..442431592 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -253,6 +253,7 @@ TESTS = \
        objects/chainup.vala \
        objects/classes.vala \
        objects/classes-interfaces.vala \
+       objects/classes-interfaces-virtuals.vala \
        objects/compact-class.vala \
        objects/compact-class-destructor.vala \
        objects/constructor-variadic.test \
diff --git a/tests/objects/classes-interfaces-virtuals.vala b/tests/objects/classes-interfaces-virtuals.vala
new file mode 100644
index 000000000..cf56c62b7
--- /dev/null
+++ b/tests/objects/classes-interfaces-virtuals.vala
@@ -0,0 +1,34 @@
+interface IFoo : Object {
+       public abstract int foo ();
+}
+
+interface IBar : Object {
+       public abstract string foo ();
+}
+
+class Foo : Object, IFoo, IBar {
+       public virtual int IFoo.foo () {
+               return 42;
+       }
+       public string IBar.foo () {
+               return "foo";
+       }
+}
+
+class Bar : Foo {
+       public override int foo () {
+               return 23;
+       }
+}
+
+void main () {
+       var foo = new Foo ();
+       assert (foo.foo () == 42);
+       assert (((IBar) foo).foo () == "foo");
+
+       var bar = new Bar ();
+       assert (bar.foo () == 23);
+       assert (((Foo) bar).foo () == 23);
+       assert (((IFoo) bar).foo () == 23);
+       assert (((IBar) bar).foo () == "foo");
+}
diff --git a/vala/valaclass.vala b/vala/valaclass.vala
index 2be6b2e75..aa206cd34 100644
--- a/vala/valaclass.vala
+++ b/vala/valaclass.vala
@@ -297,11 +297,21 @@ public class Vala.Class : ObjectTypeSymbol {
                        }
                }
 
+               Symbol? sym = null;
+               if (m.base_interface_type != null && !(m.is_abstract || m.is_virtual)) {
+                       sym = scope.lookup (m.name);
+                       if (sym != null) {
+                               scope.remove (m.name);
+                       }
+               }
                base.add_method (m);
                // explicit interface method implementation
-               if (m.base_interface_type != null) {
+               if (m.base_interface_type != null && !(m.is_abstract || m.is_virtual)) {
                        scope.remove (m.name);
                        scope.add (null, m);
+                       if (sym != null) {
+                               scope.add (m.name, sym);
+                       }
                }
        }