checker/cgen: return interfaces

vlib/v/checker/checker.v

@@ -1232,6 +1232,10 @@ pub fn (mut c Checker) return_stmt(mut return_stmt ast.Return) {
 			if is_generic {
 				exp_typ_sym = c.table.get_type_symbol(c.cur_generic_type)
 			}
+			if exp_typ_sym.kind == .interface_ {
+				c.type_implements(got_typ, exp_type, return_stmt.pos)
+				continue
+			}
 			c.error('cannot use `$got_typ_sym.name` as type `$exp_typ_sym.name` in return argument',
 				pos)
 		}

vlib/v/gen/cgen.v

@@ -2300,7 +2300,7 @@ fn (mut g Gen) return_statement(node ast.Return) {
 		if fn_return_is_optional && !node.types[0].flag_is(.optional) && return_sym.name !=
 			'Option' {
 			styp := g.base_type(g.fn_decl.return_type)
-			g.write('/*:)$return_sym.name*/opt_ok(&($styp[]) { ')
+			g.write('/*$return_sym.name*/opt_ok(&($styp[]) { ')
 			if !g.fn_decl.return_type.is_ptr() && node.types[0].is_ptr() {
 				// Automatic Dereference for optional
 				g.write('*')
@@ -2314,7 +2314,13 @@ fn (mut g Gen) return_statement(node ast.Return) {
 			g.writeln(' }, sizeof($styp));')
 			return
 		}
+		if sym.kind == .interface_ {
+			g.interface_call(node.types[0], g.fn_decl.return_type)
+		}
 		g.expr_with_cast(node.exprs[0], node.types[0], g.fn_decl.return_type)
+		if sym.kind == .interface_ {
+			g.write(')')
+		}
 	}
 	g.writeln(';')
 }

vlib/v/tests/interface_test.v

@@ -238,3 +238,8 @@ fn foo2(a Animal) int {
 		return 0
 	}
 }
+
+fn new_animal() Animal {
+	dog := Dog{}
+	return dog
+}