checker: fix printing interface variable in smartcast

vlib/context/empty_test.v

@@ -2,15 +2,15 @@ module context
 
 fn test_background() {
 	ctx := background()
-	assert '&context.Background' == ctx.str()
+	assert 'context.Background' == ctx.str()
 	if _ := ctx.value('') {
 		panic('This should never happen')
 	}
 }
 
 fn test_todo() {
 	ctx := todo()
-	assert '&context.TODO' == ctx.str()
+	assert 'context.TODO' == ctx.str()
 	if _ := ctx.value('') {
 		panic('This should never happen')
 	}

vlib/v/checker/checker.v

@@ -1441,7 +1441,10 @@ fn (mut c Checker) selector_expr(mut node ast.SelectorExpr) ast.Type {
 	if node.expr.is_auto_deref_var() {
 		if mut node.expr is ast.Ident {
 			if mut node.expr.obj is ast.Var {
-				typ = node.expr.obj.typ
+				if node.expr.obj.orig_type == 0 || (node.expr.obj.orig_type != 0
+					&& c.table.sym(node.expr.obj.orig_type).kind != .interface_) {
+					typ = node.expr.obj.typ
+				}
 			}
 		}
 	}
@@ -3798,6 +3801,7 @@ fn (mut c Checker) smartcast(mut expr ast.Expr, cur_type ast.Type, to_type_ ast.
 					is_used: true
 					is_mut: expr.is_mut
 					is_inherited: is_inherited
+					is_auto_deref: sym.kind == .interface_
 					smartcasts: smartcasts
 					orig_type: orig_type
 				})

vlib/v/tests/empty_interface_test.v

@@ -10,5 +10,5 @@ fn print_out(x Any) string {
 
 fn test_empty_interface() {
 	ret := print_out('12345')
-	assert ret == '&12345'
+	assert ret == '12345'
 }

vlib/v/tests/print_interface_variable_in_smartcast_test.v

@@ -0,0 +1,25 @@
+interface Any {}
+
+fn do(v Any) string {
+	match v {
+		int {
+			println('> integer answer: ${2 * v}')
+			return '${2 * v}'
+		}
+		string {
+			println('> string answer: ${v}, len: ${v.len}')
+			return '${v}'
+		}
+		else {
+			return ''
+		}
+	}
+}
+
+fn test_printing_interface_variable_in_smartcast() {
+	s1 := do(123)
+	assert s1 == '246'
+
+	s2 := do('abc')
+	assert s2 == 'abc'
+}