v: fix -skip-unused error with aggregate method call

vlib/v/markused/walker.v

@@ -528,6 +528,17 @@ pub fn (mut w Walker) call_expr(mut node ast.CallExpr) {
 		}
 		return
 	}
+	if node.is_method && node.left_type != 0 {
+		left_sym := w.table.sym(node.left_type)
+		if left_sym.info is ast.Aggregate {
+			for types in left_sym.info.types {
+				fn_name := '${types.idx()}.${node.name}'
+				if !w.used_fns[fn_name] {
+					w.mark_aggregate_call_used(fn_name, types)
+				}
+			}
+		}
+	}
 	w.expr(node.left)
 	w.or_block(node.or_block)
 
@@ -566,6 +577,16 @@ pub fn (mut w Walker) call_expr(mut node ast.CallExpr) {
 	}
 }
 
+// visit aggregate type method declaration
+pub fn (mut w Walker) mark_aggregate_call_used(fn_name string, left_type ast.Type) {
+	if w.used_fns[fn_name] {
+		return
+	}
+	w.mark_fn_as_used(fn_name)
+	stmt := w.all_fns[fn_name] or { return }
+	w.stmts(stmt.stmts)
+}
+
 pub fn (mut w Walker) fn_by_name(fn_name string) {
 	if w.used_fns[fn_name] {
 		return

vlib/v/tests/skip_unused/aggregate_call.vv

@@ -0,0 +1,20 @@
+struct Foo {}
+
+struct Bar {}
+
+type SumType = Foo | Bar
+
+fn (f Foo) pstr() {
+}
+
+fn (b Bar) pstr() {
+}
+
+fn main() {
+	a := SumType(Foo{})
+	match a {
+		Foo, Bar {
+			a.pstr()
+		}
+	}
+}