ast: support attributes for `ast.SumType` (#13010)

vlib/v/ast/ast.v

@@ -1092,6 +1092,7 @@ pub:
 	comments      []Comment
 	typ           Type
 	generic_types []Type
+	attrs         []Attr // attributes of type declaration
 pub mut:
 	variants []TypeNode
 }

vlib/v/fmt/fmt.v

@@ -1293,6 +1293,7 @@ pub fn (mut f Fmt) fn_type_decl(node ast.FnTypeDecl) {
 }
 
 pub fn (mut f Fmt) sum_type_decl(node ast.SumTypeDecl) {
+	f.attrs(node.attrs)
 	start_pos := f.out.len
 	if node.is_pub {
 		f.write('pub ')

vlib/v/fmt/tests/sum_attributes_keep.vv

@@ -0,0 +1,14 @@
+[derive: 'DeserBincode,SerBincode']
+type OneOf = ItemA | ItemB
+
+[derive: 'DeserBincode,SerBincode']
+struct ItemA {
+	a string
+}
+
+[derive: 'DeserBincode,SerBincode']
+struct ItemB {
+	b   int
+	bb  u64
+	bbb string
+}

vlib/v/parser/parser.v

@@ -3465,6 +3465,7 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 			is_pub: is_pub
 			variants: sum_variants
 			generic_types: generic_types
+			attrs: p.attrs
 			pos: decl_pos
 			comments: comments
 		}