all: _allow_multiple_values enum attribute (#5772)

vlib/v/ast/ast.v

@@ -623,12 +623,13 @@ pub:
 
 pub struct EnumDecl {
 pub:
-	name     string
-	is_pub   bool
-	is_flag  bool // true when the enum has [flag] tag
-	comments []Comment // enum Abc { /* comments */ ... }
-	fields   []EnumField
-	pos      token.Position
+	name             string
+	is_pub           bool
+	is_flag          bool // true when the enum has [flag] tag
+	is_multi_allowed bool
+	comments         []Comment // enum Abc { /* comments */ ... }
+	fields           []EnumField
+	pos              token.Position
 }
 
 pub struct AliasTypeDecl {

vlib/v/checker/checker.v

@@ -1467,7 +1467,7 @@ pub fn (mut c Checker) enum_decl(decl ast.EnumDecl) {
 					val := field_expr.val.i64()
 					if val < enum_min || val > enum_max {
 						c.error('enum value `$val` overflows int', field_expr.pos)
-					} else if int(val) in seen {
+					} else if !decl.is_multi_allowed && int(val) in seen {
 						c.error('enum value `$val` already exists', field_expr.pos)
 					}
 					seen << int(val)

vlib/v/gen/cgen.v

@@ -4120,7 +4120,14 @@ fn (mut g Gen) gen_str_for_enum(info table.Enum, styp, str_fn_name string) {
 	g.type_definitions.writeln('string ${str_fn_name}($styp it); // auto')
 	g.auto_str_funcs.writeln('string ${str_fn_name}($styp it) { /* gen_str_for_enum */')
 	g.auto_str_funcs.writeln('\tswitch(it) {')
+	// Only use the first multi value on the lookup
+	mut seen := []string{len:info.vals.len}
 	for val in info.vals {
+		if info.is_multi_allowed && val in seen {
+			continue
+		} else if info.is_multi_allowed {
+			seen << val
+		}
 		g.auto_str_funcs.writeln('\t\tcase ${s}_$val: return tos_lit("$val");')
 	}
 	g.auto_str_funcs.writeln('\t\tdefault: return tos_lit("unknown enum value");')

vlib/v/parser/parser.v

@@ -1503,6 +1503,7 @@ fn (mut p Parser) enum_decl() ast.EnumDecl {
 	p.top_level_statement_end()
 	p.check(.rcbr)
 	is_flag := 'flag' in p.attrs
+	is_multi_allowed := '_allow_multiple_values' in p.attrs
 	if is_flag {
 		if fields.len > 32 {
 			p.error('when an enum is used as bit field, it must have a max of 32 fields')
@@ -1524,12 +1525,14 @@ $pubfn (mut e  $enum_name) toggle(flag $enum_name)   { unsafe{ *e = int(*e) ^  (
 		info: table.Enum{
 			vals: vals
 			is_flag: is_flag
+			is_multi_allowed: is_multi_allowed
 		}
 	})
 	return ast.EnumDecl{
 		name: name
 		is_pub: is_pub
 		is_flag: is_flag
+		is_multi_allowed: is_multi_allowed
 		fields: fields
 		pos: start_pos.extend(end_pos)
 		comments: enum_decl_comments

vlib/v/table/atypes.v

@@ -683,6 +683,7 @@ pub struct Enum {
 pub:
 	vals    []string
 	is_flag bool
+	is_multi_allowed bool
 }
 
 pub struct Alias {