unions (untagged)

compiler/lexer/lexer.odin

@@ -18,6 +18,7 @@ keyword_kind :: proc(text: string) -> token.Kind {
 	case "c_func":        return .Keyword_C_Func
 	case "struct":        return .Keyword_Struct
 	case "c_struct":      return .Keyword_C_Struct
+	case "union":         return .Keyword_Union
 	case "enum":          return .Keyword_Enum
 	case "distinct":      return .Keyword_Distinct
 	case "alias":         return .Keyword_Alias

compiler/parser/parser.odin

@@ -1727,16 +1727,19 @@ parse_function :: proc(parser: ^Parser, name: token.Token, c_abi: bool) {
 	})
 }
 
-parse_struct :: proc(parser: ^Parser, name: token.Token, c_layout: bool) {
+parse_struct :: proc(parser: ^Parser, name: token.Token, c_layout: bool, is_union := false) {
 	start := advance(parser)
 	id := types.named(&parser.module.type_store, u32(parser.pkg), u32(name.symbol))
 	ended_by_newline := current(parser).kind == .Newline
 	skip_newlines(parser)
 	if current(parser).kind != .Left_Brace {
 		if !c_layout {
-			source.add(parser.diagnostics, start.span, "native struct declarations require a body")
+			source.add(
+				parser.diagnostics, start.span,
+				"native union declarations require a body" if is_union else "native struct declarations require a body",
+			)
 		}
-		if !types.define_struct(&parser.module.type_store, id, nil, c_layout, true) {
+		if !types.define_record(&parser.module.type_store, id, nil, c_layout, true, is_union) {
 			source.addf(parser.diagnostics, name.span, "duplicate type declaration '%s'", token_text(parser, name))
 		}
 		if !ended_by_newline {
@@ -1772,7 +1775,7 @@ parse_struct :: proc(parser: ^Parser, name: token.Token, c_layout: bool) {
 	if _, ok := allow(parser, .Right_Brace); !ok {
 		source.add(parser.diagnostics, current(parser).span, "expected '}' after struct fields")
 	}
-	if !types.define_struct(&parser.module.type_store, id, fields[:], c_layout, false) {
+	if !types.define_record(&parser.module.type_store, id, fields[:], c_layout, false, is_union) {
 		source.addf(parser.diagnostics, name.span, "duplicate type declaration '%s'", token_text(parser, name))
 	}
 	_ = finish_statement(parser)
@@ -2054,6 +2057,10 @@ parse_top_level :: proc(parser: ^Parser) {
 		parse_struct(parser, name, current(parser).kind == .Keyword_C_Struct)
 		return
 	}
+	if operator.kind == .Colon_Colon && current(parser).kind == .Keyword_Union {
+		parse_struct(parser, name, false, is_union=true)
+		return
+	}
 	if operator.kind == .Colon_Colon && current(parser).kind == .Keyword_Enum {
 		parse_enum(parser, name)
 		return

compiler/token/token.odin

@@ -53,6 +53,7 @@ Kind :: enum u8 {
 	Keyword_C_Func,
 	Keyword_Struct,
 	Keyword_C_Struct,
+	Keyword_Union,
 	Keyword_Enum,
 	Keyword_Distinct,
 	Keyword_Alias,