Allow undefined --- as a struct field default value.

src/check_expr.cpp

@@ -879,15 +879,20 @@ void check_record_field_decl(Checker *c, AstNode *decl, Array<Entity *> *fields,
 		e->identifier = name;
 
 		if (name_field_index < default_values.count) {
-			Operand op = default_values[name_field_index++];
-			check_init_variable(c, e, &op, str_lit("struct field assignment"));
-			if (is_operand_nil(op)) {
+			Operand a = default_values[name_field_index];
+			Operand b = default_values[name_field_index];
+			check_init_variable(c, e, &b, str_lit("struct field assignment"));
+			if (is_operand_nil(a)) {
 				e->Variable.default_is_nil = true;
-			} else if (op.mode != Addressing_Constant) {
-				error(op.expr, "Default field parameter must be a constant");
+			} else if (is_operand_undef(a)) {
+				e->Variable.default_is_undef = true;
+			} else if (b.mode != Addressing_Constant) {
+				error(b.expr, "Default field parameter must be a constant");
 			} else {
-				e->Variable.default_value = op.value;
+				e->Variable.default_value = b.value;
 			}
+
+			name_field_index++;
 		} else {
 			GB_ASSERT(type != nullptr);
 		}

src/checker.cpp

@@ -166,7 +166,9 @@ bool is_operand_value(Operand o) {
 bool is_operand_nil(Operand o) {
 	return o.mode == Addressing_Value && o.type == t_untyped_nil;
 }
-
+bool is_operand_undef(Operand o) {
+	return o.mode == Addressing_Value && o.type == t_untyped_undef;
+}
 
 struct BlockLabel {
 	String   name;

src/entity.cpp

@@ -87,6 +87,7 @@ struct Entity {
 			i32        field_src_index;
 			ExactValue default_value;
 			bool       default_is_nil;
+			bool       default_is_undef;
 			bool       default_is_location;
 			bool       is_immutable;
 			bool       is_thread_local;

src/ir.cpp

@@ -671,6 +671,8 @@ bool ir_type_has_default_values(Type *t) {
 					continue;
 				} else if (f->Variable.default_value.kind != ExactValue_Invalid) {
 					return true;
+				} else if (f->Variable.default_is_undef) {
+					return true;
 				}
 			}
 		}

src/ir_print.cpp

@@ -648,9 +648,14 @@ void ir_print_exact_value(irFileBuffer *f, irModule *m, ExactValue value, Type *
 
 			for (isize i = 0; i < value_count; i++) {
 				if (i > 0) ir_fprintf(f, ", ");
-				Type *elem_type = type->Record.fields[i]->type;
+				Entity *e = type->Record.fields[i];
 
-				ir_print_compound_element(f, m, values[i], elem_type);
+				if (!visited[i] && e->Variable.default_is_undef) {
+					ir_print_type(f, m, e->type);
+					ir_fprintf(f, " undef");
+				} else {
+					ir_print_compound_element(f, m, values[i], e->type);
+				}
 			}
 
 
@@ -682,12 +687,17 @@ void ir_print_exact_value(irFileBuffer *f, irModule *m, ExactValue value, Type *
 
 				for (isize i = 0; i < value_count; i++) {
 					if (i > 0) ir_fprintf(f, ", ");
-					Entity *field = type->Record.fields[i];
-					ExactValue value = {};
-					if (!field->Variable.default_is_nil) {
-						value = field->Variable.default_value;
+					Entity *e = type->Record.fields[i];
+					if (e->Variable.default_is_undef) {
+						ir_print_type(f, m, e->type);
+						ir_fprintf(f, " undef");
+					} else {
+						ExactValue value = {};
+						if (!e->Variable.default_is_nil) {
+							value = e->Variable.default_value;
+						}
+						ir_print_compound_element(f, m, value, e->type);
 					}
-					ir_print_compound_element(f, m, value, field->type);
 				}
 
 				ir_fprintf(f, "}");