lowerAstErrors

fn lowerAstErrors(zg: *ZonGen) Allocator.Error!void {
    const gpa = zg.gpa;
    const tree = zg.tree;
    assert(tree.errors.len > 0);

    var msg: Writer.Allocating = .init(gpa);
    defer msg.deinit();
    const msg_bw = &msg.writer;

    var notes: std.ArrayList(Zoir.CompileError.Note) = .empty;
    defer notes.deinit(gpa);

    var cur_err = tree.errors[0];
    for (tree.errors[1..]) |err| {
        if (err.is_note) {
            tree.renderError(err, msg_bw) catch return error.OutOfMemory;
            try notes.append(gpa, try zg.errNoteTok(err.token, "{s}", .{msg.written()}));
        } else {
            // Flush error
            tree.renderError(cur_err, msg_bw) catch return error.OutOfMemory;
            const extra_offset = tree.errorOffset(cur_err);
            try zg.addErrorTokNotesOff(cur_err.token, extra_offset, "{s}", .{msg.written()}, notes.items);
            notes.clearRetainingCapacity();
            cur_err = err;

            // TODO: `Parse` currently does not have good error recovery
            // mechanisms, so the remaining errors could be bogus. As such,
            // we'll ignore all remaining errors for now. We should improve
            // `Parse` so that we can report all the errors.
            return;
        }
        msg.clearRetainingCapacity();
    }

    // Flush error
    const extra_offset = tree.errorOffset(cur_err);
    tree.renderError(cur_err, msg_bw) catch return error.OutOfMemory;
    try zg.addErrorTokNotesOff(cur_err.token, extra_offset, "{s}", .{msg.written()}, notes.items);
}