Using rvest with drake: external pointer is not valid error - rvest

Question

When I first run the code below, everything is ok. But when I change something in html_file %>%... comand, for example commenting tolower(), I get the following error:
Error: target title failed.
diagnose(title)error$message:
external pointer is not valid
diagnose(title)error$calls:
1. └─html_file %>% html_nodes("h2") %>% html_text()
Code:
library(rvest)
library(drake)
some_string <- '
<div class="main">
<h2>A</h2>
<div class="route">X</div>
</div>
'
html_file <- read_html(some_string)
title <- html_file %>%
html_nodes("h2") %>%
html_text()
plan <- drake_plan(
html_file = read_html(some_string),
title = html_file %>%
html_nodes("h2") %>%
html_text() %>%
tolower()
)
make(plan)
I found two possible solutions but I'm not enthusiastic about them.
1. Join both steps in drake_plan into one.
2. Use xml2::write_html() and xml2::read_html() as suggested here.
Is there a better way to solve it?
P.S. Issue was already discussed here, Rstudio forum, and on github.

Answer 1

By default, drake saves targets as RDS files (other options here). So https://github.com/tidyverse/rvest/issues/181#issuecomment-395064636, which you brought up, is exactly the problem. I like (1) because text is compatible with RDS. Speaking broadly, it is up to the user to choose good targets compatible with drake's data storage system. See https://books.ropensci.org/drake/plans.html#how-to-choose-good-targets for a discussion and links to similar issues. But you want to go with (2), you could return the file path to your HTML file from within a dynamic file.