Kable table where booktabs and collapse_rows with the first column "stacked" fails to produce pdf after R/Rstudio/tinytex update

Question

I recently updated my RStudio version to Version 1.4.1106, my R version to 4.0.5 (2021-03-31) -- "Shake and Throw". This was prompted by a particularly troublesome tinytex installation. Since that time I have been unable to get .rmd to knit into .pdf if I have any kable tables with the first column collapsed into subheadings using collapse_rows(row_group_label_position = "stack"). I use this with booktabs = TRUE for better looking tables. These .rmd would knit perfectly before the update. Now I get the particularly unhelpful LaTeX error:

"! Misplaced \noalign.
\addlinespace ->\noalign 
                         {\ifnum 0=`}\fi \@ifnextchar [{\@addspace }{\@addsp...
l.177 \addlinespace
                   [0.3em]  

This typically means I have an un-escaped special character in my table. However, now this happens without special characters. This only occurs if booktabs = TRUE and collapse_rows(row_group_label_position = "stack") changing booktabs to FALSE or row_group_label_position = "identity" will knit a table.

My reprex is below:

knitr::opts_chunk$set(echo = TRUE)

library(knitr)
library(kableExtra)
library(magrittr)

df <- 
    data.frame(stringsAsFactors=FALSE,
               a = c("a", "a", "a", "a", "a", "a", "b", "b", "b", "b", "b", "b"),
               b = c("a1", "a1", "a1", "a2", "a2", "a2", "b1", "b1", "b1", "b2",
                     "b2", "b2"),
               c = 1:12,
               d = c("Lorem ipsum dolor sit amet", "consectetur adipiscing elit", 
                     "sed do eiusmod tempor", "incididunt ut labore et", 
                     "dolore magna aliqua", "Ut enim ad minim veniam", 
                     "quis nostrud exercitation ullamco", "laboris nisi ut aliquip", 
                     "ex ea commodo consequat", "Lorem ipsum dolor sit amet", 
                     "consectetur adipiscing elit", "sed do eiusmod tempor"))

df %>% 
  kable("latex", booktabs = TRUE) %>% 
  collapse_rows(columns = 1:2, 
                row_group_label_position = "stack")

Answer 1

As reported in the kableExtra repo on Github, this is caused by a change in the latest version of knitr, and has been fixed in the dev version. Before a new release appears on CRAN, the dev version can be installed:

remotes::install_github('yihui/knitr')