Latex caption + cross-referencing in bookdown

[nielsbock]

This is a fix for #1610 and #818. This PR adds a caption component to the LaTex outputs and enables cross-referencing in bookdown.

Adding a caption with tab_caption()

mtcars[1:5, ] %>%
  gt() %>% 
  tab_caption(md("This is a caption for **mtcars**")) %>% 
  as_latex() %>% 
  as.character()

results in the following Latex code:

"\\begin{table}[!t]\n\\caption{This is a caption for \\textbf{mtcars}} \n\\fontsize{12.0pt}{14.4pt}\\selectfont\n\\begin{tabular*}{\\linewidth}{@{\\extracolsep{\\fill}}rrrrrrrrrrr}\n\\toprule\nmpg & cyl & disp & hp & drat & wt & qsec & vs & am & gear & carb \\\\ \n\\midrule\\addlinespace[2.5pt]\n21.0 & 6 & 160 & 110 & 3.90 & 2.620 & 16.46 & 0 & 1 & 4 & 4 \\\\ \n21.0 & 6 & 160 & 110 & 3.90 & 2.875 & 17.02 & 0 & 1 & 4 & 4 \\\\ \n22.8 & 4 & 108 & 93 & 3.85 & 2.320 & 18.61 & 1 & 1 & 4 & 1 \\\\ \n21.4 & 6 & 258 & 110 & 3.08 & 3.215 & 19.44 & 1 & 0 & 3 & 1 \\\\ \n18.7 & 8 & 360 & 175 & 3.15 & 3.440 & 17.02 & 0 & 0 & 3 & 2 \\\\ \n\\bottomrule\n\\end{tabular*}\n\\end{table}\n"

I've updated knitr helper functions in knitr-utils.R which enables cross-referencing using bookdown. This only works in HTML if options("htmltools.preserve.raw" = FALSE), which was already commented in the code. For the Latex output in Quarto, I've used the function check_quarto() to disable captions created with tab_captions as it is not compatible with tbl-cap. This is not an issue with HTML in quarto; however, tbl-cap should still be used for cross-referencing.

[olivroy]

I am not using bookdown, so can't comment on this, but I made some suggestions in the tests to conform to new test style.

[nielsbock]

Thanks @olivroy. I modified the test to match the new style.

[olivroy]

Thanks for working on this and addressing the comments!

@rich-iannone I don't have much objection here. If this can help some bookdown users, we may as well go for it!

As long as it doesn't break the Quarto workflow which should still be to use tbl-cap: and label: tbl-*. i.e. tab_caption() is ignored in Quarto output iiuc.

[nielsbock]

No problem!

Yes, it shouldn't break Quarto workflow, as it's disabled in Quarto in the same way as the latex.tbl.pos argument in tab_options(), using the check_quarto() function. I've used gt with this code in both Quarto and Rmarkdown for academic work and haven't stumbled upon issues yet.

[rich-iannone]

LGTM!