Creating a pdf using Quarto, can't put a line break in a column table

Here is a sample of my code, where I want to break up the column "Sepal.Length" on two lines.

---
title: "Unbreakable Line"
format: pdf
editor: visual
---

{r}
#| label: load-packages
#| include: false

library(tidyverse)
library(magrittr)
library(tinytex)
library(gt)


{r}

iris %>% 
  head(10) %>% 
  gt() %>% 
    cols_label(
      Sepal.Length = md("Sepal<br>Length")
    )

It works fine when I preview the chunk, but when I render, I get this error:

"Warning: HTML tags found, and they will be removed.* Set options(gt.html_tag_check = FALSE) to disable this check."

I've tried taking out the md() and using "\n", but that just gives me a space. Any hints on how to get a line break here?

First, as you are rendering to pdf HTML tags will not work and get dropped as the warning is telling you. Instead, you have to use LaTex to add a linebreak, e.g. you can use \\\\. However, this will not work either as under the hood the backslashes get escaped and replaced with \\textbackslash{} in the resulting LaTeX code.

To prevent the escaping, functions from other packages like knits::kable or gtsummary::as_kable_extra offer an escape= parameter which can be set to FALSE. This is however not the case for gt::as_latex.

One possible workaround to fix that would be to use a custom knit_print method to overwrite the knit_print method provided by gt. Doing so allows to replace the \\textbackslash{} added by gt::as_latex with the desired \\. Basically the same is done under the hood by e.g. gtsummary::as_kable_extra.

Note: You have to define or add the custom knit_print method after loading gt, otherwise it gets overridden by the gt default.

---
title: "Unbreakable Line"
format: pdf
editor: visual
---

```{r}
#| label: load-packages
#| include: false

library(tidyverse)
library(tinytex)
library(gt)
```

```{r echo=FALSE}
knit_print.gt_tbl <- function(x, ...) {
  if (knitr::is_latex_output()) {
    res <- gt::as_latex(x)
    res[[1]] <- gsub(
      "\\textbackslash{}",
      "\\",
      res[[1]],
      fixed = TRUE
    )

    return(res)
  }

  gt:::knit_print.gt_tbl(x)
}

registerS3method(
  "knit_print", "gt_tbl", knit_print.gt_tbl,
  envir = asNamespace("knitr")
)
```

```{r echo=FALSE}
iris %>%
  head(10) %>%
  gt() %>%
  cols_label(
    Sepal.Length = "Sepal\\\\Length"
  )
```