Underscore in names causes TeX error

[potash]

I am trying to compile the following Rmd file:

    ---
    output: pdf_document
    ---
   
    ```{r dev='tikz'}
    library(ggplot2)
    df <- expand.grid(x = 0:5, y = 0:5)
    df$z <- runif(nrow(df))
    # default is compatible with geom_tile()
    ggplot(df, aes(x, y, fill = z)) + geom_raster()
    ```

I get the following error:

! Missing $ inserted.
<inserted text> 
                $
l.69 ...interpolate=false]{unnamed-chunk-1-1_ras1}
                                                  }; 

Quitting from lines 6-11 (test.Rmd) 

I believe the issue is that the chunk is generating a helper raster file and using the suffix "_ras1" but TeX uses underscore for subscripts. I don't know if this is an issue in tikzDevice or elsewhere in the Rmarkdown toolchain. Appreciate your help.

[rstub]

This has been asked on SO: https://stackoverflow.com/q/58401825/8416610 Unfortunately I have not found a solution for it at the time. I will look again.

[rstub]

@potash The current development version of knitr solves this problem for me. Can you please verify on your end?