yaml_front_matter throws error if YAML ends with comment that ends with a :.

[keithnewman]

Expected behaviour

A line starting with # would be treated as a comment and not affect the parsing of the rest of a YAML block when using yaml_front_matter().

Actual behaviour

If the YAML block ends with a comment that ends the line with a colon, that colon causes yaml_front_matter() to return a parsing error because the YAML ends in :, despite the colon being part of a comment. The comment can exist earlier on in the YAML, as long as it has another term afterwards.

Reprex (CRAN version)

Make two Rmd files, with the same lines of YAML, but swapping the author and (commented out) date lines around.

file.create("okay.Rmd")
#> [1] TRUE
okay <- file("okay.Rmd")
writeLines(
  c(
    '---',
    'title: "My document name"',
    ' # date:',
    'author: "Me"',
    '---',
    'Document body'
  ),
  con = okay
)
close(okay)

file.create("not_okay.Rmd")
#> [1] TRUE
not_okay <- file("not_okay.Rmd")
writeLines(
  c(
    '---',
    'title: "My document name"',
    'author: "Me"',
    ' # date:',
    '---',
    'Document body'
  ),
  con = not_okay
)
close(not_okay)

rmarkdown::yaml_front_matter("okay.Rmd")
#> $title
#> [1] "My document name"
#> 
#> $author
#> [1] "Me"
rmarkdown::yaml_front_matter("not_okay.Rmd")
#> Error: Invalid YAML front matter (ends with ':')

xfun::session_info('rmarkdown')
#> R version 4.3.0 (2023-04-21)
#> Platform: x86_64-pc-linux-gnu (64-bit)
#> Running under: Ubuntu 22.04.2 LTS
#> 
#> 
#> Locale:
#>   LC_CTYPE=en_GB.UTF-8       LC_NUMERIC=C              
#>   LC_TIME=en_GB.UTF-8        LC_COLLATE=en_GB.UTF-8    
#>   LC_MONETARY=en_GB.UTF-8    LC_MESSAGES=en_GB.UTF-8   
#>   LC_PAPER=en_GB.UTF-8       LC_NAME=C                 
#>   LC_ADDRESS=C               LC_TELEPHONE=C            
#>   LC_MEASUREMENT=en_GB.UTF-8 LC_IDENTIFICATION=C       
#> 
#> time zone: Europe/London
#> tzcode source: system (glibc)
#> 
#> Package version:
#>   base64enc_0.1.3   bslib_0.4.2       cachem_1.0.8      cli_3.6.1        
#>   digest_0.6.31     ellipsis_0.3.2    evaluate_0.20     fastmap_1.1.1    
#>   fontawesome_0.5.1 fs_1.6.2          glue_1.6.2        graphics_4.3.0   
#>   grDevices_4.3.0   highr_0.10        htmltools_0.5.5   jquerylib_0.1.4  
#>   jsonlite_1.8.4    knitr_1.42        lifecycle_1.0.3   magrittr_2.0.3   
#>   memoise_2.0.1     methods_4.3.0     mime_0.12         R6_2.5.1         
#>   rappdirs_0.3.3    rlang_1.1.1       rmarkdown_2.21    sass_0.4.5       
#>   stats_4.3.0       stringi_1.7.12    stringr_1.5.0     tinytex_0.45     
#>   tools_4.3.0       utils_4.3.0       vctrs_0.6.2       xfun_0.39        
#>   yaml_2.3.7       
#> 
#> Pandoc version: 2.19.2

^{Created on 2023-05-03 with reprex v2.0.2}

I had the same result in R 4.2.1.

Reprex (development version)

file.create("okay.Rmd")
#> [1] TRUE
okay <- file("okay.Rmd")
writeLines(
  c(
    '---',
    'title: "My document name"',
    ' # date:',
    'author: "Me"',
    '---',
    'Document body'
  ),
  con = okay
)
close(okay)

file.create("not_okay.Rmd")
#> [1] TRUE
not_okay <- file("not_okay.Rmd")
writeLines(
  c(
    '---',
    'title: "My document name"',
    'author: "Me"',
    ' # date:',
    '---',
    'Document body'
  ),
  con = not_okay
)
close(not_okay)

rmarkdown::yaml_front_matter("okay.Rmd")
#> $title
#> [1] "My document name"
#> 
#> $author
#> [1] "Me"
rmarkdown::yaml_front_matter("not_okay.Rmd")
#> Error: Invalid YAML front matter (ends with ':')

xfun::session_info('rmarkdown')
#> R version 4.3.0 (2023-04-21)
#> Platform: x86_64-pc-linux-gnu (64-bit)
#> Running under: Ubuntu 22.04.2 LTS
#> 
#> 
#> Locale:
#>   LC_CTYPE=en_GB.UTF-8       LC_NUMERIC=C              
#>   LC_TIME=en_GB.UTF-8        LC_COLLATE=en_GB.UTF-8    
#>   LC_MONETARY=en_GB.UTF-8    LC_MESSAGES=en_GB.UTF-8   
#>   LC_PAPER=en_GB.UTF-8       LC_NAME=C                 
#>   LC_ADDRESS=C               LC_TELEPHONE=C            
#>   LC_MEASUREMENT=en_GB.UTF-8 LC_IDENTIFICATION=C       
#> 
#> time zone: Europe/London
#> tzcode source: system (glibc)
#> 
#> Package version:
#>   base64enc_0.1.3   bslib_0.4.2       cachem_1.0.8      cli_3.6.1        
#>   digest_0.6.31     ellipsis_0.3.2    evaluate_0.20     fastmap_1.1.1    
#>   fontawesome_0.5.1 fs_1.6.2          glue_1.6.2        graphics_4.3.0   
#>   grDevices_4.3.0   highr_0.10        htmltools_0.5.5   jquerylib_0.1.4  
#>   jsonlite_1.8.4    knitr_1.42        lifecycle_1.0.3   magrittr_2.0.3   
#>   memoise_2.0.1     methods_4.3.0     mime_0.12         R6_2.5.1         
#>   rappdirs_0.3.3    rlang_1.1.1       rmarkdown_2.21.3  sass_0.4.5       
#>   stats_4.3.0       stringi_1.7.12    stringr_1.5.0     tinytex_0.45     
#>   tools_4.3.0       utils_4.3.0       vctrs_0.6.2       xfun_0.39        
#>   yaml_2.3.7       
#> 
#> Pandoc version: 2.19.2

^{Created on 2023-05-03 with reprex v2.0.2}

Checklist

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• included a minimal, self-contained, and reproducible example?

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[cderv]

The error comes from

rmarkdown/R/output_format.R

Lines 727 to 731 in 9568cde

	validate_front_matter <- function(front_matter) {
	front_matter <- trim_trailing_ws(front_matter)
	if (grepl(":$", front_matter))
	stop2("Invalid YAML front matter (ends with ':')")
	}

We purposely error since the start to warn user for an incomplete front matter that would cause (at the time) YAML parsing issue.
Changes are from 9 years ago : a13c13f and 59c22ff

So this is by design, and we do not account for comment in the validation. (we could try though)

However, I am wondering if we should still validate.

This is called in

rmarkdown/R/output_format.R

Lines 713 to 714 in 9568cde

	validate_front_matter(front_matter)
	parsed_yaml <- yaml_load(front_matter)

to prevent the hang in yaml_load() . Maybe this is not needed anymore. If the YAML is malformed, we'll get an error

> yaml_load('"title: \"My document name\"\nauthor: \"Me\"\ndate:"')
Error in yaml::yaml.load(..., eval.expr = TRUE) : 
  Parser error: did not find expected <document start> at line 1, column 10

@yihui what do you think ?

[yihui]

I think we can get rid of the validation.

[cderv]

Thanks I went with removal. I don't think this internal function is used anywhere else (I checked Quarto and RStudio IDE and Connect)

[github-actions]

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