Confusing error message when chunk option _dependson_ refers to file.info()

[otoomet]

I (mistakenly) write a code chunk like

# Markdown

```{r, dependson = file.info("test.rmd")}
# Need `cache.extra =`, not `dependson =` here
# Note: need name of a file that actually exists
"hi there!"
```

(I call this file test.rmd and compile as

$ Rscript -e "knitr::knit('test.rmd')"

)

Unfortunately, knitr gives an incomprehensible error message:

processing file: test.rmd
Error in defaults[[name]] : subscript out of bounds
Calls: <Anonymous> ... get -> setNames -> resolve -> setNames -> <Anonymous>
Execution halted

I'd expect a message along the lines

Processing code chunk 1... Invalid chunk name for 'dependson' option at line 3.

(This seems only to happen if the file.info refers to an existing file, not to a non-existing file.)

Session info:

> xfun::session_info('knitr')
R version 4.4.1 (2024-06-14)
Platform: x86_64-pc-linux-gnu
Running under: Ubuntu 20.04.6 LTS

Locale:
  LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
  LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
  LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
  LC_PAPER=en_US.UTF-8       LC_NAME=C                 
  LC_ADDRESS=C               LC_TELEPHONE=C            
  LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

Package version:
  evaluate_1.0.1  graphics_4.4.1  grDevices_4.4.1 highr_0.11     
  knitr_1.48.6    methods_4.4.1   stats_4.4.1     tools_4.4.1    
  utils_4.4.1     xfun_0.48       yaml_2.3.10    

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[yihui]

Thanks for the suggestion! Invalid dependson values will no longer trigger an error, and a warning message will be issued.

Accidentally, dependson = file.info("test.rmd") will work fine, even though you meant to use cache.extra (the chunk option name doesn't matter; it's the value that matters for caching).