Fix the issue with SQL chunk when cache=TRUE and output.var is specified

[yutannihilation]

fixes rstudio/rmarkdown#914

IIUC, SQL chunk is special in the sense the result of it can be either a text output or a data.frame, depending on whether output.var is set or not. Since both can be saved as an R object, it may be possible to use the same cache file. But, for simplicity and consistency with other engines (non-R engines seem to have their own cache file other than one for text outputs), I implemented to cache using the separate file, suffixed _sql_result.rds.

[yihui]

Thanks! Actually I just realized that there could be a much easier fix:

knitr/R/block.R

Line 114 in 4b64980

if (options$engine == 'stan') options$engine.opts$x else character(0)

I think we can just change it to

switch(
  options$engine,
  'stan' = options$engine.opts$x, 'sql' = options$output.var
)

Can you test that?

[yutannihilation]

Thanks, confirmed! It looks perfect. I didn't understand the way how object is passed to cache.

Since this PR seems superseded by your idea, I'm closing this. I'll try to achieve some actual contribution next time! 💪

[yihui]

Please go ahead to submit another PR with my approach above. Thanks! :)

[yutannihilation]

Hmm, generally, I rather hesitate to be the author of other people's idea... But, if you say so, I will. Thanks for always trying to educate me :)

[yihui]

Haha, actually I almost merged this PR, and I suddenly remembered I did something special for the stan engine. It turned out that the sql engine could use the same idea.