Caching sql chunks throwing error when output.var not used

[mfherman]

I'm having trouble knitting an Rmd when I set cache=TRUE for sql code chunks.

There is some discussion of a related error #1544 and rstudio/rmarkdown#914, but those examples seem to be when output.var is set in the sql chunk and the bug was fixed a couple years ago.

The following Rmd will knit the first time, but the second time when it tries to read from the cache, I get this error:

Quitting from lines 12-13 (test-sql-cache-rmd.Rmd) 
Error in fun(environment()) : invalid first argument
Calls: <Anonymous> ... call_block -> <Anonymous> -> lazyLoad -> lazyLoadDBexec -> fun
Execution halted

When cache=FALSE, the error goes away.

---
title: "sql chunk"
output: html_document
---

```{r setup, include=FALSE}
con <- DBI::dbConnect(RSQLite::SQLite(), ":memory:")
knitr::opts_chunk$set(echo = TRUE, connection = "con")
```

```{sql select_1, cache=TRUE}
SELECT 1
```

This issue was previously posed on RStudio Community.

> xfun::session_info("knitr")
R version 3.6.1 (2019-07-05)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 17134), RStudio 1.3.878

Locale:
  LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252    LC_MONETARY=English_United States.1252
  LC_NUMERIC=C                           LC_TIME=English_United States.1252    

Package version:
  evaluate_0.14   glue_1.4.0      graphics_3.6.1  grDevices_3.6.1 highr_0.8       knitr_1.28.5    magrittr_1.5    markdown_1.1    methods_3.6.1  
  mime_0.9        stats_3.6.1     stringi_1.4.6   stringr_1.4.0   tools_3.6.1     utils_3.6.1     xfun_0.13       yaml_2.2.1     

---

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[solarchemist]

Wow, this was a tricky bug.

I think I can add to it. This behaviour is present even with eval=FALSE. I had some chunks demoing SQL queries on my blog (using SQL chunks mostly for the sake of pretty code highlighting), and every blogdown run except the first would fail with:

Error in fun(environment()) : invalid first argument
Calls: local ... call_block -> <Anonymous> -> lazyLoad -> lazyLoadDBexec -> fun
Execution halted
Error in render_page(f) : 
  Failed to render 'content/post/2018-07-24-self-hosted-git-server/2018-07-24-gitea.Rmd'

When it failed, I would change it to a generic code chunk, and then it would run ok once before failing again the subsequent run. Anyway, thanks for explaining this weird behaviour!

This was my chunk options and code:

```{r global_options, echo=FALSE, results='hide', message=FALSE}
opts_chunk$set(
   eval    = TRUE,
   cache   = TRUE,
   message = FALSE,
   warning = FALSE)
```

```{sql eval=FALSE}
GRANT ALL ON gitea.* TO 'gitea'@'localhost';
FLUSH PRIVILEGES;
```

> xfun::session_info("knitr")
R version 3.6.2 (2019-12-12)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 18.04.4 LTS, RStudio 1.3.959

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       

Package version:
  evaluate_0.14   glue_1.4.1      graphics_3.6.2  grDevices_3.6.2 highr_0.8      
  knitr_1.28      magrittr_1.5    markdown_1.1    methods_3.6.2   mime_0.9       
  stats_3.6.2     stringi_1.4.6   stringr_1.4.0   tools_3.6.2     utils_3.6.2    
  xfun_0.15       yaml_2.2.1