Cached code chunks able to depend on external files

[karimn]

Description

It would be very helpful if a code chunk is able to use dependson to capture the dependency on a file as well as another chunk. This could be helpful when we need to check if a data file has changed or a compiled source file has been updated.

[mcanouil]

Could you elaborate? The option you seemed to describe is a knitr option and I don't why it would not work.

[karimn]

It would be nice to be able to do something like

```{r}
#| dependson: my_data.rds

my_data <- read_rds("my_data.rds")
```

or

```{r}
#| dependson: my_model.stan

my_model <- cmdstanr::cmdstan_model("my_model.stan")
```

[mcanouil]

Is it not what targets does?
And knitr when using this option and caching?
Note that dependson is a knitr option used to create code cells dependencies.
So Quarto cannot use that as you describe.

You should really take a look at targets which is compatible with Quarto, especially since you seem to focus only on R.

[karimn]

targets does look very interesting. I looked here https://books.ropensci.org/targets/literate-programming.html but it doesn't seem to be aware of dependencies between chunks. Are there any plans to incorporate them more closely?

[mcanouil]

The whole purpose of targets is to deal with dependencies between "target" or "chunk" in literate programming.
There is even a figure showing that in the link you shared.

[jaredlander]

You can achieve this using the cache.extra chunk option.

```{r}
#| cache.extra: !expr file.mtime("my_model.stan")

my_model <- cmdstanr::cmdstan_model("my_model.stan")
```