Support variable expansion in cache.path (e.g. cache/INPUT/FORMAT/)

[AlbertoFabbri93]

Description

Hi Quarto team,

I’d like to request support for variable expansion in the cache.path option inside _quarto.yml and document front matter.

Currently, in knitr’s documentation, the cache path is described as:

INPUT_cache/FORMAT/

where:

INPUT = the input filename (without extension)
FORMAT = the output format (html, pdf, docx, etc.)

However, when I try to set in _quarto.yml:

knitr:
  opts_chunk:
    cache.path: "shared_cache/INPUT/FORMAT/"
execute:
  cache: true

the literal string INPUT and FORMAT are not expanded. Instead, the cache directory is created at shared_cache/INPUT/FORMAT/.

Feature request:

Support token expansion in cache.path, so that users can write e.g. cache/INPUT/FORMAT/ in _quarto.yml, and Quarto will replace INPUT with the source file name and FORMAT with the target format name.

Why this is useful:

• It allows project-wide cache configuration without repeating setup code in each document.
• It enables safe cache sharing across multiple documents and formats, while preventing collisions.
• It makes cache folder naming consistent with the defaults used by knitr.

Right now, the only workaround is to programmatically set cache.path in a setup chunk using R code but this must be duplicated across documents, which isn’t as clean as a declarative _quarto.yml setting.

Thanks for considering this feature!

[cscheid]

Thanks for the request, but this is not something we will do because the potential for confusion is far too high.

[mcanouil]

1. For project-wide configuration, the options should be set in _quarto.yml.
2. After investigation, the behaviour is exactly the same as with R Markdown. Setting cache-path leads to all cache to be written in the directory being set by the user.

Take the following Quarto document quarto-cache.qmd:

---
title: "Cache"
format:
  html: default
  typst: default
execute:
  cache: true
---

```{r}
rnorm(10)
```

❯ tree quarto-cache_cache 
quarto-cache_cache
├── html
│   ├── __packages
│   ├── unnamed-chunk-1_6d52297f680715667de89e75ccdf4bb5.RData
│   ├── unnamed-chunk-1_6d52297f680715667de89e75ccdf4bb5.rdb
│   └── unnamed-chunk-1_6d52297f680715667de89e75ccdf4bb5.rdx
└── typst
    ├── __packages
    ├── unnamed-chunk-1_733527c90b181e7587d2d1e232ba7458.RData
    ├── unnamed-chunk-1_733527c90b181e7587d2d1e232ba7458.rdb
    └── unnamed-chunk-1_733527c90b181e7587d2d1e232ba7458.rdx

3 directories, 8 files

This is the INPUT_cache/FORMAT/... pattern.

Now let's compare with rmarkdown using rmarkdown-cache.rmd:

---
title: "Cache"
output:
  html_document: default
  pdf_document: default
---

```{r}
#| cache: true
rnorm(10)
```

❯ tree rmarkdown-cache_cache 
rmarkdown-cache_cache
├── html
│   ├── __packages
│   ├── unnamed-chunk-1_dc9020897fffba271d062d6828d12778.RData
│   ├── unnamed-chunk-1_dc9020897fffba271d062d6828d12778.rdb
│   └── unnamed-chunk-1_dc9020897fffba271d062d6828d12778.rdx
└── latex
    ├── __packages
    ├── unnamed-chunk-1_3cfbbd2805f549614e6e5c7c0b87bc30.RData
    ├── unnamed-chunk-1_3cfbbd2805f549614e6e5c7c0b87bc30.rdb
    └── unnamed-chunk-1_3cfbbd2805f549614e6e5c7c0b87bc30.rdx

3 directories, 8 files

Now, if you set cache-path, then it means "put everything in the directory I set" which is bad for multi-formats as one format overwrites the cache of the other.

---
title: "Cache"
output:
  html_document: default
  pdf_document: default
---

```{r}
#| cache: true
#| cache-path: shared_cache/
rnorm(10)
```

❯ tree shared_cache         
shared_cache
├── __packages
├── unnamed-chunk-1_5d0d0fbdccb42e859943b699a1b060c6.RData
├── unnamed-chunk-1_5d0d0fbdccb42e859943b699a1b060c6.rdb
└── unnamed-chunk-1_5d0d0fbdccb42e859943b699a1b060c6.rdx

1 directory, 4 files

Same thing happens in Quarto.
If you want to change the location of the cache, then you'll have to account for this behaviour as you opted out of the dynamic path location generation.

[AlbertoFabbri93]

Now, if you set cache-path, then it means "put everything in the directory I set" which is bad for multi-formats as one format overwrites the cache of the other.

Yes, exactly, that’s the problem. If I set a static cache.path in my _quarto.yml, all formats end up writing to the same location, so one format can overwrite the cache of another.

The issue becomes even more pronounced when working with multiple independent Quarto files in the same project, as the cache folders are no longer separated by file. This can lead to collisions when code chunks from different files share the same label (even though the checksum in the cache file names should, in theory, prevent this). That’s why I was asking whether it’s possible to move all cache folders into a single main directory while still preserving the dynamic generation of folder paths.

My main motivation is to declutter my working directory, which has started to become quite messy, as you can see here:

If I understand it correctly, the answer is that this is not possible in Knitr and it is therefore not possible in Quarto, right?

[cderv]

That’s why I was asking whether it’s possible to move all cache folders into a single main directory while still preserving the dynamic generation of folder paths.

This is not something yet possibly. It is a feature request, possibly in knitr to accept something like a cache.root-dir option while keeping the default cache.path logic.

EDIT:

• Allow to place all INPUT_cache folder into a single one when using cache for multi document project rstudio/rmarkdown#2603

[AlbertoFabbri93]

Thank you very much for opening the issue in rmarkdown!