Pandoc Version Check: Best Practices For R Markdown Availability

Aug 7, 2025 by Rajiv Sharma 65 views

Pandoc Version Report: Clarifying How to Check for {rmarkdown} Availability

Hey everyone,

I stumbled upon the pandoc version reporting function within this package and wanted to discuss a point about how we check for {rmarkdown}'s availability. Specifically, I'm wondering if using isNamespaceLoaded() is the best approach, or if checking whether {rmarkdown} is installed might be a better alternative.

The Issue with `isNamespaceLoaded()`

My concern arises from a specific scenario. Imagine you're in a fresh R session, meaning {rmarkdown} hasn't been loaded yet. In this state, if you run the following function:

get_pandoc_version <- function() {
  if (isNamespaceLoaded("rmarkdown")) {
    ver <- rmarkdown::find_pandoc()
    if (is.null(ver$dir)) {
      "NA (via rmarkdown)"
    } else {
      paste0(ver$version, " @ ", ver$dir, "/ (via rmarkdown)")
    }
  } else {
    path <- Sys.which("pandoc")
    if (path == "") {
      "NA"
    } else {
      ver <- parse_pandoc_version(path)
      paste0(ver, " @ ", path)
    }
  }
}

parse_pandoc_version <- function(path) {
  tryCatch(
    {
      out <- system2(path, "--version", stdout = TRUE)[1]
      last(strsplit(out, " ", fixed = TRUE)[[1]])
    },
    error = function(e) "NA"
  )
}

Before calling rmarkdown::find_pandoc(), the get_pandoc_version() function returns "NA" because {rmarkdown} hasn't been loaded.

> get_pandoc_version()
[1] "NA"

However, after you explicitly call rmarkdown::find_pandoc(), even without attaching the entire rmarkdown}** package, the function now correctly detects the pandoc version. This is because `rmarkdown:find_pandoc()` loads the **{rmarkdown namespace, which subsequently makes isNamespaceLoaded("rmarkdown") return TRUE.

> rmarkdown::find_pandoc()
$version
[1] ‘3.6.3’

$dir
[1] "c:\\Program Files\\Positron\\resources\\app\\quarto\\bin\\tools"
> get_pandoc_version()
[1] "3.6.3 @ c:\\Program Files\\Positron\\resources\\app\\quarto\\bin\\tools/ (via rmarkdown)"

This behavior might be a bit misleading. The user might assume that pandoc wasn't detected initially, but it was actually just that {rmarkdown} hadn't been loaded yet.

Why Checking for Installation Might Be Better

Instead of relying on isNamespaceLoaded(), we could consider checking if the {rmarkdown} package is actually installed on the system. This would provide a more accurate picture of whether the package's functions are available, regardless of whether the namespace is currently loaded.

How to Check for Package Installation

R provides a couple of ways to check for package installation. One common method is using the requireNamespace() function with the quietly = TRUE argument. This function attempts to load the namespace but returns FALSE if the package isn't installed, without printing any messages to the console. Another option is to use find.package(), which will return the path to the installed package if it exists and throw an error if it doesn't.

Revised `get_pandoc_version()` Function

Here's how we could modify the get_pandoc_version() function to check for package installation using requireNamespace():

get_pandoc_version <- function() {
  if (requireNamespace("rmarkdown", quietly = TRUE)) {
    ver <- rmarkdown::find_pandoc()
    if (is.null(ver$dir)) {
      "NA (via rmarkdown)"
    } else {
      paste0(ver$version, " @ ", ver$dir, "/ (via rmarkdown)")
    }
  } else {
    path <- Sys.which("pandoc")
    if (path == "") {
      "NA"
    } else {
      ver <- parse_pandoc_version(path)
      paste0(ver, " @ ", path)
    }
  }
}

With this change, the function will only attempt to use rmarkdown::find_pandoc() if the {rmarkdown} package is actually installed. If it's not installed, it will fall back to the Sys.which("pandoc") method, providing a more consistent and accurate result.

Benefits of Checking for Installation

More Accurate Detection: Checking for installation provides a clearer indication of whether {rmarkdown}'s functions are genuinely available.
Avoids Misleading Results: It prevents the situation where pandoc is detected only after rmarkdown::find_pandoc() is called, even if the package isn't fully loaded.
Improved User Experience: It offers a more consistent and predictable behavior, enhancing the overall user experience.

Alternatives and Considerations

Of course, there are other approaches we could consider. For instance, we could use tryCatch() around the rmarkdown::find_pandoc() call to handle cases where the function might fail due to {rmarkdown} not being installed. However, checking for installation upfront seems like a more direct and efficient solution.

It's also worth noting that the current approach might be intentional, perhaps to minimize the number of dependencies loaded by default. However, in this specific case, I believe the benefits of checking for installation outweigh the potential drawbacks.

Conclusion: Let's Discuss!

So, what do you guys think? Should we switch to checking for {rmarkdown} installation instead of relying on isNamespaceLoaded()? I'm eager to hear your perspectives and discuss the best way forward. This small change could lead to a more robust and user-friendly way of reporting the pandoc version.

By focusing on the actual installation status, we ensure a more reliable and consistent detection mechanism. This not only simplifies the process but also reduces potential confusion for users. The proposed change aligns with the goal of providing accurate information about system dependencies, thereby enhancing the overall utility of the package. Let's work together to refine this function and ensure it delivers the best possible experience for everyone!

Further enhancements could include providing more informative messages to users if pandoc is not found or if {rmarkdown} is not installed. For example, we could suggest installing pandoc or the {rmarkdown} package, which would be particularly helpful for new users. Additionally, we might consider adding a configuration option to allow users to specify the path to pandoc manually, which could be useful in cases where pandoc is installed in a non-standard location.

The key takeaway is that a small adjustment in how we check for dependencies can have a significant impact on the accuracy and usability of the function. By prioritizing clarity and user experience, we can make our tools more effective and accessible to a wider audience. I look forward to hearing your thoughts and collaborating on this improvement.

Let's make sure that our package provides the most accurate and helpful information possible! This discussion is a great step towards ensuring that our users have a smooth and intuitive experience when working with our tools. Your insights and expertise are highly valued, and I believe that together, we can make this function even better. Thank you for taking the time to consider this issue, and I am excited to see where this conversation leads us.