Add rstudioapi shims for source markers

[juliasilge]

Originally posted by @etiennebacher in #6061:

I have a package where I use RStudio's source markers using rstudioapi::callFun("sourceMarkers", ...). Since this feature is not available in VS Code for instance, I put it behind rstudioapi::isAvailable(). However, it turns out that rstudioapi::isAvailable() returns TRUE in Positron, but source markers are not supported.

Will they be supported in the future? Alternatively, do I have a way to detect that the user is using Positron?

rstudioapi::isAvailable()
#> TRUE
rstudioapi::callFun("sourceMarkers")
#> Error:
#> ! Function sourceMarkers not found in RStudio

[juliasilge]

For more information:

https://rstudio.github.io/rstudioapi/reference/sourceMarkers.html

I'll be honest that I'm not familiar with this one, and it does look less commonly used than some of the other rstudioapi shims we need to support.

[etiennebacher]

it does look less commonly used than some of the other rstudioapi shims we need to support.

Yes, to be honest I think I've only seen used in lintr (and I use it in flint) to report lints in a separate tab in RStudio.

Nit: the search for the usage could include rstudioapi::callFun("sourceMarkers", ...):
https://github.com/search?q=rstudioapi::sourceMarkers%20OR%20rstudioapi::callFun(%22sourceMarkers%22&type=code&rgh-link-date=2025-01-22T00:28:04Z