Add attribute to repos, for renv users

[juliasilge]

Addresses posit-dev/positron#4255

You can check out the approach RStudio takes here:
https://github.com/rstudio/rstudio/blob/078e21116b0e34aff92addf961699017adb62fc5/src/cpp/r/R/Tools.R#L698

I saw your note here @DavisVaughan. Given that we are unlikely to be able to change this attribute in RStudio, I don't tend to think we will gain much by using IDE or default. If you have a strong opinion otherwise, happy to change this, though!

QA Notes

After this PR is merged and ark is bumped, you will see (edited after code review to change name of attribute):

getOption("repos")
#>                        CRAN 
#> "https://cran.rstudio.com/" 
#> attr(,"IDE")
#> [1] TRUE

^{Created on 2024-09-04 with reprex v2.1.1}

Notice the new attribute.

Once we get this into a release build, we should update at rstudio/renv#1963.

[DavisVaughan]

We should not unconditionally set this. IIUC, we should only set this if we detect the "default" repos behavior, i.e. if we see "@CRAN@" as the repos[["CRAN"]] value

That is what RStudio does

https://github.com/rstudio/rstudio/blob/078e21116b0e34aff92addf961699017adb62fc5/src/cpp/r/R/Tools.R#L682-L712

I think that means you only set the attribute in the if (identical(repos[["CRAN"]], "@CRAN@")) { branch

---

In theory this allows a user to set their own repos in their .Rprofile, and in that case we are not supposed to mark that with a "Positron" attribute, as that did not come from us. In practice that might not work, because I think this code might get run before we source a user's .Rprofile on their behalf, but that would be another bug to fix separately, I think.

[juliasilge]

Ah, I misunderstood before how this was being used! Thanks 👍

[DavisVaughan]

I have one other larger worry about this in general.

None of this is going to kick in if the user is using a version of R installed with Rig. That's because Rig sets repos for you in the special /library/base/R/Rprofile that R forcibly loads on every startup (like, rig straight up tweaks this file that you get when you download R itself)

That means that every time you load up a rig installed version of R, it will always have repos set and it will never be "@CRAN@".

https://github.com/r-lib/rig/blob/140115c9b565167670cfc6f303e6c968c563db98/src/windows.rs#L342
https://github.com/r-lib/rig/blob/140115c9b565167670cfc6f303e6c968c563db98/src/macos.rs#L788
https://github.com/r-lib/rig/blob/140115c9b565167670cfc6f303e6c968c563db98/src/linux.rs#L579-L613

That means we would never add the "Positron" attribute, and RStudio never adds the "RStudio" attribute.

I can confirm this by loading up my non-rig R-devel version in a plain terminal:

> getOption("repos")
    CRAN
"@CRAN@"

vs a rig installed R 4.4

> getOption("repos")
                         CRAN
"https://cloud.r-project.org"

Now, this may be ok for Positron because on Linux you can see in the above link that rig sets up PPM as the repos option, so that should mean that users get binaries when using renv + rig on Linux, even though renv isn't the one setting the repos option.

The bigger issue would be for renv itself, because it means that renv will never detect a "default" case and can't set the repos option to the user's chosen configuration option for ppm.url(), which defaults to normal PPM but can be customized by the user:
https://github.com/rstudio/renv/blob/fcfe748225a88bf56b1964868604353c2e73bf7c/R/init.R#L341

[DavisVaughan]

I do not think we should let this stop us from moving on this PR, but @kevinushey may want to take a closer look at this weird rig + renv intersection issue, especially the inability to set a user customized config$ppm.url()

[DavisVaughan]

@juliasilge if you do as I suggest above and only conditionally set repos[["CRAN"]] when you see it is set to "@CRAN@", then you aren't ever going to see a "Positron" attribute in your testing unless you swap to a non-rig version of R

[juliasilge]

I am not a rig user 😆 so I did not notice this.

I will add a note for renv when I say this new attribute is available.