untar() can fail strangely on Windows causing confusing error message in renv::restore()

[AshesITR]

I had a problem with renv::restore() because untar() used tar.exe from Git for Windows.
That version of tar needs paths like /C/myfile.tar.gz instead of C:/myfile.tar.gz and throws the error message

/usr/bin/tar: Cannot connect to C: resolve failed

While the problem can be fixed locally using Sys.setenv(TAR = ...) to another version of tar, the error is far from obvious, because renv stops with the error file not found (as it tries to download the same tarball from another repo which may not contain the package in question).

If renv:::renv_archive_list_impl used a specific version of tar (maybe installed with renv::equip()?) or used tar = "internal", the error would not occur.

[kevinushey]

Thanks for the bug report! I agree that using R's internal tar here is the right approach. I've made a change in the development version of renv here:

cd7a564

Let me know if this seems like the right solution. It does change the value of the TAR environment variable globally when renv is loaded (only if it was unset previously).

[kevinushey]

As an aside, newer versions of Windows come with their own tar implementation, e.g. at

C:\Windows\System32\tar.exe

so I wonder if we could / should use that instead of R's internal implementation as well.

[AshesITR]

That Version does work, as does the one shipping with RTools (tested 3.5 and 4.0)

Not you don't need to set TAR, it can be passed as an argument to untar in the various places renv calls it.

[AshesITR]

@kevinushey I'd avoid Sys.setenv() like this:

Change

renv/R/archive.R

Line 23 in 2f61943

tar = untar(path, list = TRUE),

to

tar = untar(path, list = TRUE, tar = Sys.getenv("TAR", unset = if (renv_platform_windows()) "internal" else ""))