I don't know what the warning looks like, but the ?tar help page discusses the issues.

Duncan Murdoch

On 12/12/2023 3:10 p.m., Ben Bolker wrote:
   FWIW the R-windows FAQ says:

Yet another complication is a 260 character limit on the length of the
entire path name imposed by Windows. The limit applies only to some
system functions, and hence it is possible to create a long path using
one application yet inaccessible to another. It is sometimes possible to
reduce the path length by creating a drive mapping using subst and
accessing files via that drive. As of Windows 10 version 1607 and R 4.3,
one can remove this limit via Windows registry by setting
Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem\LongPathsEnabled
to 1. Long paths still may not always work reliably: some applications
or packages may not be able to work with them and Windows cannot execute
an application with long path as the current directory.

    I'm having trouble finding the specific check for path lengths > 100
in the R source tree.  It would be helpful to have the exact wording of
the NOTE/WARNING (?) that is thrown ...  (I know I could make my own
mini-package with a long path length in it somewhere but ...)

    cheers
     Ben Bolker

On 2023-12-12 2:57 p.m., Simon Urbanek wrote:
Justin,

now that you clarified what you are actually talking about, this is a question 
about the CRAN policies, so you should really direct it to the CRAN team as it 
is their decision (R-devel would be appropriate if this was a limitation in R 
itself, and R-package-devel would be appropriate if you wanted help with 
refactoring to adhere to the policy). There are still path limits on various 
platforms (even if they are becoming more rare), so I'd personally question the 
source rather than the policy, but then your email was remarkably devoid of any 
details.

Cheers,
Simon


On Dec 13, 2023, at 6:03 AM, McGrath, Justin M <jmcgr...@illinois.edu> wrote:

When submitting a package to CRAN, it is required that path names be shorter 
than 100 bytes, with the reason that paths longer than that cannot be made into 
portable tar files. This error is reported by `R CMD check --as-cran`. Since 
this pertains only to developing packages, this seemed like the appropriate 
list, but if you don't think so, I can instead ask on R-devel.

Best wishes,
Justin

________________________________________
From: Martin Maechler <maech...@stat.math.ethz.ch>
Sent: Tuesday, December 12, 2023 10:13 AM
To: McGrath, Justin M
Cc: r-package-devel@r-project.org
Subject: Wrong mailing list: [R-pkg-devel] Could the 100 byte path length limit 
be lifted?

McGrath, Justin M
     on Tue, 12 Dec 2023 15:03:28 +0000 writes:

We include other software in our source code. It has some long paths so a few 
of the files end up with paths longer than 100 bytes, and we need to manually 
rename them whenever we pull in updates.
The 100 byte path limit is from tar v7, and since
POSIX1.1988, there has not been a path length limit. That
standard is 35 years old now, so given that there is
probably no one using an old version of tar that also
wants to use the latest version of R, could the 100 byte
limit be lifted? Incidentally, I am a big proponent of
wide, long-term support, but it's hard to see that this
change would negatively impact anyone.

Best wishes,
Justin

Wrong mailing list:

This is a topic for R-devel,  not at all R-package-devel,
but be more accurate in what you are talking about, only between
the line I could read that it is about some variants of using
'tar'.

Best regards,
Martin
---

Martin Maechler
ETH Zurich  and  R Core team

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