R devel - Jul 2019 - Writing files with long paths on Windows fails even after enabling long paths

Hello all,

We now can have long file paths on Windows by setting the LongPathsEnabled
key to 1 at HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem
in the Registry Editor. I can successfully rename files to have long paths
in File Explorer.

R still isn't able to take advantage of the change, however:

write(1, paste0(paste(sample(letters, 265, TRUE), collapse = ''),
'.txt'))
#> Warning in file(file, ifelse(append, "a", "w")):
cannot open file
#>
'mbpbzpgivtyhuugkkbcfxlvdzhsujaivaissyhivwqdxixmbnzctxlplazgtewpiioyxielkbohmvejcdkhcjmqtjyieymccrfquiwepngrseroiolayuucevztmqemnlnvfsshyhhggakxfemzzovwikusqtfeslwevxqmvufuyyvgvwwubmmpzvlcwaiwhipumrzphyeziwibisxszqrouekuonzjlaztdtonuupniqmxsaifpvkcldftkgnkozntgndwfu.txt':
#> No such file or directory
#> Error in file(file, ifelse(append, "a", "w")): cannot
open the connection

I have read that long paths will be enabled by default in some future
release of Windows.

Hope this helps,
Kenny

	[[alternative HTML version deleted]]

Thanks for the note. R uses MAX_PATH internally at a number of places 
(both directly in Windows specific code and indirectly via PATH_MAX to 
reflect POSIX) and sometimes uses POSIX functions to access files and 
directories, so it would be a non-trivial change and would require more 
Windows-specific code in the code base. I expect external libraries to 
also depend on MAX_PATH and sometimes use POSIX functions (when 
supported on Windows) to access files and directories. Mingw which we 
use on Windows also has PATH_MAX derived from MAX_PATH to reflect POSIX 
behavior and allow use of POSIX-like functions.? It is hence even 
unclear how big effect this change if done in R could have on R end 
users, the limit would just remain in many situations. So I am afraid 
the path length limit on Windows in R cannot be removed/increased in the 
near future. Please feel free to submit a wishlist report to bugzilla, 
where this could be revisited in the future.

Best
Tomas

On 7/24/19 8:43 AM, Kenny Bell wrote:
> Hello all,
>
> We now can have long file paths on Windows by setting the LongPathsEnabled
> key to 1 at HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem
> in the Registry Editor. I can successfully rename files to have long paths
> in File Explorer.
>
> R still isn't able to take advantage of the change, however:
>
> write(1, paste0(paste(sample(letters, 265, TRUE), collapse = ''),
'.txt'))
> #> Warning in file(file, ifelse(append, "a", "w")):
cannot open file
> #>
>
'mbpbzpgivtyhuugkkbcfxlvdzhsujaivaissyhivwqdxixmbnzctxlplazgtewpiioyxielkbohmvejcdkhcjmqtjyieymccrfquiwepngrseroiolayuucevztmqemnlnvfsshyhhggakxfemzzovwikusqtfeslwevxqmvufuyyvgvwwubmmpzvlcwaiwhipumrzphyeziwibisxszqrouekuonzjlaztdtonuupniqmxsaifpvkcldftkgnkozntgndwfu.txt':
> #> No such file or directory
> #> Error in file(file, ifelse(append, "a", "w")):
cannot open the connection
>
> I have read that long paths will be enabled by default in some future
> release of Windows.
>
> Hope this helps,
> Kenny
>
> 	[[alternative HTML version deleted]]
>
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