iswritable(::FileName) is useless and broken

[gasagna]

There is probably a bug is the iswritable function. Watch this:

julia> iswritable("/")
true

shell> touch /new
touch: cannot touch '/new': Permission denied

All this is run from the REPL, with julia launched as normal user, so there is no write permission at all in the root folder /. I would expect iswritable to return false in this case.

Running Julia v"0.3.0-prerelease+3461" on Ubuntu 14.04.

[ivarne]

See also previous discussion on julia-users
https://groups.google.com/forum/#!topic/julia-users/V4sc2jyzDAQ

[gasagna]

@ivarne I opened that discussion and reported the issue here. Thanks for the cross-reference.

[JeffBezanson]

The documentation seems to be wrong. It says this refers to the current user, but it actually refers to any user.
Is there a way to test permissions against the current user without doing all the uid and group manipulation manually?

[ihnorton]

fixed in a487dcf

[timholy]

Nice, @ihnorton!

[ihnorton]

I guess we'll have to do it the bit-fiddly way then.

[JeffBezanson]

I don't get it --- is this another one of those unix things that just inexplicably doesn't work?

[rickhg12hs]

Ref: #7563
This also needs to be fixed for isreadable and isexecutable.

[vtjnash]

PR was #7418 for Isiah's attempt (since github only seems to have linked the commit sha1 from here)

I think we should just delete this functions. Since, as the man page says: "Warning: Using access() to check if a user is authorized to, for example, open a file before actually doing so using open(2) creates a security hole, because the user might exploit the short time interval between checking and opening the file to manipulate it"