Mac OS X tcltk/X11 issues

John talked to me about this a month ago and after some sick
leave/vacation I had just got around to thinking into it.

Minor points:

1) The usual way to check for OS X in the R sources is
grepl("darwin", R.version$os)

2) It is perfectly possible to build R on Linuxen without X11
headers/libraries.

3) There are three branches to the Tk code, X11, Aqua and Windows.  So
apart from on Windows and OS X you either use X11 or do not have Tk.

4) It is possible to build R without Tcl/Tk, in which case you get a
stub tcltk package.  Then capabilities('tcltk') tells you that you have
the stub.

5) Just so we are all understand, it is possible (and documented in the
manuals) for tcltk to be built using the Aqua Tk branch, and then Rcmdr
works well (in my opinion much better) without X11 present.  So we do
not want Rcmdr checking unconditionally for X11 being present.


My understanding is that the main problem is that if someone installs
one of the CRAN binary packages for OS X and does not have X11 installed
then library(tcltk) will fail with a message that they do not
understand, e.g.
https://stat.ethz.ch/pipermail/r-sig-mac/2014-July/010954.html .

For the future, probably the best thing to do is for the tcltk startup
code to try to trap that case and suggest that X11/XQuartz needs to be
installed.  The problem is accurately identifying 'that case'.

If a package has tcltk in the imports of its NAMESPACE, there is nothing
it can do about a broken tcltk as the namespaces it imports will be
processed before any of the code in the package.  So the other
possibility is to not have tcltk in the imports but to load its
namespace via Rcmd::.onLoad.  I figured out how to to do that but it
would be rather fragile.


There is another possible problem which is that X11 is installed but a X
server is not running.  That's what capabilities('X11') checks, and on
modern OS X it ought to launch the X server as required.  However, I do
not think we have a way to telling which Tk branch package tcltk was
built against.  Since that is only an issue on OS X (no other OS can use
more than one branch) you could use something like

Tk_is_X11 <- function()
{
     DLL <- system.file("libs", "tcltk.so", package = "tcltk")
     out <- system2("otool", c("-L", shQuote(DLL)), stdout = TRUE)
     length(grep("libX11[.][0-9]+[.]dylib", out)) > 0L
}

and then

if (.Platform$OS.type == "unix") {
    if (!grepl("darwin", R.version$os) || Tk_is_X11())
        if(!capabilities("X11"))
             stop("Rcmdr requires a running X server")
}


On 15/07/2014 13:05, Marc Schwartz wrote:

John,

First, apologies for my narrow focus on the solutions that I proposed
yesterday. I suffered from tunnel vision on the OS X issue and as
Gabor has noted, it would not be sufficiently portable. There can be
potential variations on where X11 is installed on OS X, depending upon
the use of Xquartz, the original Apple distribution of X11 and
presumably could further vary if one installs from source, is using
Homebrew, Macports or similar, which are package management systems
for OS X. Thus, as Gabor pointed out, capabilities("X11") is the most
portable approach.

With respect to Linux, to the best of my knowledge, X11 (for some time
X.org) is still a requirement for tk (but not tcl). In checking at
least the current Fedora repos, X11 is still listed as a dependency
for tk. So if one is using the common package management systems, X11
will be installed if not already, when installing tk, unless one
overrides the defaults.

Also, at least for Fedora and perhaps other Linuxen, X11 is listed as
a dependency for R itself, so if one is installing R on Fedora, X11
will be installed as well, if not present.

Thus, between the common Linux package management systems and that
Linux users tend to be more technically saavy, you do not see many
reports.

You likely already know this, but you could utilize a more generic
approach to testing the platform by using:

   if (.Platform$OS.type == "unix")
     ...

which would cover Linuxen, Unixen and OS X and then run your X11
checks, secondarily perhaps testing for OS X, if you wish to give a
more specific error message for OS X users and point them to XQuartz.

Regards,

Marc



On Jul 14, 2014, at 11:37 PM, John Fox <jfox at mcmaster.ca> wrote:

Hi Gabor,

Thanks for the clarification.

I agree that it would be best to intercept the problem on Linux/Unix
as well as on Mac OS X. Do you know that X11 is necessary for the
tcltk package to work on Linux/Unix systems (or is there possibly a
non-X11 Tcl/Tk there that's compatible with the tcltk package)?

As a practical matter, the problem occurs with some regularity on Mac
OS X (I'm aware that the availability and default installation of X11
varies by version of the OS), but I've not seen a report of it on
Linux, so my immediate concern was to solve the problem on Mac OS X.

Best,
John

On Mon, 14 Jul 2014 21:37:54 -0400
G?bor Cs?rdi <csardi.gabor at gmail.com> wrote:

Hi John,

On Mon, Jul 14, 2014 at 8:12 PM, John Fox <jfox at mcmaster.ca> wrote:

Dear Gabor,

As I just explained, the problem isn't testing for X11, which I
know how to do -- though capabilities("X11") is a bit better than
what I suggested. The issue is specific to Mac OS X because the
Windows implementation of R includes a Tcl/Tk that doesn't use X11,
and I've never seen the problem on Linux.

actually, what I am saying is, that it is not specific to OSX. Some
(older, before 2012) OSX versions do include an X11 server, and some
Linux or other Unix installations do not.

I am not saying tcltk should not test for an X11 server, all I am
saying is that the test suggested below (based on the os and the
existence of a certain file) is not the best one.

If it turns out that there is no X11 server, and the os is OSX, then
indeed a dialog box could be displayed, see e.g. the one at
http://www.macrumors.com/2012/02/17/apple-removes-x11-in-os-x-mountain-lion-shifts-support-to-open-source-xquartz/


Best,
Gabor

Best,
John

-----Original Message-----
From: G?bor Cs?rdi [mailto:csardi.gabor at gmail.com]
Sent: Monday, July 14, 2014 6:37 PM
To: Marc Schwartz
Cc: John Fox; urbanek at research.att.com; R-SIG-Mac
Subject: Re: [R-SIG-Mac] Mac OS X tcltk/X11 issues

What's wrong with capabilities("X11")?

I am not sure if teting for the OS, and especially for a particular X
server, installed in a particular directory, is a good idea, even if
it covers most of the _current_ installations.

Gabor

On Mon, Jul 14, 2014 at 6:13 PM, Marc Schwartz <marc_schwartz at me.com>
wrote:

On Jul 14, 2014, at 4:53 PM, Marc Schwartz <marc_schwartz at me.com>

wrote:

On Jul 14, 2014, at 4:13 PM, John Fox <jfox at mcmaster.ca> wrote:

Dear Simon and list members,

As many of you are aware, when X11 isn't installed on Mac OS X,

loading the

tcltk package produces an error, with a message that many users

find

cryptic. There was yet another instance of this problem
reported to

the list

today.

I'm interested in the issue because the Rcmdr package uses tcltk

and thus

fails to load when X11 is absent. Rcmdr users tend to be

inexperienced and

so, unless they find their way to the Rcmdr installation webpage,

where

detailed installation instructions are provided, they tend to be

stymied by

the problem.

If I could, I'd intercept the problem by checking

capabilities()["X11"] in

the Rcmdr .onLoad() or .onAttach() function, but because the Rcmdr

package

imports the tcltk namespace, the error occurs before these startup

functions

are executed -- a chicken-and-egg problem.

It occurs to me that tcltk could fail more gracefully on Mac OS X

when X11

is absent, perhaps popping up a webpage in a browser with

instructions and a

link for installing XQuartz. I'd do this myself in the Rcmdr

package if I

could. Or tcltk could check for the presence of X11 and not try to

start it

if it's absent, reporting a warning rather than throwing an error.

Alternatively, I'd be grateful if someone could suggest how I
might

detect

the problem in the Rcmdr package before loading fails. The only

thing that I

could think of was writing a separate RcmdrInstall package that

bypasses

tcltk, but that would be awkward and would only help users who

discovered

that RcmdrInstall exists.

Thanks,
John

John,

Is there someplace in your startup process where you could run code

along the lines of:

if (grepl("apple", R.version$platform) &

length(list.files("/opt/X11/bin", pattern = "Xquartz")) == 0) {

    cat("X11 is required. Please visit
http://xquartz.macosforge.org

to download and install Xquartz.")

    stop()
}


The above code will check to see if the user is running R on OS X

and also if the Xquartz binary is present in the default location.

Not sure if this is helpful.

A possible correction in the above code relative to detecting OS X:

if ((Sys.info()["sysname"] == "Darwin") &

length(list.files("/opt/X11/bin", pattern = "Xquartz")) == 0) {

    cat("X11 is required. Please visit http://xquartz.macosforge.org

to download and install Xquartz.")

    stop()
}


I believe that Sys.info()["sysname"] == "Darwin" is preferred for

detecting the OS that R is running on versus the OS that it was built
upon according to the help files, if I read correctly. This could be
important if someone is building R from source versus installing
Simon's CRAN binary, I presume.

Regards,

Marc