Bug#670756: Tuxguitar does not start

[Jakub Adam]

Hi Tony,

On 16.5.2012 17:01, tony mancill wrote:
> In any event, I'm still able to run tuxguitar on sid with both 3.5 and 3
> packages installed, so I'm not convinced we've ironed out the precise
> cause of the bug.

Ok, I will try to describe it more thoroughly:

The direct cause of crash is that required JNI library libswt-cairo-gtk-3555.so
(from package libswt-cairo-gtk-3.5-jni) is not installed when it has to be.

On a clean system where neither SWT nor tuxguitar is installed we can get into
this situation with following sequence of events:

(1) Install tuxguitar:

   $ apt-get install tuxguitar
   Reading package lists... Done
   Building dependency tree
   Reading state information... Done
   The following extra packages will be installed:
     libswt-cairo-gtk-3-jni libswt-gtk-3-java
   Suggested packages:
     libswt-gtk-3-java-gcj tuxguitar-jsa lilypond
   Recommended packages:
     tuxguitar-alsa tuxguitar-oss
   The following NEW packages will be installed:
     libswt-cairo-gtk-3-jni libswt-gtk-3-java tuxguitar
   0 upgraded, 3 newly installed, 0 to remove and 15 not upgraded.
   ...
   Setting up libswt-gtk-3-java (3.7.2-2) ...
   update-alternatives: using /usr/share/java/swt-gtk-3.7.jar to provide /usr/share/java/swt.jar (swt.jar) in auto mode.
   ...

   Now we have libswt-gtk-3-java, libswt-cairo-gtk-3-jni and /usr/share/java/swt.jar
   is provided by swt-gtk-3.7.jar. So far good, we can successfully launch tuxguitar
   and it will use SWT 3.7

(2) Now let's add libswt-gtk-3.5-java to the installation

   $ apt-get install libswt-gtk-3.5-java
   Reading package lists... Done
   Building dependency tree
   Reading state information... Done
   The following extra packages will be installed:
     libswt-gtk-3.5-jni
   Suggested packages:
     libswt-gtk-3.5-java-gcj libswt-gnome-gtk-3.5-jni
   The following NEW packages will be installed:
     libswt-gtk-3.5-java libswt-gtk-3.5-jni
   0 upgraded, 2 newly installed, 0 to remove and 15 not upgraded.
   ...

   We have libswt-gtk-3.5-java installed, *BUT NOT* libswt-cairo-gtk-3.5-jni and
   /usr/share/java/swt.jar is symlinked to swt-gtk-3.5.1.jar. When you now try to
   start tuxguitar, it will use SWT 3.5 and crashes with exception we already know
   from Grant:

   Exception in thread "main" org.eclipse.swt.SWTException: Unable to load graphics library [Cairo is required]
   (java.lang.UnsatisfiedLinkError: no swt-cairo-gtk-3555 or swt-cairo-gtk in swt.library.path, java.library.path
   or the jar file)

(3) To fix this, we can manually install libswt-cairo-gtk-3.5-jni. Then tuxguitar
finally runs also with SWT 3.5 - this is most probably your (Tony's) situation,
when you have both SWTs and application is working:

||/ Name                        Version                     Description
+++-===========================-===========================-====================================================
ii  libswt-cairo-gtk-3-jni      3.7.2-2                     Standard Widget Toolkit for GTK+ Cairo JNI library
ii  libswt-cairo-gtk-3.5-jni    3.5.1-2.1                   Standard Widget Toolkit for GTK+ Cairo JNI library
un  libswt-gnome-gtk-3-jni      <none>                      (no description available)
un  libswt-gnome-gtk-3.5-jni    <none>                      (no description available)
ii  libswt-gtk-3-java           3.7.2-2                     Standard Widget Toolkit for GTK+ Java library
un  libswt-gtk-3-java-gcj       <none>                      (no description available)
ii  libswt-gtk-3-jni            3.7.2-2                     Standard Widget Toolkit for GTK+ JNI library
ii  libswt-gtk-3.5-java         3.5.1-2.1                   Standard Widget Toolkit for GTK+ Java library
un  libswt-gtk-3.5-java-gcj     <none>                      (no description available)
ii  libswt-gtk-3.5-jni          3.5.1-2.1                   Standard Widget Toolkit for GTK+ JNI library
ii  libswt-webkit-gtk-3-jni     3.7.2-2                     Standard Widget Toolkit for GTK+ WebKit JNI library

It's that tuxguitar sometimes needs libswt-cairo-gtk-3.5-jni, but it's
not depending on it in any way.

Do you see where is the problem now or did I confuse you even more? :)

>> So I think we would have to change its Depends to something like:
>>
>>    Depends: libswt-gtk-3-java | libswt-gtk-3.5-java,
>>             libswt-cairo-gtk-3-jni | libswt-cairo-gtk-3.5-jni,
>>             ... etc
>>
>
> That change to depends won't have the desired effect.  All that
> expresses is "either libswt-gtk-3-java or libswt-gtk-3.5-java or both"
> which is what we are trying to avoid.  I believe you want to express an
> exclusive (XOR) in there - one or other, but not both.

You are right, my change is not sufficient. XOR might work, but I'm not
sure if this can be expressed in Depends.

> When you say "get rid of the alternatives," I'm not sure what you mean.
>   Tuxguitar only lists the following swt dependencies:
> libswt-gtk-3-java, libswt-cairo-gtk-3-jni, and libswt-webkit-gtk-3-jni.
>   It sounds like we might be back to conflicting with libswt-gtk-3.5-java.

I mean Niels' suggestion to remove old SWT packages, from one of previous mails:

On 15.5.2012 07:52, Niels Thykier wrote:
> Personally, I think the swt alternatives is... "weird" at best.  So I
> would vote for breaking the old packages to force their removal and then
> remove the usage of alternatives in Wheezy+1.
>    I think the original idea was to allow co-installation of two
> (API/ABI) incompatiable swt jars to smoothing transitions - however they
> are not going to enabled at the same time, so we would end up breaking
> some programs during a transition anyway.

In this scenario libswt-gtk-3-java will conflict with libswt-gtk-3.5-java
and other old SWT packages, so that situations in (2) and (3) will never
occur. Here, no change to tuxguitar package is needed.

Regards,

Jakub