<Swing Dev> RFR: 8247753: UIManager.getSytemLookAndFeelClassName() returns wrong value on Fedora 32

[Pankaj Bansal]

Hi All,

Please review the following fix for jdk16.

Bug : https://bugs.openjdk.java.net/browse/JDK-8247753
webrev: http://cr.openjdk.java.net/~pbansal/8247753/webrev00 
<http://cr.openjdk.java.net/%7Epbansal/8247753/webrev00>

Bug: UIManager.getSytemLookAndFeelClassName() returns wrong value on 
Fedora 32. It is returning the MetalLookAndFeel classname instead of 
GTKLookAndFeel classname.

Cause: Java uses a environment variable GNOME_DESKTOP_SESSION_ID to 
verify if the system is gnome (which is set by gnome) and then checks 
for GTKLookAndFeel support. If both conditions are satisfied, then 
GTKLookAndFeel classname is returned, else cross platform 
MetalLookAndFeel is selected.

The GNOME_DESKTOP_SESSION_ID environment has been |deprecated| for a 
long time and the value is set to "|this-is-deprecated|" by gnome. In 
java, the actual value of variable is not being verified. As long as the 
value is not null (it has been set to something by gnome), things have 
been working fine though the value  set by gnome is 
"|this-is-deprecated|". Now, gnome has removed the variable completely 
and this is causing issues in Fedora 32. As the variable is not set at 
all, java is returning the cross platform MetalLookAndFeel classname for 
the SystemLookAndFeelClassName instead of GTKLookAndFeel.

More information on this in JBS. Right now the issue is seen only on 
Fedora 32, but this can very well come in future releases of RHEL, 
CentOS, Oracle Linux etc.

Fix: We should check XDG_CURRENT_DESKTOP also along with 
GNOME_DESKTOP_SESSION_ID to verify gnome based linux. 
XDG_CURRENT_DESKTOP is set by gnome based platforms to some string 
containing "gnome" substring. So, this can be used to verify the gnome 
based desktop. For backward compatibility, we need to continue checking 
GNOME_DESKTOP_SESSION_ID as well because for some linux platforms, 
XDG_CURRENT_DESKTOP may be set to something else as they are not gnome 
based, but have been returning GTKL&F as GNOME_DESKTOP_SESSION_ID was 
set by them. so, we dont want to change anything for them.

Other solution could have been to just make GTKL&F default on all linux, 
but that would result in GTKL&F being selected on some new platfoms like 
KDE based platforms where currently Metal L&F is selected.

I have modified the test case 
test/jdk/javax/swing/LookAndFeel/SystemLookAndFeel/SystemLookAndFeelTest.java. 
The test fails on Fedora 32 without fix and passes with the fix. I have 
run the required mach5 tests and this fix is not breaking anything. Link 
in JBS.


Regards,

Pankaj Bansal

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