<Swing Dev> Review request for 8013566: Failure of GroupLayout in combination of addPreferredGap and addGroup's

[Semyon Sadetsky]

Hi,

please review a fix for JDK9.

bug: https://bugs.openjdk.java.net/browse/JDK-8013566
webrev: 
http://cr.openjdk.java.net/~alexsch/semyon-sadetsky/8013566/webrev.00/

User got here an infinite loop inside GroupLayout's auto-gap-insertion 
mechanism that was triggered by getPreferredSize() call upon the 
JFrame.pack().
The GroupLayout has not trivial algorithm and its code is really 
nontransparent. The aim of its auto-preferred-gap-insertion algorithm is 
inserting gaps between the container components. This allows user to not 
specify gaps manually for convenience.
In the considered scenario user relays on the 
auto-preferred-gap-insertion except for one place where he specifies the 
preferred gap manually. Moreover this manual preferred gap is inserted 
not at the leading position but at the trail. That is specifically the 
case when the algorithm fails.

The thing is that the auto-preferred-gap-insertion routine 
insertAutopadding() cannot distinguish its auto inserted preferred gaps 
from manual preferred gaps because it uses the "instance of" check but 
all those gaps are instances of the same AutoPreferredGapSpring class. 
Also the insertAutopadding() does not insert gaps at trailing positions 
but only at leading.  More precisely the trailing AutoPreferredGapSpring 
object left from the child level group (which insertAutopadding() is 
called recursively) is ignored on the parent group level and parent's 
insertAutopadding() inserts a new leading AutoPreferredGapSpring object 
connected to the last component of the child level group, but this in 
its turn makes a spring counter value (which serves as a loop exit flag) 
incorrect. As result preferred gaps are added infinitely on this position.
The fix introduces a check that tests if the AutoPreferredGapSpring 
related the current leading component is already created as a trailing 
gap on the child group level, and if it is this trailing 
AutoPreferredGapSpring is used to setup the source and new 
AutoPreferredGapSpring object is not created.

--Semyon


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