INX: hidden parameter inside a notebook page triggers crash

[su_v]

INX files support hidden parameters (not shown in the GUI) using the attribute 'gui-hidden' for <param>.

Example:
<param gui-hidden="true" name="hidden_opt" type="boolean">true</param>

This works fine as long as the parameter is defined in the root level of <inkscape-extension>, but causes Inkscape to crash when creating the dialog based on the INX file if is is inside a notebook page:

  <param name="tab" type="notebook">
    <!-- tab1 -->
    <page name="first_tab" _gui-text="First">
      <!-- hidden param doesn't work here -->
      <param gui-hidden="true" name="hidden_inside_tab_opt" type="boolean">false</param>
      <!-- normal param is ok -->
      <param name="instructions" type="description" xml:space="preserve">Text on first tab.</param>
    </page>

None of Inkscape's own extensions tries to use a hidden parameter this way. I only came across this while working on a custom extension where I would have liked to group hidden parameters with visible parameters per tab (code-wise this is not strictly necessary, but it may help keep an INX file better "organized").

Crash (current trunk r11952 on OS X 10.7.4):
Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x0000000000000000
0x00000001037003eb in Gtk::Box::pack_start ()

[su_v (suv-lp)]

attaching archive with two extensions demonstrating the reported issue.

[jazzynico (jazzynico)]

Confirmed on Windows XP, Inkscape trunk revision 11951.

Since gui-hidden is a valid attribute (even in a tab), we can consider it a bug.
Importance lowered (in accordance with http://wiki.inkscape.org/wiki/index.php/Bug_management#Bug_importance) compared to a usual crash.

[jazzynico (jazzynico)]

Patch tested (very quickly) on Windows XP, Inkscape trunk revision 11951.
The demo file from comment #2 now works as expected.
No regression found so far, but since it is just a missing test on the existence of the widget (NULL when gui-hidden is set), the risk is quite low.

[jazzynico (jazzynico)]

Fix committed in the trunk, revision 11956.

[su_v (suv-lp)]

@JazzyNico - thx :) (it tested ok on OS X too - sorry for the delayed response!)

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