Crash when toggling guides after opening Document Properties from 'Duplicate Window'

[su_v]

Inkscape crashes when toggling visibility of guides after having opened 'Document Properties' dialog from a duplicate document window.

Steps to reproduce:
1) launch inkscape (default prefs, default new document)
2) open menu 'View > Duplicate Window'
3) open Document Properties (Shift+Ctrl+D) while focus is in duplicate window
4) close Document Properties (Ctrl+W)
5) close duplicate window (Ctrl+W)
6) toggle guides (click on ruler, or menu 'View > Guides')

--> crash:
Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x0000000000000030
SPDocument::getRoot (this=0x0) at document.h:129
129 SPRoot *getRoot() { return root; }

Crash was first noticed with Inkscape 0.91+devel r14267 on OS X 10.7.5.

Testing with stable releases and archived builds:
- not reproduced with Inkscape 0.48.5 r10040,
- not reproduced with Inkscape 0.48+devel rev <= 9944,
- reproduced with Inkscape 0.48+devel rev >= 9950,
- reproduced with Inkscape 0.91 r13725;
the cash is likely related to the changes of the C++ification merge in rev 9946:
https://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/changes/9950

Revision 9946: GSoC C++-ificiation merge and cleanup.
https://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/9946

Notes:
* backtraces with earlier trunk builds slightly differ from those with latest trunk
* Inkscape 0.48.5 and trunk builds older than r9944 produced console messages too but did not crash:
(inkscape-bin-9944:79884): GLib-GObject-WARNING **: invalid uninstantiatable type `(null)' in cast to `GtkWidget'

(inkscape-bin-9944:79884): GLib-GObject-WARNING **: invalid uninstantiatable type `(null)' in cast to `GObject'

(inkscape-bin-9944:79884): GLib-GObject-CRITICAL **: g_object_get_data: assertion `G_IS_OBJECT (object)' failed

** (inkscape-bin-9944:79884): CRITICAL **: gdouble sp_document_width(SPDocument*): assertion `document != NULL' failed

** (inkscape-bin-9944:79884): CRITICAL **: gdouble sp_document_height(SPDocument*): assertion `document != NULL' failed

** (inkscape-bin-9944:79884): CRITICAL **: gdouble sp_document_width(SPDocument*): assertion `document != NULL' failed

** (inkscape-bin-9944:79884): CRITICAL **: gdouble sp_document_height(SPDocument*): assertion `document != NULL' failed

[jazzynico (jazzynico)]

Also reproduced on Windows XP (32bit), Inkscape trunk rev. 14195.

[Nathan Lee (nathan.lee)]

Replicated 0.92.3 ppa, and Inkscape 1.1-dev (b1c77e6, 2020-01-24) appimage Linux Mint 19.1

Also replicated in b70353cad4a, fix introduced somewhere in https://gitlab.com/inkscape/inkscape/-/merge_requests/1325 (so the commits right after that), bisection points at d977fb1001f310ede5d60239955a898e18c5650d

(only looked at backtrace in 0.92.3 and Inkscape 1.1-dev (b1c77e6, 2020-01-24)).

Closing as fixed