glib warning in font_factory::GetUIStyles ("g_convert: assertion 'str != NULL' failed")

[Patrick Storz]

When launching Inkscape 0.92.x a lot of warnings are printed on the console:
  (inkscape.exe:4780): GLib-CRITICAL **: g_convert: assertion 'str != NULL' failed

This was reproduced in a 32-bit build of Inkscape 0.92.2pre0 (51816a8f55, 2017-07-26) but not a 64-bit build of the same version (both MSYS2 builds). Current master does not seem to be affected either.

gdb backtrace (with "set env G_DEBUG=fatal-criticals"; find attached) suggests this is happening in "font_factory::GetUIStyles()" in src/libnrtype/FontFactory.cpp.

Closer inspections shows that the error occurs when calling "familyUIName.compare( "sans-serif" )" and the four other similar statements, as "familyUIName" seems to contain invalid UTF-8 in this case.

The 64-bit build does not seem to reach these statements at all (as determined by appropriate debug statements).

[Patrick Storz (ede123)]

> The 64-bit build does not seem to reach these statements at all

Strike that part - the statement is reached but with a valid familyUIName.

[Patrick Storz (ede123)]

Issue further tracked down to "sp_font_description_get_family()".

While the 64-bit version correctly assigns the family name "sans-serif" if "pango_font_description_get_family()" returns "Sans", the 32-bit version produces garbled output (i.e. likely some invalid memory address)

[Patrick Storz (ede123)]

I was able to track down the source and it turns out a fix by Tavmjong committed to master only a week ago actually fixes this issue, too.

See https://gitlab.com/inkscape/inkscape/merge_requests/53

[Patrick Storz (ede123)]

Fixed in 0.92.x in
https://gitlab.com/inkscape/inkscape/commit/87435911a78ffac1d7bc33fe797f1d6782215016