Fix segfault when adding a layer

[pblottiere]

Fixes a segmentation fault happening when I try to add a vector layer on Archlinux.

The string returned by sqlite3_mprintf has to be freed.

[pblottiere]

@rduivenvoorde I think you've the same issue (cf https://lists.osgeo.org/pipermail/qgis-developer/2020-June/061421.html).

[rduivenvoorde]

Will build and test it

[rduivenvoorde]

Seems to work with me, no more segfault on opening vector data dialog.
I did have to clean first though.

[pblottiere]

Seems to work with me, no more segfault on opening vector data dialog.

Good. Thanks for testing @rduivenvoorde 👍

[3nids]

@pblottiere as mentionned in the commit, I am getting a crash on mac os.
Reverting this fixes the crash...
see 07eca3e#r39692642

[pblottiere]

Hi @3nids,

Mmmm... So if we use sqlite3_mprintf, we have a crash on Debian (and probably other Debian based distrib like Ubuntu) and at least Archlinux. But if we use QgsSqlite3Mprintf, we have a crash on mac os.

But QgsSqlite3Mprintf is used everywhere in QGIS source code instead of sqlite3_mprintf, so I don't think there's an issue with QgsSqlite3Mprintf itself...

A stupid idea: can you try to use a fresh QString for the second call to QgsSqlite3Mprintf instead of reusing sql?

[3nids]

A stupid idea: can you try to use a fresh QString for the second call to QgsSqlite3Mprintf instead of reusing sql?

no it doesn't help. Also, the crash happens within the call of QgsSqlite3Mprintf.

Shall we do an #ifdef on the OS?