Qt5 5.6 regression: conversion from QVariant to QString is broken

[Mathieu Pellerin]

A regression was introduced in Qt5 5.5 - fixed in 5.7 - whereas conversion from QVariant to QString is broken for double and float values (you can see more details on this here: https://bugreports.qt.io/browse/QTBUG-47192).

The patch fixing this issue is the following: http://code.qt.io/cgit/qt/qtbase.git/patch/src/corelib/tools/qlocale.h?id=726fed0d67013cbfac7921d3d4613ca83406fb0f

Would it be possible to apply this patch against the package (based on Qt5 5.6.1) Ubuntu 16.10 will ship in October? It's a pretty ugly bug, which needs addressing. Hopefully the Qt devs can eventually merge this patch onto their 5.6 LTS branch.

[Mathieu Pellerin (nirvn-asia)]

Ok, while trying to create a debdiff (with the help of Simon Q on IRC, thanks :) ), I realized the above is effectively part 2, and part 1 is this commit:

Part 1: https://codereview.qt-project.org/#/c/127924/12//ALL,unified
Part 2: https://codereview.qt-project.org/#/c/127924/12//ALL,unified (same as the .patch link above)

This fixes QTBUG-44039, QTBUG-43885, and QTBUG-47192.

[Timo Jyrinki (timo-jyrinki)]

Thanks for the report and finding both of the commits!

[Timo Jyrinki (timo-jyrinki)]

I think you meant https://codereview.qt-project.org/#/c/104737/32/ for patch 1 :D

[Timo Jyrinki (timo-jyrinki)]

The patches do not apply to 5.6 as is, although it doesn't look too complicated failing.

[Mathieu Pellerin (nirvn-asia)]

Timo, yes sorry, you've got the proper link :)

[Timo Jyrinki (timo-jyrinki)]

Also https://codereview.qt-project.org/#/c/139057/ is needed. Next time, full debdiff with working and rebased patches please :)

[Timo Jyrinki (timo-jyrinki)]

Unfortunately fixing this would be causing true regressions in at least ktexteditor and pyqt5:

https://requests.ci-train.ubuntu.com/static/britney/landing-1920/yakkety/excuses.html

https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-yakkety-ci-train-ppa-service-landing-1920/yakkety/amd64/k/ktexteditor/20160914_111856@/log.gz
https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-yakkety-ci-train-ppa-service-landing-1920/yakkety/amd64/p/pyqt5/20160914_140056@/log.gz

I'm not sure if rebuilding qtxmlpatterns would be enough or what other kind of problems there could be lurking. Since 16.10 release is coming closer, I think the set of these three patches (that remove a symbol among else) is too risky. The fix would eventually be in Qt 5.7 in Ubuntu 17.04, unless of course a less invasive fix could be had for 16.10.