FYI: Re: Qt 4.8 QUrl.toLocalFile behavior change, impacts to KUrl (and friends)

[Bart Cerneels]

We should build with QURL_NO_CAST_FROM_QSTRING in the 2.6 cycle to make sure
amarok works correctly with Qt 4.8.

On Thu, Oct 27, 2011 at 23:35, Thiago Macieira <thiago at kde.org> wrote:
> On Thursday, 27 de October de 2011 23:17:49 Milian Wolff wrote:
>> On Thursday 27 October 2011 21:11:11 Thiago Macieira wrote:
>> > On Thursday, 27 de October de 2011 13:32:51 Rex Dieter wrote:
>> > > See also,
>> > > http://bugs.kde.org/285028
>> > > ( and https://bugreports.qt.nokia.com/browse/QTBUG-22382 )
>> > >
>> > > In Qt 4.8, QUrl.toLocalFile now seems, by design, to return NULL for
>> > > urls
>> > > lacking any scheme.  Discovered this the hard way figuring out why all
>> > > my
>> > > audio knotifications were quiet.  Since audio event sources are simple
>> > > filenames, e.g. KDE-K3B-Finish-Success.ogg, and
>> > > QString soundFile = soundFileURL.toLocalFile();
>> > > no longer works.
>> > >
>> > > Any suggestions or advice on how best to deal with this?
>> >
>> > As we discussed on IRC, any string source must be properly labelled
>> > whether
>> > they are a URL or they are a local file. They cannot be both.
>>
>> is there at least a qWarning emitted in such a case, so we can find these
>> problems with QT_FATAL_WARNINGS=1 ?
>
> No, but there's something better:
>
> #define QURL_NO_CAST_FROM_QSTRING
>
> Your code will not compile when you're auto-casting. You'll need to select
> what to do:
>
>        QUrl::fromEncoded() - if it's a URL, with the "file" scheme
>        QUrl::fromLocalFile() - if it's a file name
>
> This option remains in Qt 5, but there there's going to be a new method to
> convert from QString to QUrl without passing through QByteArray.
>
> This is extremely important to get right because a filename and a URL are NOT
> the same. Certain characters in the string are interpreted differently
> depending on what the string is: %, # and ? in particular.
>
> So, to be honest, the bug *already* *existed* in your code if you're finding
> these problems now. I just made it blatantly clear, and it's been there for a
> year for people to see.
>
> I'm also calling right now KUrl's fromPathOrUrl a fatally flawed design.
>
> --
> Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
>   Software Architect - Intel Open Source Technology Center
>      PGP/GPG: 0x6EF45358; fingerprint:
>      E067 918B B660 DBD1 105C  966C 33F5 F005 6EF4 5358
>