[QGIS-Developer] QGIS 3.44 projects compatibility with previous versions

[Denis Rouzaud]

just thinking that it will probably give the same error message!
so maybe a v2 like:

<properties>
  <foo>
    <bar type="QString">baz</bar>
  </foo>
</properties>
<properties-v2>
  <properties name="foo">
    <properties name="bar" type="QString">baz</properties>
  </properties>
</properties-v2>

Le jeu. 12 juin 2025 à 14:28, Denis Rouzaud <denis.rouzaud at gmail.com> a
écrit :

> Hi,
>
> I did something similar in the symbology area and I went for saving twice
> the data.
> We could probably leave the two at the same time in the same tag:
>
> <properties>
>   <foo>
>     <bar type="QString">baz</bar>
>   </foo>
>   <properties name="foo">
>     <properties name="bar" type="QString">baz</properties>
>   </properties>
> </properties>
>
> Old QGIS would only save the old, new QGIS would save both and use the new
> if it exists.
>
> Best of the 2 worlds?
>
> Cheers,
> Denis
>
>
>
> Le jeu. 12 juin 2025 à 13:55, Stefanos Natsis via QGIS-Developer <
> qgis-developer at lists.osgeo.org> a écrit :
>
>> Hi list
>>
>> During the last dev cycle, a change was introduced in the way that
>> properties are stored in the .qgs xml file
>> https://github.com/qgis/QGIS/pull/60855
>>
>> While this solved a real issue (data-driven properties could result in an
>> invalid property name with a leading digit) in an elegant way and is
>> technically backwards compatible (projects generated with older versions
>> can be opened without issues), it has the side effect that projects stored
>> with 3.44 will not properly load in older QGIS versions (stored properties
>> are ignored and also project CRS is undefined). Plugins could also
>> malfunction as they often use project properties for storing their
>> project-related configurations.
>>
>> One potential solution would be to backport this to LTR, however from my
>> experience a good percentage of the users use older QGIS versions and even
>> those on LTR do not always upgrade as soon as a new release is out, so
>> backporting could eventually make things worse!
>>
>> With QGIS 4.0 around the corner, imho, it would be better to defer this
>> change for a couple more months and only include this kind-of-breaking
>> change in QGIS 4.0
>>
>> I briefly chatted with Jurgen at the hackfest about this and while
>> acknowledging the issue, was not super happy to revert, so I'm interested
>> in gathering more opinions here.
>>
>> Best
>> Stefanos
>>
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