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

[Jorge Gustavo Rocha]

+1 to delay this breaking change or to follow a Denis' approach :-)

Jorge

Às 13:28 de 12/06/25, Denis Rouzaud via QGIS-Developer escreveu:
> 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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