[Development] Proposal to raise the minimum CMake version needed to build and use Qt 6.9

[Alexandru Croitor]

Hi,

> On 14. Nov 2024, at 09:25, Bogdan Vatra <bogdan.vatra at kdab.com> wrote:
> 
> Hi,
> 
>  Just out of curiosity, what are the features added to cmake 3.26 that makes 
> it so much better than 3.25 and which Qt really needs?


You can see my findings at 
https://bugreports.qt.io/browse/QTBUG-131169?focusedId=841296&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-841296

For 3.26, the most important thing would be the $<BUILD_LOCAL_INTERFACE:...> genex.

I expect its usage will help in certain scenarios which allow using a newer CMake feature during the qt build, but still making the resulting Qt packages compatible with an older CMake version.

This would affect public api.

One case like that recently appeared in https://codereview.qt-project.org/c/qt/qtbase/+/601486/11/cmake/QtPublicPluginHelpers.cmake#514