HI !
That link leads to site where everything is quite old.
But I think I am able to resolve this. Compile of bindings is now running. Seems to take some time.
Problem is this(quete my first message):
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Assume it is because of bindings. Wiki says:
Bindings sources are located in lcl/interfaces/qt5/cbindings , to build it just follow README.txt.
Found them from /usr/lib64/lazarus/lcl/interfaces/qt5/
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Yep found them and there is readme.txt that says
download libqt5pas.soBut now I spent more time to study the folder structure and there is
another readme.txt under /cbindings.
Actually just what the wiki says!
And that readme has totally different content !!
Why, why, why they cannot be equal! Or at least the higer level readme should say that if you can not find ready made libqt5pas.so dive into subdir cbindings and see readme.txt there.
Now when you navigate to directory structure like this and you get into qt5 and find readme.txt you assume that is the one that tells all, but nope !!
My fault not to search every subdir, or read a little better the wiki !
But nice to see that no one else could not advise me too dive into subdir cbindings and look a bit more carefully !!
And another addition to cbindings/readme.txt would be that mentioned "qmake" command is "qmake-qt5" when using Fedora releases.
While writing this "make" finished and then I made "make install".
Next step was to open my program in lazatus. QT5 is there selected allready and make buld.
Now it went through without linking error.
Other quesiton is how it works, but that is another subject.
So, for use QT5 with program (in Fedora26 x86_64):
-goto project properties and select LCL widgetset "qt5"
-navigate to /lib64/lazarus/lcl/interfaces/qt5/cbindings/
(note ordinary user does not have write rights there, use sudo in front of commands, or copy directory cbindings (with subdirs) to user's folders. Then you need sudo just for "make install")
-issue command: qmake-qt5 -query
-issue command: qmake-qt5
-issue command: make (takes quite long time, just wait...)
-issue command :make install
Go back to Lazarus and issue "biuld".
After that start debugging your previously gtk written program.
Maybe later recompile lazarus to use qt5.