QtCS2021 - Qt Buildsystem Feedback

Session Summary

• Qt 6 switched to using CMake for building Qt. The session is meant to gather feedback / pain points about building Qt as well as using Qt in a user project (from a build system perspective). General questions about build system usage are also welcome.

Session Owners

• Alexandru Croitor (alexandru.croitor@qt.io)

Notes

(Notes by alcroito)

Documentation links

• Building Qt
• https://doc.qt.io/qt-6/qt6-buildsystem.html
• https://doc.qt.io/qt-6/configure-options.html
• https://doc.qt.io/qt-6/build-sources.html
• https://wiki.qt.io/Qt_Build_System_Glossary

• Using Qt
• https://doc.qt.io/qt-6/cmake-manual.html
• https://doc.qt.io/qt-6/qmake-manual.html

Status update

• 99% of platforms and repositories ported
• Various improvements to CMake upstream
• New public CMake API for qml modules in 6.2
• New public CMake API plugin, executable, translation creation
• Still things to work on like unified deployment story, android multi-ABI, better docs

Feedback session

• Some positive feedback
• Some pain points still exist
• IDE integration can be improved (don't reconfigure, don't rebuild, don't clobber files when not needed)
• Sanitizer flags should propagate to applications like in qmake https://bugreports.qt.io/browse/QTBUG-92083
• Discussed if any issues can arise as part of qtquickcontrols2 -> qtdeclarative merge (qmlimportscanner issues in tests mostly)
• Request to add a new feature for a documentation toggle of CMake vs qmake code
• Request to document that one can build a test without having to build all of Qt
• Request to document how to get the command line that is used to run a specific test or test function
• qmake was easier to use for standard projects, but extremely hard for non-standard projects
• Positive feedback on providing a unified deployment story (non-official linuxdeployqt is a pain point) https://bugreports.qt.io/browse/QTBUG-74940
• No longer being able to open a Qt library and/or tests as self-contained projects in Qt Creator slows down development
  • At least test projects can be made standalone, needs some manual work https://bugreports.qt.io/browse/QTCREATORBUG-25389
  • Possibly distribute the work via @dev mailing list
• Question about if CMake allows to bundled macos / ios related data as qmake allowed to, can be done using https://cmake.org/cmake/help/latest/prop_tgt/MACOSX_BUNDLE_INFO_PLIST.html
• Documentation needs to be updated in many places to also include the cmake way of doing things: like in this post where it only shows the qmake addition but no cmake: https://doc-snapshots.qt.io/qt6-dev/qtqml-cppintegration-topic.html
  • This is being worked on as part of new QML CMake API documentation
• Request to add support for sanitizers when using MSVC
• Platform plugins are not built by default when building a test (this should be fixed though?)
• There seems to be a bit a dependency creep; some small changes in some obscure file seem to trigger a full rebuild of qtbase, this also propagates to Qt for Python
  • Needs thorough investigation
• Pointed out that CMake help can be received at https://discourse.cmake.org/

Poll

* 65% ish - Prefer cmake + ninja
* 5%  ish - Prefer qmake + make
* 10% ish - Both are fine
* 1%      - I wanted to choose something else
* Some people didn't answer