Qt 6 To Begin Early Stages Of Development In Git

While Qt 6.0 isn't due out for the better part of two years still, early patches planned for Qt 6 are expected to begin taking shape within a Git staging branch.

Lars Knoll laid out plans today to have a Qt 6 branch start for qtbase, since that's where most of the early stage Qt6 development will begin taking place. Already he's been collecting some patches from fellow developers and at least having this branch early will serve as a basis for staging until the Qt 6.0 development really heats up.

The current Qt5 "dev" code would regularly merge into the Qt6 code-base, functions planned for removal in Qt6 would need to be first marked as deprecated by the Qt5 code, and binary compatibility breakage can begin.

The most recent Qt 6 plans call for its inaugural release in November 2020. Qt 5.15 LTS is expected to be the last of the line for Qt5.

Qt6 will likely settle on a C++17 base, has been focusing upon CMake as its preferred build system (after originally investing in Qbs), and this initial 6.0 release will likely focus on restructuring/deprecating/cleaning as opposed to delivering jaw-dropping new features. Their goal is for the Qt5 to Qt6 transition being smooth for both developers and end-users.

With the Qt development mailing list archives being broken, below is the message Lars had to say about the Qt6 Git branch plans:

I’d like to have us create a branch for Qt 6 in qtbase. Different people are starting to collect quite some patches and we now need one place where those come together.

For now I’d like to limit this to qtbase, as that’s where pretty much all Qt 6 related work happens, and we need to do some work on the CI side to prepare the other modules for Qt 6 related work (Frederik will post details in a separate mail).

The branch can have limited testing where we compile and test against latest compilers on Windows, macOS and Linux only.

For now the following rules would apply to the ‘qt6’ branch:

* We regularly merge dev into it
* BC breakages are fine
* SC breakages require a maintainer approval and a Changelog entry marking this as a source incompatible change
* All functions you’d like to remove in qt6 need to be deprecated in dev first
* Avoid changes to the build system to not interfere with the cmake work

I’d like to see the cmake changes being merged into the branch as soon as possible, and have us switch over soon.