Qt6 + CMake migration #165

slipher · 2025-11-12T03:09:29Z

Requires the updater-wip branch from https://github.com/slipher/fluid.

There are two branches. This one, slipher/qt6, includes only the commits that are supposed to be related to Qt6 migration. The other one slipher/qt6-combined represents the actual working copy I am using which includes some other commits.

Upgrade from Qt 5.14 to 6.8; migrate from qmake to cmake; update Fluid by a lot which requires some migrations; also update Quazip which didn't require any migrations.

Current issues:

illwieckz · 2025-11-12T03:14:36Z

It now depends on libxcb-cursor.so.0 and I had to install libxcb-cursor0 on my end, meaning no one of the applications I use requires that, meaning that dependency is very rare.

Edit: I forgot to say I'm running Ubuntu 24.04.3 LTS Noble Numbat.

build-qt.sh

illwieckz · 2025-11-12T13:12:25Z

build-qt.sh

+    -DFEATURE_formlayout=OFF
+    -DFEATURE_fscompleter=OFF
+    -DFEATURE_future=OFF
+    -DFEATURE_gc_binaries=OFF


If this is the same as -gc-binaries, it should be ON to reduce size:

According to https://doc.qt.io/qt-6/build-optimized-qt.html:

-gc-binaries
Remove unnecessary parts from binary. Place each function or data item into its own section and enable linker garbage collection of unused sections.

Done. gc-binaries + reduce-exports shaved off 1.8M.

illwieckz · 2025-11-12T14:25:17Z

I get this:

In file included from /updater/downloadworker.cpp:20:
/updater/downloadworker.h:25:10: fatal error: QStandardItemModel: No such file or directory
   25 | #include <QStandardItemModel>
      |          ^~~~~~~~~~~~~~~~~~~~

slipher · 2025-11-12T14:57:27Z

I get this:

In file included from /updater/downloadworker.cpp:20:
/updater/downloadworker.h:25:10: fatal error: QStandardItemModel: No such file or directory
   25 | #include <QStandardItemModel>
      |          ^~~~~~~~~~~~~~~~~~~~

I guess the "remove an unused include" commit from slipher/qt6-combined is needed.

illwieckz · 2025-11-12T15:15:15Z

That was that, thanks!

illwieckz · 2025-11-12T15:30:40Z

Out of curiosity, I tried building Qt without OpenGL, to see if that would save space. The updater builds and runs this way but that looks ugly: curves are aliased, and some background color on configuration dialog is wrong.

illwieckz · 2025-11-12T15:46:07Z

It now depends on libxcb-cursor.so.0 and I had to install libxcb-cursor0 on my end, meaning no one of the applications I use requires that, meaning that dependency is very rare.

Edit: I forgot to say I'm running Ubuntu 24.04.3 LTS Noble Numbat.

That's annoying: when that dependency isn't there, Qt6 doesn't build, but we cannot ship an updater requiring it.

On Ubuntu 24.04 that dependency is not installed by default, and is required by only 8 softwares! That means no one have this dependency installed on Ubuntu LTS! Maybe we will have to build it statically.

slipher · 2025-11-12T16:05:01Z

Out of curiosity, I tried building Qt without OpenGL, to see if that would save space. The updater builds and runs this way but that looks ugly: curves are aliased, and some background color on configuration dialog is wrong.

The Qt Quick documentation says that some effects are expected not to display if software rendering is used. Also I get high CPU usage in that mode (for me it happens when I run the app from a container that lacks some support libs).

It now depends on libxcb-cursor.so.0 and I had to install libxcb-cursor0 on my end, meaning no one of the applications I use requires that, meaning that dependency is very rare.
Edit: I forgot to say I'm running Ubuntu 24.04.3 LTS Noble Numbat.

That's annoying: when that dependency isn't there, Qt6 doesn't build, but we cannot ship an updater requiring it.

On Ubuntu 24.04 that dependency is not installed by default, and is required by only 8 softwares! That means no one have this dependency installed on Ubuntu LTS! Maybe we will have to build it statically.

Ouch. It seems Qt 6 has the opposite problem of Qt 5, which had too few hard requirements and ended up not displaying properly on the initial attempt to upgrade to Bullseye. There is an extensive list of libs for the test named xcb_syslibs in the build system which are required all or nothing. But recently I saw somewhere an option for using an internal xcb that we should try out. I forgot what the option is called but I can see the code in there at qtbase src/3rdparty/xcb/.

slipher · 2025-11-14T02:31:49Z

I now have a version that statically links against the libxcb-XXX libraries from Debian.

illwieckz · 2025-11-14T02:39:05Z

Excellent!

illwieckz · 2025-11-14T02:52:30Z

Some minor changes that live in a local branch of mine:

The install command looks like this way on my end:

RUN apt-get update \
    && apt-get install -y \
    autoconf \
    autopoint \
    ca-certificates \
    curl \
    gettext \
    git \
    g++ \
    libgl1-mesa-dev \
    libtool \
    libx11-xcb-dev \
    libxcb-glx0-dev \
    libxkbcommon-x11-dev \
    make \
    ninja-build \
    perl \
    p7zip-full \
    pkg-config \
    python \
    xz-utils \
    zlib1g-dev \
    $XCB_MINIMUM_PACKAGES \
    && echo 'deb https://archive.debian.org/debian bullseye-backports main' > /etc/apt/sources.list.d/backports.list \
    && apt-get update \
    && apt-get install -y \
    cmake/bullseye-backports \
    && apt-get clean

It installs explicitely ca-certificates because that's needed for the archive depot. It worked before because a package pulled it (probably curl), but it's not bad to be explicit.
It runs apt-get clean at the end in hope the snapshotted docker step is smaller on disk.
The backport repository url is made a bit smaller.
Also, just as a style concern, I put the && at the beginning of the line so it makes more obvious to my eyes it's a command and not an argument.

I also have a patch that moves the Aria build before the Qt build, so anytime Qt changes are made, the whole build is faster because modifying the Qt build doesn't invalidate the Aria build because of ordering.

I had a third patch adding ENV LANG=C.UTF-8 before anything else, but you already implemented the same yourself.

illwieckz · 2025-11-14T03:27:13Z

I don't know if that's bad or not, but Qt links against libxcb-xkb.a while also linking against libxkbcommon-x11.so.0 which is linked against libxcb-xkb.so.1, meaning we link against two libxcb-xkb, and one of them will be the static one from the Debian docker, while the other one will be the shared one from the user's computer.

illwieckz · 2025-11-14T04:10:38Z

Doing this makes sure the shared lib is always used for xcb-xkb while others are linked statically:

RUN ls /usr/lib/x86_64-linux-gnu/libxcb-*.so | grep -v xcb-xkb | xargs rm -v

slipher · 2025-11-14T04:12:23Z

The input part is where Qt has a bundled one that we can try. -qt-xkb or something in the configure args

illwieckz · 2025-11-14T11:53:04Z

The backports list file was removed:

E: Release 'bullseye-backports' for 'cmake' was not found

Also I noticed the backport url could use http, making it possible to be fetched before installing ca-certificates. Debian does it own crypto thing and doesn't need to trust the carrier as it can validate the package whatever the way it was sourced. This makes possible to do a single apt update.

That ca-certificates package is likely needed for the curl download, but then keeping it implicit from curl now sounds fine.

That's doable:

RUN echo 'deb http://archive.debian.org/debian bullseye-backports main' > /etc/apt/sources.list.d/backports.list \
    && apt-get update \
    && apt-get install -y \
    autoconf \
    autopoint \
    curl \
    gettext \
    git \
    g++ \
    libgl1-mesa-dev \
    libtool \
    libx11-xcb-dev \
    libxcb-glx0-dev \
    libxkbcommon-x11-dev \
    make \
    ninja-build \
    perl \
    p7zip-full \
    pkg-config \
    python \
    xz-utils \
    zlib1g-dev \
    $XCB_MINIMUM_PACKAGES \
    && apt-get install -y \
    cmake/bullseye-backports \
    && apt-get clean

illwieckz · 2025-11-16T23:19:35Z

The commit spam no-pie/no-pic mistakenly deletes this line from the OpenSSL build:

RUN ./config --prefix=/openssl --openssldir=/dev/null no-shared no-apps no-autoload-config no-capieng no-dso no-dynamic-engine no-engine no-loadereng no-module -Os

illwieckz · 2025-11-17T00:18:19Z

Dockerfile

+# Note: {foo:+bar} here is a syntax of the Dockerfile, not the shell!
+ENV IPO_ARG=${release:+-DCMAKE_INTERPROCEDURAL_OPTIMIZATION=ON}
+RUN echo IPO_ARG ${IPO_ARG}
+RUN BUILDQT_CMAKE_ARGS="${IPO_ARG} -DCMAKE_POSITION_INDEPENDENT_CODE=OFF -DFEATURE_reduce_relocations=OFF" CXXFLAGS='-fno-pic -no-pie' CFLAGS='-fno-pic -no-pie' PKG_CONFIG_PATH=/openssl/lib64/pkgconfig ./build-qt.sh && mv qt /qt && rm -rf /build-qt


-DCMAKE_POSITION_INDEPENDENT_CODE=OFF ${IPO_ARG} instead of ${IPO_ARG} -DCMAKE_POSITION_INDEPENDENT_CODE=OFF

What's the difference?

${IPO_ARG} -DCMAKE_POSITION_INDEPENDENT_CODE=OFF always disable IPO.

slipher · 2025-11-17T02:03:58Z

The commit spam no-pie/no-pic mistakenly deletes this line from the OpenSSL build:
RUN ./config --prefix=/openssl --openssldir=/dev/null no-shared no-apps no-autoload-config no-capieng no-dso no-dynamic-engine no-engine no-loadereng no-module -Os

Fixed

slipher · 2025-11-18T13:03:54Z

There is now a Windows build, which seems to work in non-release mode. (But if you pass release=1, you get an internal compiler error.)

slipher · 2025-11-20T05:03:16Z

Fixed issue with the app not exiting when all windows are closed.

Also added the toolchain file for MinGW which I forgot to add before.

illwieckz · 2025-11-20T05:19:23Z

Fixed issue with the app not exiting when all windows are closed.

Thanks a lot!

slipher · 2025-11-28T03:57:55Z

Finally got the modal dialog thing. Turns out it is not implemented for "non-native" dialogs until Qt 6.10. The Debian distro libraries used "native" dialogs so that's why the problem could not be reproduced there. I tried building with version 6.10 but then the dialog wouldn't open at all. So I backported the commit to 6.8.

Something that is broken is the render of the “Continue reading” link, the HTML code explicitly says this should be cyan and aligned to the right, while it is rendered as white and aligned to the left. Actually that look isn't that bad, and we may decide to do it purposely, but that's not what the code is asking for.

Fixed

illwieckz · 2025-11-28T06:21:37Z

You may be interested in my build-qt: per-module patch application patch to simplifies the application of patches, this is something I wrote when I added a patch for qtshadertools but I rebased it and rewrote it to be even more generic so it could handle without custom code the qtdeclarative patch you added.

illwieckz · 2025-11-28T06:23:28Z

I see no difference with “Continue reading”.

slipher · 2025-11-28T13:20:40Z

Maybe it would be better to just test slipher/qt6-combined since I keep forgetting to update the slipher/qt6 pointer.

slipher · 2025-11-28T13:22:19Z

Maybe it would be better to just test slipher/qt6-combined since I keep forgetting to update the slipher/qt6 pointer.

Never mind, I don't think it was in there either. Pushed both

illwieckz · 2025-11-28T22:42:34Z

This is starting to look (the PR) very good!

Save the checksums of Qt and OpenSSL archives in the repo instead of downloading them at the same time as the code.

This prevents warning spam from Qt 6's rcc tool.

illwieckz · 2025-12-03T04:02:09Z

About fontconfig support, I noticed we require it on Linux to be able to render the names of the user's folders in the install directory picker window.

We not only have to render our blog posts, we also have to render any character in a file path on user's computers.

illwieckz · 2025-12-03T09:02:47Z

Another regression spotted: when we hover the “Continue reading” link, the mouse pointer doesn't turn into a finger pointing hand.

slipher · 2025-12-16T00:57:48Z

Another regression spotted: when we hover the “Continue reading” link, the mouse pointer doesn't turn into a finger pointing hand.

It works for me. I don't see any difference

slipher · 2025-12-18T20:03:07Z

It turns out LTO can't be used with mingw because Qt adds the incompatible -Wa,-mbig-obj flag.

illwieckz · 2025-12-19T16:08:26Z

The “ripple animation” stuff looks pretty optional to me, so I guess what's remaining is the macOS stuff.

slipher · 2025-12-31T15:23:29Z

This is about ready, except I couldn't fix CodeQL because Ubuntu offers a very old Qt6 and there are no other distros for Github Action.

As for further size optimizations I removed Fluid's SVGs that we don't use since it is the biggest and easiest win. Other ones that are more complex like stripping shader files can go in another PR.

Update from Qt 5.14 with qmake build system to Qt 6.8 with CMake build system. Fluid and Quazip dependencies are also updated to get versions compatible with these changes. - Migrate from qmake build system to CMake. A toolchain file is now needed for MinGW, which was taken from Daemon. - Update Quazip. Nothing special required here other than switching to CMake. - Update Fluid. Fluid's CMake build system does some things that are incompatible with the updater, such as building its code as a shared library, so I had to add a CMake file of our own with a modified version. Besides the build system change, some QML APIs needed to be migrated. - Do Qt 5->6 API migrations - Remove version numbers from QML imports. Versioned imports of the standard QML libraries seem to be discouraged now as the documentation no longer indicates their versions. - Add build-qt.sh which is used to build Qt for all platforms and applies various patches that we ended up needing. Switch from building with the single archive to separate submodules since the single archive is so big that just extracting it takes a long time. - Make various efforts to reduce binary size, since the initial Qt6 iteration had a huge size increase: - Disable as many features as possible when building Qt - Use LTO on Linux. For Windows it was impossible due to an incompatible flag -Wa,-mbig-obj - Enable some other size-reducing flags for the Qt build - Patch rcc to use compression by default - Ensure there are no unacceptable dynamic dependencies on Linux: - Use static libxcb-* in the Docker build - Patch some Qt stuff to avoid libxkbcommon-x11 dependency - Always select Ninja as the CMake generator in build scripts. This is recommended by Qt - Bump Debian image for mingw build from Bullseye to Trixie since the gcc was too old and there is no reason not to use the latest toolchain on Windows. - Make some efforts to update the CodeQL build script. However, the Github Actions-provided Ubuntu's Qt is too old (6.4) so the workflow must be disabled for now. Co-Authored-By: Thomas Debesse <[email protected]>

The API became available in Qt 5.15.

Saves 0.7M on binary size.

slipher · 2026-01-04T15:02:48Z

Ready for review. For CodeQL the plan is to disable it until an Ubuntu image with at least Qt 6.8 comes out.

illwieckz · 2026-01-04T20:57:51Z

I deeply proofread it on many iterations. Assuming you have tested Windows and macOS building and running, that now looks ready to me as well.

illwieckz

LGTM.

illwieckz reviewed Nov 12, 2025

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illwieckz reviewed Nov 12, 2025

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slipher force-pushed the slipher/qt6 branch from c812e31 to 0ec3df1 Compare November 13, 2025 02:58

illwieckz mentioned this pull request Nov 14, 2025

Things to do to reduce the executable binary size #164

Open

6 tasks

slipher force-pushed the slipher/qt6 branch 3 times, most recently from aa400d7 to 780eba1 Compare November 16, 2025 13:36

illwieckz reviewed Nov 17, 2025

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slipher force-pushed the slipher/qt6 branch from 780eba1 to ab9f023 Compare November 17, 2025 02:03

slipher force-pushed the slipher/qt6 branch from 787e06b to 1c42103 Compare November 20, 2025 05:01

slipher force-pushed the slipher/qt6 branch from 1c42103 to f5094a0 Compare November 21, 2025 13:26

slipher force-pushed the slipher/qt6 branch from c7cbcea to 4e4079a Compare November 28, 2025 03:38

slipher added 2 commits November 30, 2025 11:26

Docker: hard-code checksums of downloaded deps

2100044

Save the checksums of Qt and OpenSSL archives in the repo instead of downloading them at the same time as the code.

Docker: set LANG=C.UTF-8

fe70d85

This prevents warning spam from Qt 6's rcc tool.

slipher force-pushed the slipher/qt6 branch from 0a8f417 to 9ac2a49 Compare December 18, 2025 20:00

slipher force-pushed the slipher/qt6 branch from ab6994a to 5b47610 Compare December 31, 2025 13:09

slipher force-pushed the slipher/qt6 branch 2 times, most recently from 5bc0080 to 0d001d6 Compare January 4, 2026 14:53

slipher and others added 3 commits January 4, 2026 08:59

Use QProcess::splitCommand instead of own function

adf7074

The API became available in Qt 5.15.

Embed only used icons from Fluid

1645a84

Saves 0.7M on binary size.

slipher force-pushed the slipher/qt6 branch from 0d001d6 to 1645a84 Compare January 4, 2026 15:01

slipher marked this pull request as ready for review January 4, 2026 15:02

illwieckz approved these changes Jan 4, 2026

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slipher merged commit 06ce270 into master Jan 6, 2026
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slipher deleted the slipher/qt6 branch January 6, 2026 01:13

slipher mentioned this pull request Jan 6, 2026

Re-enable CodeQL when possible #172

Open

Qt6 + CMake migration #165

Qt6 + CMake migration #165

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