Provide coinstallability for Qt 5 and Qt 6 themes #1789

Vogtinator · 2023-09-09T20:02:53Z

sddm-greeter is already a separate process, so it's actually rather simple to support themes using Qt 5 and themes using Qt 6 on the same system. This PR achieves this by installing the greeter specific files with a -qt6 suffix when BUILD_FOR_QT6=ON and dynamically choosing which greeter to execute based on the QtVersion= property in the theme metadata.desktop. For backwards compatibility, this defaults to 5 if not present.

This means that all current Qt 6 themes (i.e. just breeze?) will have to add QtVersion=6, otherwise the Qt 5 greeter will be used.

Open topics:

Are translations in .qm format compatible across Qt major versions? I couldn't find any info for this. If they are compatible, then the -qt suffix for the translation dir can be avoided. Themes can also provide .qm files.
Should the QtVersion property allow to specify multiple versions as fallback? I'm not sure whether it's practical to have a theme which supports multiple major versions, especially if .qm files are not necessarily compatible.
What should the example themes specify as Qt version? elarun currently has a broken background with Qt 6.
For after the merge: Document the QtVersion property and behaviour

With #1790 on top, the Qt 6 build will automatically build and install the Qt 5 greeter as well.

This is needed for sddm/sddm#1789 to have SDDM run a Qt 6 greeter.

Conan-Kudo · 2023-09-15T13:34:39Z

src/greeter/CMakeLists.txt

+    # Keep the unversioned name for Qt5. When upgrading SDDM, the old daemon
+    # might still be running and only know about "sddm-greeter". Keeping the
+    # previous name around also helps users calling it directly.
+    set(GREETER_TARGET sddm-greeter)


Why not just handle the unversioned name via symlink for this purpose? I'd rather us just change to versioned names unless we intend to quickly drop Qt5 support.

What's the benefit of using a symlink instead?

I decided against it because it's one more file and installing a symlink with cmake needs a custom command...

It does? file(CREATE_LINK) has been available since CMake 3.14...

Would need to check whether bumping the requirement would be ok.

set(CMAKE_CXX_STANDARD 17) was added in CMake 3.20, so you already require that as a minimum.

That was most likely an oversight, but nobody complained so it's probably ok 🤷

set(CMAKE_CXX_STANDARD 17) was added in CMake 3.20, so you already require that as a minimum.

That was actually in CMake 3.8: https://cmake.org/cmake/help/latest/prop_tgt/CXX_STANDARD.html#prop_tgt:CXX_STANDARD

Oh welp, right, C++20 was in CMake 3.20. My bad.

evelikov · 2023-10-12T10:10:19Z

Does the daemon need a similar -qt6 handling or is it expected that mixing qt5 daemon and qt6 greeter (or vice-versa) will still work?

Vogtinator · 2023-10-12T10:39:30Z

Does the daemon need a similar -qt6 handling or is it expected that mixing qt5 daemon and qt6 greeter (or vice-versa) will still work?

Both combinations are valid. #1790 makes that even more explicit.

Vogtinator · 2023-11-13T18:14:52Z

@aleixpol @davidedmundson Could you provide input on the open topics?

This is needed for sddm/sddm#1789 to have SDDM run a Qt 6 greeter.

Vogtinator · 2023-11-27T07:39:46Z

@aleixpol @davidedmundson Could you provide input on the open topics?

Ping! This needs to be done before anyone develops themes without QtVersion=6 which will then inadvertedly break after this is merged.

davidedmundson · 2023-11-27T14:06:06Z

Are translations in .qm format compatible across Qt major versions? I couldn't find any info for this. If they are compatible, then the -qt suffix for the translation dir can be avoided. Themes can also provide .qm files.

Diff implies that pragmatically they are.
The DTD looks the same https://doc.qt.io/qt-6/linguist-ts-file-format.html and that can't change on a whim.

Should the QtVersion property allow to specify multiple versions as fallback? I'm not sure whether it's practical to have a theme which supports multiple major versions, especially if .qm files are not necessarily compatible.

I would say no, the point of this is to have SDDM do the work so theme devs don't have to. QML is not ifdef-able and trying to support multiple versions has not been easy for other places.

What should the example themes specify as Qt version? elarun currently has a broken background with Qt 6.

The default theme (elarun) has to work in both. That gets baked in via qrc into both executables.
On hitting a QML error we fallback to the default theme in process without restarting the greeter.

We also have the case at a cmake level of not building a Qt6 greeter at which point we want these to work. I would suggest leave them alone as-is for now then bump when we make Qt6 mandatory.

I could not reproduce the Image issue.

For after the merge: Document the QtVersion property and behaviour

Definitely, especially the part for packagers

Vogtinator · 2023-11-27T14:24:47Z

Are translations in .qm format compatible across Qt major versions? I couldn't find any info for this. If they are compatible, then the -qt suffix for the translation dir can be avoided. Themes can also provide .qm files.

Diff implies that pragmatically they are. The DTD looks the same https://doc.qt.io/qt-6/linguist-ts-file-format.html and that can't change on a whim.

That's for TS files. QM files are basically serialized Qt hashes and I have no idea whether that's meant to be stable... Arguably if they're compatible now, then using the Qt 5 files for Qt 6 is fine, but not necessarily the other way around.

Should the QtVersion property allow to specify multiple versions as fallback? I'm not sure whether it's practical to have a theme which supports multiple major versions, especially if .qm files are not necessarily compatible.

I would say no, the point of this is to have SDDM do the work so theme devs don't have to. QML is not ifdef-able and trying to support multiple versions has not been easy for other places.

Yep...

What should the example themes specify as Qt version? elarun currently has a broken background with Qt 6.

The default theme (elarun) has to work in both. That gets baked in via qrc into both executables. On error we fallback to the default theme on QML error in process without restarting the greeter.

We also have the case at a cmake level of not building a Qt6 greeter at which point we want these to work. I would suggest leave them alone as-is for now then bump when we make Qt6 mandatory.

I could not reproduce the Image issue.

Ok.

For after the merge: Document the QtVersion property and behaviour

Definitely, especially the part for packagers

Can do. Currently the wiki is the best documentation source or should I put that into README?

Vogtinator · 2023-12-07T09:28:40Z

Ping

Vogtinator · 2024-01-20T17:08:40Z

Ping.

evelikov · 2024-01-22T16:30:12Z

I patched the sddm package on my Arch box and installed it. Works like a charm and the code is simple enough.

Feel free to consider this "Tested-by" and "Reviewed-by" fwiw o/

evelikov · 2024-01-29T16:34:54Z

src/common/ThemeMetadata.cpp

    void ThemeMetadata::setTo(const QString &path) {
        QSettings settings(path, QSettings::IniFormat);
        // read values
        d->mainScript = settings.value(QStringLiteral("SddmGreeterTheme/MainScript"), QStringLiteral("Main.qml")).toString();
        d->configFile = settings.value(QStringLiteral("SddmGreeterTheme/ConfigFile"), QStringLiteral("theme.conf")).toString();
        d->translationsDirectory = settings.value(QStringLiteral("SddmGreeterTheme/TranslationsDirectory"), QStringLiteral(".")).toString();
+        d->qtVersion = settings.value(QStringLiteral("SddmGreeterTheme/QtVersion"), 5).toInt();


Shouldn't we set QtVersion for the themes we ship? Casual grep suggests that these would need an update:

data/themes/elarun/metadata.desktop data/themes/maldives/metadata.desktop data/themes/maya/metadata.desktop src/greeter/theme/metadata.desktop

While I haven't tried the Qt6 side, just yet. I've build this with Qt5 and it works like a charm.

With the above .desktop/QtVersion handled, I think we're good to merge.

Shouldn't we set QtVersion for the themes we ship? Casual grep suggests that these would need an update:

Kind of. The builtin themes are only semi-compatible with Qt 6 :-/

That's also mentioned in the PR message:

What should the example themes specify as Qt version? elarun currently has a broken background with Qt 6.

When not building for Qt 5, give the sddm-greeter binary a Qt version suffix. Also version the translation directory.

metadata.desktop in the theme directory has a new key "QtVersion" which defaults to 5. If it's not 5, sddm-greeter-qt${QtVersion} will be used to show the theme.

This is needed for sddm/sddm#1789 to have SDDM run a Qt 6 greeter.

Vogtinator added the qt6 Qt 6 porting label Sep 9, 2023

Vogtinator mentioned this pull request Sep 9, 2023

Allow building sddm-greeter for both Qt 5 and Qt 6 in one go #1790

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kdesysadmin pushed a commit to KDE/plasma-workspace that referenced this pull request Sep 14, 2023

lookandfeel/sddm-theme/metadata.desktop: Add QtVersion=6

571a1dd

This is needed for sddm/sddm#1789 to have SDDM run a Qt 6 greeter.

Vogtinator force-pushed the qtcoinst branch from 4bdcd47 to 6766038 Compare September 14, 2023 18:41

Conan-Kudo suggested changes Sep 15, 2023

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Vogtinator mentioned this pull request Sep 22, 2023

nixos/sddm: enable Wayland support NixOS/nixpkgs#242009

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kdesysadmin pushed a commit to KDE/plasma-workspace that referenced this pull request Nov 27, 2023

lookandfeel/sddm-theme/metadata.desktop: Add QtVersion=6

1589df2

This is needed for sddm/sddm#1789 to have SDDM run a Qt 6 greeter.

Vogtinator force-pushed the qtcoinst branch from 6766038 to 3df79d4 Compare December 1, 2023 10:07

davidedmundson approved these changes Jan 22, 2024

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Vogtinator force-pushed the qtcoinst branch from 3df79d4 to 5de0967 Compare January 28, 2024 16:17

evelikov reviewed Jan 29, 2024

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Vogtinator force-pushed the qtcoinst branch from 5de0967 to 4cc08ef Compare February 20, 2024 10:31

Vogtinator added 2 commits February 20, 2024 11:33

Make sddm-greeter for Qt 5 and Qt 6 coinstallable

f6794b1

When not building for Qt 5, give the sddm-greeter binary a Qt version suffix. Also version the translation directory.

Let themes specify the used version of Qt

348da41

metadata.desktop in the theme directory has a new key "QtVersion" which defaults to 5. If it's not 5, sddm-greeter-qt${QtVersion} will be used to show the theme.

Vogtinator force-pushed the qtcoinst branch from 4cc08ef to 348da41 Compare February 20, 2024 10:33

Vogtinator merged commit 115f01b into sddm:develop Feb 20, 2024
12 of 13 checks passed

Vogtinator deleted the qtcoinst branch February 20, 2024 10:35

kdesysadmin pushed a commit to KDE/plasma-desktop that referenced this pull request Apr 3, 2024

lookandfeel/sddm-theme/metadata.desktop: Add QtVersion=6

3f38fec

This is needed for sddm/sddm#1789 to have SDDM run a Qt 6 greeter.

kdesysadmin pushed a commit to KDE/plasma-desktop that referenced this pull request Apr 5, 2024

lookandfeel/sddm-theme/metadata.desktop: Add QtVersion=6

92d1df7

This is needed for sddm/sddm#1789 to have SDDM run a Qt 6 greeter.

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Provide coinstallability for Qt 5 and Qt 6 themes #1789

Provide coinstallability for Qt 5 and Qt 6 themes #1789

Vogtinator commented Sep 9, 2023 •

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Provide coinstallability for Qt 5 and Qt 6 themes #1789

Provide coinstallability for Qt 5 and Qt 6 themes #1789

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