Drop Support for Qt <5.15.2

[Nerixyz]

Reasoning

The main reason to keep support for Qt 5.12.12, in my understanding, is/was to have an easy path for users of Ubuntu 20.04 using the .deb artifact.

Now, all up-to-date distributions of Linux mentioned in BUILDING_ON_LINUX.md provide Qt ^5.15.2. Users of Windows and macOS can update Qt using the official Qt installer (or additionally brew in the case of macOS).

Supporting Qt 5.12.12 is slowing down development while providing little to no value. This mainly shows in the widely QStrings which got their specialization for std::hash in 5.14, thus QStringHash has to be included everywhere a std-container like std::unordered_map or std::unordered_set with a QString as a key is used. Furthermore, some important QStringView methods were added in 5.15.2, which is needed for Qt6 compatibility, as QStringRef was removed.

I think it's worth considering dropping support for these older Qt versions.

OS Support

Windows

Qt Installer only shows the latest version (5.15.2).

Mac

Qt Installer only shows the latest version.

Through brew: 5.15.8

The build instructions should be updated to mention that 5.15.2 is required.

Linux

Ubuntu

Package	Focal (20.04) EOS Apr-2025	Jammy (22.04) EOS Apr-2027
qttools-opensource-src ⇾ qttools5-dev	5.12.8-0ubuntu1	5.15.3-1
qtmultimedia-opensource-src ⇾ qtmultimedia5-dev	5.12.8-0ubuntu1	5.15.3-1
qtimageformats-opensource-src ⇾ qt5-image-formats-plugins	5.12.8-0ubuntu1	5.15.3-1
qtsvg-opensource-src ⇾ libqt5svg5-dev	5.12.8-0ubuntu1	5.15.3-1

However, you can install Qt 5.15.2 on Focal and earlier using either the Qt online installer or PPAs. It was mentioned, that the last LTS is supported.

The build instructions should be updated to mention Jammy (22.04) as the minimum (suggested) version.

Arch Linux

Uses Qt 5.15.2.

Fedora

Fedora 35 (Nov-21) provides 5.15.2 - 36 (May-22) and 37 (Nov-22) provide 5.15.3 [unsure about older versions].

The build instructions should be updated to mention 35 as the minimum (known) version.

NixOS

NixOS provides in Qt 5.12.3 in 22.05+ [unsure about older versions].

The build instructions should be updated to mention 22.05 as the minimum (known) version.

[pajlada]

Requirements

• Split up Ubuntu CI to build on 20.04 & 22.04 (and provide 20.04-specific and 22.04-specific deb builds)

[Nerixyz]

With Qt 6.5 scheduled to release on the 3rd of April. I think the CI can be updated to add experimental builds with Qt 6 (this discussion seems to be a decent place to discuss this).

Since Ubuntu 20.04 requires 5.12, this version can't be dropped there. However, it can be dropped on Windows and macOS. I propose the following builds in CI:

Qt Version	FreeBSD	macOS	Ubuntu	Windows
5.12.12	❌	❌	✅	❌
5.15.2	✅	✅	✅	✅
6.2.4	?	?	✅	?
6.5.0	?	✅	❌	✅

It would be fine for now to only build on 6.2.4 and ignore the latest version. 6.2.4 is needed because that's what Ubuntu 22.04 uses. You can read what's new in each version here. The CI build artifacts would be marked "experimental".

Status on known Qt 6 bugs in Chatterino

There are no more major bugs with Qt 6.

[LosFarmosCTL]

Status on known Qt 6 bugs in Chatterino

Adding to this, Qt 6 would enable us to build M1 versions for macOS.

This fixes #4445 and #2300

[pajlada]

I don't think M1 versions are that simple, we still require CI to support it & building with Qt 5.15 on M1 already seems to work

[pajlada]

To respond to Nerixyz's comment: This version grid looks good to me

[LosFarmosCTL]

I don't think M1 versions are that simple, we still require CI to support it & building with Qt 5.15 on M1 already seems to work

There would have to be changes to the CI yeah, but it doesn't require GitHub to support Apple Silicon or anything.

While 5.15 can compile an Apple Silicon binary, the big advantage of Qt 6 (and commercial 5.15.19) is that it supports universal binaries, meaning there can just be one version thats compiled on Intel and works for both platforms.

[iProdigy]

Another reason to work towards Qt 6.5.0: OpenSSL 1.1.1 is EOL on 2023-09-11 (& only 6.5+ are built against OpenSSL 3)

[Nerixyz]

As a test, I removed Qt 5.12 support in Nerixyz@0e2fdff. This removes the deb artifact on Ubuntu 20.04. The AppImage as well as the Flatpak however both contain Qt 5.15 (this would [probably] make it possible to move to Qt 6 as well).

Additionally, I updated GCC to version 10 for better C++ 20 compatibility.

---

Since opening this discussion, OBS also announced dropping support for Ubuntu 20.04 (and Qt 5) in obsproject/obs-studio#9055.

[Nerixyz]

🎉 It's done, yay!

_{Sidenote because I can't find a good place: std::map and std::unordered_map support heterogeneous lookup, maybe we could use that in some cases (e.g. LinkParser could profit).}