Keeping Qt5 alive on Gentoo (the stuff 5.15 LTS mirror)¶

::gentoo last-rited the entire dev-qt slot 5 set on 2026-05-15 (bug #948836) — "last rites" is Gentoo's formal removal announcement, and a slot is Gentoo's mechanism for keeping incompatible major versions installed side by side (for example, Qt5 = :5 and Qt6 = :6) — and no longer carries the slot-5 split set. Plenty of software hasn't finished its Qt6 port, including large scientific GUIs such as sci-physics/mantid, PyQt5 apps, and qscintilla-based editors.

stuff carries the Qt5 split-module set at 5.15.19-lts-lgpl, excluding QtWebEngine, with the KDE Qt5 Patch Collection applied, so those apps keep building. It's a deliberate bridge, not a destination — it exists until its consumers move to Qt6.

Quickstart¶

Quickstart

With the overlay enabled and its keywords accepted (Setup), emerge a Qt5 consumer; it resolves against the overlay's 5.15.19. The overlay's profile re-allows the masked dev-qt:5 set, so no manual unmask is needed. As root:

root #

emerge -av sci-physics/mantid        # example Qt5 consumer

What the overlay carries¶

The dev-qt slot 5 split-module set at 5.15.19-lts-lgpl, except QtWebEngine — Qt Group's LTS release (2025-11-25, which ::gentoo never picked up), with the KDE Qt5 Patch Collection applied on top. That's newer than ::gentoo's final 5.15.18.
dev-python/pyqt5 (5.15.11) + dev-python/pyqt5-sip — PyQt5 revived after ::gentoo's treeclean.
x11-libs/qscintilla-2.14.1-r1 — the last Qt5-compatible qscintilla. The Qt6-only -r2 is masked in the overlay so portage keeps -r1.

How to use it¶

Enable the overlay. Its profiles/package.unmask re-allows the dev-qt/*:5 set that ::gentoo masked — applied automatically for anyone with the overlay enabled, so nothing is unmasked by hand.
Accept ~arch keywords. The Qt5 ebuilds are keyworded testing (~amd64 …). On stable amd64, accept them. The simplest form takes the whole overlay:
/etc/portage/package.accept_keywords/stuff
```
*/*::stuff ~amd64
```
or scope it to just the Qt5 pieces:
/etc/portage/package.accept_keywords/stuff
```
dev-qt/*::stuff       ~amd64
dev-python/pyqt5      ~amd64
dev-python/pyqt5-sip  ~amd64
x11-libs/qscintilla   ~amd64
```
Emerge the Qt5 consumer. It resolves its dev-qt/*:5 dependencies against the overlay's 5.15.19. The set can also be pulled directly (emerge -av dev-qt/qtcore:5 dev-qt/qtwidgets:5 …).

Under the hood¶

Each module is built by the overlay's qt5-build.eclass. The KDE Qt5 Patch Collection is cut per-module and mirrored to extra-stuff as version-pinned distfiles; the eclass fans the SRC_URI across the GitHub / Codeberg / GitLab raw mirrors, while the upstream Qt tarballs come from download.qt.io.
profiles/package.unmask re-allows the slot; profiles/package.mask pins qscintilla to the Qt5 -r1.

When can the mirror be dropped?¶

The mirror is a bridge: it exists only until its consumers finish their Qt6 ports. To see what still pulls Qt5, list the reverse dependencies of the base module with app-portage/gentoolkit, as a normal user:

user $

equery depends dev-qt/qtcore:5

Once nothing but the dev-qt/*:5 set itself depends on Qt5, the consumers have moved on and the overlay's Qt5 can be retired — emerge --deselect the apps, then emerge --depclean.

Caveats¶

It's a temporary bridge

This mirror exists so Qt5 consumers keep working through their Qt6 ports — it will be dropped once those land. Don't start new work against Qt5.

qtwebengine:5 is not carried (it's masked) — apps that need the Qt5 WebEngine won't find it here.
Tree status. ::gentoo's Qt5 removal has executed. The overlay is now the source for this split set, and a Qt5 consumer that isn't using it will fail to resolve.
How long the mirror lives. Best-effort, no hard end-of-life date: it is maintained while its consumers still need it and retired (archived in git history, not erased) once they have moved to Qt6 — the reverse-dependency check above is the exit criterion.

Troubleshooting¶

Cannot mix incompatible Qt library (version 0x05XXXX) — after a Qt5 point bump, a style or platform-theme plugin built against the previous Qt5 refuses to load (these use Qt private headers and pin an exact version, not just a matching soname). Rebuild the consumers with emerge @preserved-rebuild (@preserved-rebuild is a built-in portage set, like @world, that rebuilds packages still linked against old library copies); Gentoo's subslot dependencies rebuild most Qt5 consumers automatically on the bump, and this catches anything left with preserved libraries.

Theming Qt5 apps outside KDE

Qt5 follows the desktop's theme under KDE / GNOME but falls back to Fusion elsewhere. Install the qt5ct package and set QT_QPA_PLATFORMTHEME=qt5ct (or force a widget style with QT_STYLE_OVERRIDE) to control icons, fonts, and style.

Running Qt5 apps on Wayland

The overlay carries dev-qt/qtwayland:5, so a Qt5 app can use the Wayland backend directly with QT_QPA_PLATFORM=wayland; otherwise it runs through XWayland via the xcb plugin.