https://bugs.kde.org/show_bug.cgi?id=525989
Bug ID: 525989
Summary: Application order for a MIME type is not deterministic
when offers tie on preference
Classification: Frameworks and Libraries
Product: frameworks-kservice
Version First 6.26.0
Reported In:
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: ---
The order KApplicationTrader returns for a MIME type, and therefore the default
application, changes between runs of kbuildsycoca6 on an unchanged system.
Installing any package rebuilds ksycoca, so a user's default application for a
type can silently change after an unrelated package install.
STEPS TO REPRODUCE
1. Install two desktop files claiming the same type, with no mimeapps.list
entry for it:
/usr/share/applications/tiebreak-alpha.desktop
[Desktop Entry]
Type=Application
Name=Tiebreak alpha
Exec=/bin/true %u
MimeType=x-scheme-handler/tiebreaktest;
/usr/share/applications/tiebreak-beta.desktop (same, Name=Tiebreak beta)
2. kbuildsycoca6 --noincremental
3. KApplicationTrader::preferredService("x-scheme-handler/tiebreaktest")
4. Repeat from 2.
OBSERVED RESULT
The winner alternates. 12 runs: 8 tiebreak-alpha, 4 tiebreak-beta. With
QT_HASH_SEED=0 it is stable across runs.
Same thing with real applications where calibre and libreoffice both claim
application/vnd.openxmlformats-officedocument.wordprocessingml.document. 20
runs: 9 libreoffice-writer, 6 calibre-gui, 3 calibre-ebook-edit, 2
calibre-ebook-viewer.
EXPECTED RESULT
Same input, same order.
CAUSE
KBuildServiceFactory::populateServiceTypes() iterates m_entryDict
(KSycocaEntryDict is a QHash) and appends one offer per service, all with
preference 1. KServiceOffer::operator< compares only mimeTypeInheritanceLevel
and then preference. saveOfferList() sorts with std::stable_sort, so offers
that tie on both keep their insertion order, which is QHash iteration order,
randomized per process by Qt.
Any type whose top candidates are not separated by a mimeapps.list entry is
decided by the hash seed.
SUGGESTED FIX
Add a deterministic last-resort key to KServiceOffer::operator<, for instance
KService::storageId(), the way 7e643dbc did it for KServiceGroup.
Checked master: operator<, the stable_sort and the m_entryDict iteration are
unchanged. 9e9f4de6 fixed a related order dependence in
KOfferHash::addServiceOffer, but not this one.
SOFTWARE/OS VERSIONS
kservice 6.28.0 and 6.26.0, Plasma 6.6.5, Qt 6, ALT Linux x86_64.
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