Non deterministic build for kirigami

[Santiago Vila]

Hello.

When I try to build (the Debian package of) kirigami, which is called
kf6-kirigami here, I get different results depending on the number of
CPUs of the building machine.

On systems with 2 CPUs, the build always succeeds.

On systems with 1 CPU, the build always fails with an error like this:

dpkg-gensymbols: error: some symbols or patterns disappeared in the symbols file: see diff output below
dpkg-gensymbols: warning: debian/libkirigamidelegates6/DEBIAN/symbols does not match completely debian/libkirigamidelegates6.symbols
--- debian/libkirigamidelegates6.symbols (libkirigamidelegates6_6.23.1-1_amd64)
+++ dpkg-gensymbolscDH3iN       2026-04-18 04:35:57.198683390 +0000
@@ -1,12 +1,12 @@
 libKirigamiDelegates.so.6 libkirigamidelegates6 #MINVER#
 * Build-Depends-Package: libkirigami-dev
  _Z45qml_register_types_org_kde_kirigami_delegatesv at Base 6.0.0
- _ZGVZN9QMetaType21registerConverterImplI5QListIP7QObjectE9QIterableI13QMetaSequenceEEEbSt8functionIFbPKvPvEES_S_E10unregister at Base 6.23.0
- _ZGVZN9QMetaType23registerMutableViewImplI5QListIP7QObjectE9QIterableI13QMetaSequenceEEEbSt8functionIFbPvS9_EES_S_E10unregister at Base 6.23.0
- _ZN13QMetaSequence12MetaSequenceI5QListIP7QObjectEE5valueE at Base 6.23.0
- _ZTIZN9QMetaType17registerConverterI5QListIP7QObjectE9QIterableI13QMetaSequenceEN9QtPrivate33QSequentialIterableConvertFunctorIS4_EEEEbT1_EUlPKvPvE_ at Base 6.23.0
- _ZTIZN9QMetaType19registerMutableViewI5QListIP7QObjectE9QIterableI13QMetaSequenceEN9QtPrivate37QSequentialIterableMutableViewFunctorIS4_EEEEbT1_EUlPvSC_E_ at Base 6.23.0
- _ZTSZN9QMetaType17registerConverterI5QListIP7QObjectE9QIterableI13QMetaSequenceEN9QtPrivate33QSequentialIterableConvertFunctorIS4_EEEEbT1_EUlPKvPvE_ at Base 6.23.0
- _ZTSZN9QMetaType19registerMutableViewI5QListIP7QObjectE9QIterableI13QMetaSequenceEN9QtPrivate37QSequentialIterableMutableViewFunctorIS4_EEEEbT1_EUlPvSC_E_ at Base 6.23.0
- (optional=templinst)_ZZN9QMetaType21registerConverterImplI5QListIP7QObjectE9QIterableI13QMetaSequenceEEEbSt8functionIFbPKvPvEES_S_E10unregister at Base 6.23.0
- (optional=templinst)_ZZN9QMetaType23registerMutableViewImplI5QListIP7QObjectE9QIterableI13QMetaSequenceEEEbSt8functionIFbPvS9_EES_S_E10unregister at Base 6.23.0
+#MISSING: 6.23.1-1# _ZGVZN9QMetaType21registerConverterImplI5QListIP7QObjectE9QIterableI13QMetaSequenceEEEbSt8functionIFbPKvPvEES_S_E10unregister at Base 6.23.0
+#MISSING: 6.23.1-1# _ZGVZN9QMetaType23registerMutableViewImplI5QListIP7QObjectE9QIterableI13QMetaSequenceEEEbSt8functionIFbPvS9_EES_S_E10unregister at Base 6.23.0
+#MISSING: 6.23.1-1# _ZN13QMetaSequence12MetaSequenceI5QListIP7QObjectEE5valueE at Base 6.23.0
+#MISSING: 6.23.1-1# _ZTIZN9QMetaType17registerConverterI5QListIP7QObjectE9QIterableI13QMetaSequenceEN9QtPrivate33QSequentialIterableConvertFunctorIS4_EEEEbT1_EUlPKvPvE_ at Base 6.23.0
+#MISSING: 6.23.1-1# _ZTIZN9QMetaType19registerMutableViewI5QListIP7QObjectE9QIterableI13QMetaSequenceEN9QtPrivate37QSequentialIterableMutableViewFunctorIS4_EEEEbT1_EUlPvSC_
[...]

This admittedly looks like a packaging error in the Debian package,
but it does not make any sense at all, because the debian/rules script
is absolutely minimal.

My theory is that there is a bug in one of the CMakeLists.txt files.

In case it helps, I could provide a VM where this happens all the
time, but I guess configuring GRUB with GRUB_CMDLINE_LINUX="nr_cpus=1"
would also work.

Naturally, a bug which only happens on a Debian system has no place
here, but I suppose it would be possible to check (in a OS-agnostic
way) that the outcome of the build is different by using a command
like this:

nm --dynamic --defined-only libKirigamiDelegates.so.6 | grep QMetaSequence

For reference, I've put two build logs, one failed and the other successful
here:

https://people.debian.org/~sanvila/build-logs/kf6-kirigami/

Thanks.