XPost: linux.debian.bugs.dist
From: david@kalnischkies.de

Package: dpkg-dev
Version: 1.22.6
Severity: normal
X-Debbugs-Cc: debhelper@packages.debian.org

Hi,

since recently my arch:any package `ycmd` fails to built from source in
a fresh unstable sbuild environment with at least dpkg 1.22.6 and
debhelper 13.15.2 (compat 13) while generating the dbgsym package:

| dh_gencontrol -O--sourcedirectory=/<<BUILDDIR>>/ycmd-0\+20231230\+git9e43034\+ds/cpp -O--builddirectory=/<<BUILDDIR>>/ycmd-0\+20231230\+git9e43034\+ds/ycm_build
| dpkg-gencontrol: warning: can't parse dependency ycmd-core-version (= )
| dpkg-gencontrol: warning: Depends field of package ycmd: substitution variable ${misc:Depends} used, but is not defined
| dpkg-gencontrol: warning: Depends field of package ycmd: substitution variable ${python3:Depends} used, but is not defined
| dpkg-gencontrol: warning: Depends field of package ycmd: substitution variable ${shlibs:Depends} used, but is not defined
| dpkg-gencontrol: warning: Recommends field of package ycmd: substitution variable ${misc:Clang-Ver} used, but is not defined
| dpkg-gencontrol: warning: Provides field of package ycmd: substitution variable ${misc:Core-Ver} used, but is not defined
| dpkg-gencontrol: warning: can't parse dependency ycmd-core-version (= )
| dpkg-gencontrol: error: parsing package 'ycmd' Provides field: ycmd-core-version (= ), ycmd-core-version (= 48)
| dh_gencontrol: error: dpkg-gencontrol -pycmd -ldebian/changelog -T/dev/null -Pdebian/.debhelper/ycmd/dbgsym-root -UPre-Depends -URecommends -USuggests -UEnhances -UProvides -UEssential -UConflicts -DPriority=optional -UHomepage -UImportant -DAuto-Built-
Package=debug-symbols -UProtected -UBuilt-Using -UStatic-Built-Using -DPackage=ycmd-dbgsym "-DDepends=ycmd (= \${binary:Version})" "-DDescription=debug symbols for ycmd" -DBuild-Ids=dc609a05ca957392f347883f157f1d84a1561dbe -DSection=debug -UMulti-Arch -
UReplaces -UBreaks returned exit code 25
| dh_gencontrol: error: Aborting due to earlier error
| make: *** [debian/rules:19: binary] Error 25

(`vim-youcompleteme` also from me uses something similar but doesn't
fail to build – that one is arch:all and doesn't have a -dbgsym)


The incorrect syntax comes from debian/control containing:
| Provides: ycmd-core-version (= ${misc:Core-Ver}), […]
and dpkg-gencontrol being called with -T/dev/null here (by debhelper).


I am not quite sure if dpkg or debhelper caused this regression with the
recent changes around substvars, but given that a substvar can only be
used to modify the contents of a field and can not embed other fields
in the modification it seems reasonable that if a field is removed from
the output with -U (or overridden with -D) dpkg-gencontrol should not
insist on its syntax being correct – or even warn about undefined
substvars within – as it will have no effect on the output and as
such this might be considered a feature request potentially fixing
a regression (and is as such upgraded from wishlist to normal):

I could easily resolve this error & ignoring the warnings by letting
the entire provides being generated instead of just the version number
here as a simple workaround, but given the choice I would prefer what
I have and it doesn't seem that strange, so others might be effected.


That might very well be a bug in debhelper (too), as I assume it does
this dance to have some fields copied from the package to its -dbgsym offspring, which could contain substvars and hence the -T/dev/null might
be the regression here, but I am not sure as I did not dare too look too
deeply under the hood (or in version control) for the time being.


On a sidenote, while writing this, using "misc:Core-Ver" seems silly…
but deb-substvars(5) doesn't seem to offer a hint at a reasonable naming
scheme less likely to conflict with future changes. Other packages use "<srcname>:<foo>" which seems more reasonable at a glance, so might that
be a good suggestion that could be added there?


Best regards

David Kalnischkies

P.S.: I do consider my sbuild setup reasonably normal/standard, so
I spare you the details, but I am happy to add them if it turns out
I am more of a unique snowflake here than I am assuming.

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