Created attachment 1225806 [details]
output from 'dnf install @buildsys-build' to an installroot on freshly installed and updated F25 VM

Installing the packages in an installroot with dnf installs all 205 packages, so maybe there's something mock is doing?

# dnf --installroot /root/dnf-test --releasever 25 install @buildsys-build
...
Transaction Summary
=============================================================================================================================
Install  205 Packages

Total download size: 138 M
Installed size: 534 M
...

(see attached file for full logs

I can reproduce it.
mock --scrub=all
mock --init

This seems like it could be a problem if the buildroot ends up missing some important (but optional) dependency that a package relies on, and it isn't explicitly pulled on: i.e. the package is built without libsomefundamentalfeature and automagically configures the feature off.

Here comes full reproducer. Just with DNF (therefore moving to DNF team):

mkdir -p /tmp/3/etc/dnf
# I am attaching this dnf.conf
# but you can create it by: mock -r fedora-24-x86_64 --init
# and it will be created in this location
cp /var/lib/mock/fedora-24-x86_64/root/etc/dnf/dnf.conf /tmp/3/etc/dnf/
# this is what mock is running
sudo /usr/bin/dnf --installroot /tmp/3 --releasever 24 --disableplugin=local --setopt=deltarpm=false install @buildsys-build

For some reason DNF things that some packages are already installed in that installroot. Although there is no rpmdb at all. And no other files but dnf.conf

Reproduced with: dnf-1.1.10-4.fc25.noarch

Created attachment 1231170 [details]
dnf.conf used in the reproducer (standard mock config)

(In reply to Oliver Henshaw from comment #3)
> This seems like it could be a problem if the buildroot ends up missing some
> important (but optional) dependency that a package relies on, and it isn't
> explicitly pulled on: i.e. the package is built without
> libsomefundamentalfeature and automagically configures the feature off.

Indeed, a locally rebuilt systemd-231-10.fc25 (with minor logging patches) loses liblz4.so.1() from its Requires.

(In reply to Miroslav Suchý from comment #5)
> Created attachment 1231170 [details]
> dnf.conf used in the reproducer (standard mock config)

With no dnf.conf:
# /usr/bin/dnf --installroot /tmp/3 --releasever 24 --disableplugin=local --setopt=install_weak_deps=0 --setopt=deltarpm=false install @buildsys-build

reproduces.

(In reply to Oliver Henshaw from comment #6)
> (In reply to Oliver Henshaw from comment #3)
> > This seems like it could be a problem if the buildroot ends up missing some
> > important (but optional) dependency that a package relies on, and it isn't
> > explicitly pulled on: i.e. the package is built without
> > libsomefundamentalfeature and automagically configures the feature off.
> 
> Indeed, a locally rebuilt systemd-231-10.fc25 (with minor logging patches)
> loses liblz4.so.1() from its Requires.

Actually, this looks like it was a fallout from lz4 changing its version numbering scheme (and the new version was released in f25 updates) - https://github.com/systemd/systemd/commit/3d4cf7de48a74726694abbaa09f9804b845ff3ba probably fixes this.

This is basically packages which are newer, but solver choosed to not install them (in this case it doesn't fullfil requirements of systemd).

Trying to reproduce with dnf-2.5.1-1.fc26.noarch
I am not able to reproduce the initial bug. All those packages are installed. But...

sudo rm -rf /tmp/3
mkdir -p /tmp/3/etc/dnf/
mock -r fedora-26-x86_64 --init --no-bootstrap-chroot
cp /var/lib/mock/fedora-26-x86_64/root/etc/dnf/dnf.conf /tmp/3/etc/dnf/
sudo /usr/bin/dnf --installroot /tmp/3 --releasever 26 --disableplugin=local --setopt=deltarpm=false list

gives me full list of packages installed on host and not in specified installroot. It should produce empty list.

For the list command, it is necessary to use --installed option to get only installed packages. With that option I got empty list (dnf-2.5.1-1). Thanks Miroslav a lot for your help and testing.