>=dconf-0.30.1 uses features from meson-0.50.0 but checks for minimal of 0.47.0
from the build log:
Configuring config.h using configuration
Compiler for C supports arguments -fvisibility=hidden: YES
WARNING: Project targetting '>= 0.47.0' but tried to use feature introduced in '0.50.0': install arg in configure_file
Configuring ca.desrt.dconf.service using configuration
Found pkg-config: /usr/bin/x86_64-pc-linux-gnu-pkg-config (0.29.2)
Program abicheck.sh found: YES (/var/tmp/portage/gnome-base/dconf-0.31.2/work/dconf-0.31.2/gsettings/abicheck.sh)
Run-time dependency vapigen found: YES 0.42.7
Program xsltproc found: YES (/usr/bin/xsltproc)
Library dl found: YES
Library m found: YES
Program python3 found: YES (/usr/bin/python3)
Program dbus-daemon found: YES (/usr/bin/dbus-daemon)
Program test-dconf.py found: YES (/var/tmp/portage/gnome-base/dconf-0.31.2/work/dconf-0.31.2/tests/test-dconf.py)
Program meson_post_install.py found: YES (/usr/bin/python3.6 /var/tmp/portage/gnome-base/dconf-0.31.2/work/dconf-0.31.2/meson_post_install.py)
Build targets in project: 28
WARNING: Project specifies a minimum meson_version '>= 0.47.0' but uses features which were added in newer versions:
* 0.50.0: {'install arg in configure_file'}
Found ninja-1.8.2 at /usr/bin/ninja
>>> Source configured.
I'm on meson-0.51.2, so it doesn't affect me, but you might want to fix this before your next release?