$ emerge -1 astal-gtk

These are the packages that would be merged, in order:

Calculating dependencies... done!
Dependency resolution took 1.66 s (backtrack: 0/20).

[ebuild  N     ] gui-apps/astal-io-1.0
[ebuild  N     ] gui-apps/astal-gtk-1.0

Would you like to merge these packages? [Yes/No] Yes
>>> Verifying ebuild manifests
>>> Emerging (1 of 2) gui-apps/astal-io-1.0::gdldg-gentoo-overlay
>>> Failed to emerge gui-apps/astal-io-1.0, Log file:
>>>  '/var/tmp/portage/gui-apps/astal-io-1.0/temp/build.log'
>>> Jobs: 0 of 2 complete, 1 failed              Load avg: 1.64, 1.65, 1.71
 * Package:    gui-apps/astal-io-1.0:0
 * Repository: gdldg-gentoo-overlay
 * USE:        abi_x86_64 amd64 elibc_glibc kernel_linux
 * FEATURES:   network-sandbox preserve-libs sandbox userpriv usersandbox
>>> Unpacking source...
 * Repository id: aylur_astal.git
 * To override fetched repository properties, use:
 *   EGIT_OVERRIDE_REPO_AYLUR_ASTAL
 *   EGIT_OVERRIDE_BRANCH_AYLUR_ASTAL
 *   EGIT_OVERRIDE_COMMIT_AYLUR_ASTAL
 *   EGIT_OVERRIDE_COMMIT_DATE_AYLUR_ASTAL
 *
 * Fetching https://github.com/aylur/astal.git ...
git fetch https://github.com/aylur/astal.git +HEAD:refs/git-r3/HEAD
git symbolic-ref refs/git-r3/gui-apps/astal-io/0/__main__ refs/git-r3/HEAD
 * Checking out https://github.com/aylur/astal.git to /var/tmp/portage/gui-ap
ps/astal-io-1.0/work/astal-io-1.0 ...
git checkout --quiet refs/git-r3/HEAD
GIT update -->
   repository:               https://github.com/aylur/astal.git
   at the commit:            956b74fd9ff8c607b6683b404860c4e6b30ffe2b
>>> Source unpacked in /var/tmp/portage/gui-apps/astal-io-1.0/work
>>> Preparing source in /var/tmp/portage/gui-apps/astal-io-1.0/work/astal-io-
1.0 ...
/var/tmp/portage/gui-apps/astal-io-1.0/temp/environment: line 3388: vala_src_
prepare: command not found
>>> Source prepared.
>>> Configuring source in /var/tmp/portage/gui-apps/astal-io-1.0/work/astal-i
o-1.0 ...
meson setup -Db_lto=false --libdir lib64 --localstatedir /var/lib --prefix /u
sr --sysconfdir /etc --wrap-mode nodownload --build.pkg-config-path /usr/shar
e/pkgconfig --pkg-config-path /usr/share/pkgconfig --native-file /var/tmp/por
tage/gui-apps/astal-io-1.0/temp/meson.x86_64-pc-linux-gnu.amd64.ini -Db_pch=f
alse -Dwerror=false -Dbuildtype=plain /var/tmp/portage/gui-apps/astal-io-1.0/
work/astal-io-1.0 /var/tmp/portage/gui-apps/astal-io-1.0/work/astal-io-1.0-bu
ild

ERROR: Neither source directory '/var/tmp/portage/gui-apps/astal-io-1.0/work/astal-io-1.0' nor build directory '/var/tmp/portage/gui-apps/astal-io-1.0/work/astal-io-1.0-build' contain a build file meson.build.
 * ERROR: gui-apps/astal-io-1.0::gdldg-gentoo-overlay failed (configure phase):
 *   configure failed
 *
 * Call stack:
 *     ebuild.sh, line  136:  Called src_configure
 *   environment, line 3379:  Called meson_src_configure
 *   environment, line 2644:  Called die
 * The specific snippet of code:
 *       [[ ${rv} -eq 0 ]] || die -n "configure failed";
 *
 * If you need support, post the output of `emerge --info '=gui-apps/astal-io-1.0::gdldg-gentoo-overlay'`,
 * the complete build log and the output of `emerge -pqv '=gui-apps/astal-io-1.0::gdldg-gentoo-overlay'`.
 * The complete build log is located at '/var/tmp/portage/gui-apps/astal-io-1.0/temp/build.log'.
 * The ebuild environment file is located at '/var/tmp/portage/gui-apps/astal-io-1.0/temp/environment'.
 * Working directory: '/var/tmp/portage/gui-apps/astal-io-1.0/work/astal-io-1.0'
 * S: '/var/tmp/portage/gui-apps/astal-io-1.0/work/astal-io-1.0'

 * Messages for package gui-apps/astal-io-1.0:

 * ERROR: gui-apps/astal-io-1.0::gdldg-gentoo-overlay failed (configure phase):
 *   configure failed
 *
 * Call stack:
 *     ebuild.sh, line  136:  Called src_configure
 *   environment, line 3379:  Called meson_src_configure
 *   environment, line 2644:  Called die
 * The specific snippet of code:
 *       [[ ${rv} -eq 0 ]] || die -n "configure failed";
 *
 * If you need support, post the output of `emerge --info '=gui-apps/astal-io-1.0::gdldg-gentoo-overlay'`,
 * the complete build log and the output of `emerge -pqv '=gui-apps/astal-io-1.0::gdldg-gentoo-overlay'`.
 * The complete build log is located at '/var/tmp/portage/gui-apps/astal-io-1.0/temp/build.log'.
 * The ebuild environment file is located at '/var/tmp/portage/gui-apps/astal-io-1.0/temp/environment'.
 * Working directory: '/var/tmp/portage/gui-apps/astal-io-1.0/work/astal-io-1.0'
 * S: '/var/tmp/portage/gui-apps/astal-io-1.0/work/astal-io-1.0'