Building package with variable in makedepends fails with "Package '$variable': Could not find aport"

I'm trying to build phoc (to add a patch for https://gitlab.gnome.org/World/Phosh/phosh/-/issues/900) and am getting this error:

[20:53:10] ERROR: Package '$_wlrootsmakedepends': Could not find aport, and could not find this package in any APKINDEX!
[20:53:10] See also: <https://postmarketos.org/troubleshooting>
Run 'pmbootstrap log' for details.

The phoc 0.25.0-r0 APKBUILD defines _wlrootsmakedepends and then uses it in defining makedepends, which pmbootstrap doesn't seem to understand:

_wlrootsmakedepends="
	eudev-dev
	# ...
	xwayland-dev
	"
makedepends="
	glib-dev
	# ...
	wayland-protocols
	$_wlrootsmakedepends
	"

Workaround: Copy the content of _wlrootsmakedepends into makedepends. Not pretty, but works.

Defining makedepends using variables doesn't seem to be very common, but a fix would still be nice.

pmbootstrap log

(044545) [20:53:10] ERROR: Package '$_wlrootsmakedepends': Could not find aport, and could not find this package in any APKINDEX!
(044545) [20:53:10] See also: <https://postmarketos.org/troubleshooting>
(044545) [20:53:10] Traceback (most recent call last):
  File "/usr/share/pmbootstrap/pmb/__init__.py", line 49, in main
    getattr(frontend, args.action)(args)
  File "/usr/share/pmbootstrap/pmb/helpers/frontend.py", line 115, in build
    if not pmb.build.package(args, package, arch_package, force,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/share/pmbootstrap/pmb/build/_package.py", line 523, in package
    if not init_buildenv(args, apkbuild, arch, strict, force, cross, suffix,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/share/pmbootstrap/pmb/build/_package.py", line 207, in init_buildenv
    depends, built = build_depends(args, apkbuild, depends_arch, strict)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/share/pmbootstrap/pmb/build/_package.py", line 155, in build_depends
    if package(args, depend, arch, strict=strict):
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/share/pmbootstrap/pmb/build/_package.py", line 514, in package
    apkbuild = get_apkbuild(args, pkgname, arch)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/share/pmbootstrap/pmb/build/_package.py", line 52, in get_apkbuild
    raise RuntimeError("Package '" + pkgname + "': Could not find aport, and"
RuntimeError: Package '$_wlrootsmakedepends': Could not find aport, and could not find this package in any APKINDEX!