There is some note here
https://mesonbuild.com/Subprojects.html
or here
https://blogs.gnome.org/ignatenko/2015/05/21/meson-and-3rd-p...
Or more recently with Bazel that do the same but arrives to do it much worst:
https://github.com/tensorflow/tensorflow/issues/6210
or
https://archive.fosdem.org/2018/schedule/event/how_to_make_p...
Same with Hunter and CMake External:
https://github.com/ruslo/hunter/issues/296
I have managed an ecosystem of ~250 software for a team in the past.
Software bundling their dependencies are the worst and any package manager will tell you that.
Due to diamond dependency problem, they explode as soon as you try to integrate them into a bigger picture... It is a pure waste of time for every packager.
And I am not even speaking of bug fixes update on dependencies, security update, environment without Internet access or anything like that.... because dependency bundling prevent or make hard all of that.