Only require gstreamer-gl-1.0 if needed by an option
gstreamer-gl-1.0 is tricky to make available on some systems, so only require it if an optional component such as 'gtk4' needs it.
Step-by-step
$ docker run -it debian:11
$ apt-get update -y && apt-get install -y git curl meson pkg-config libssl-dev flex bison
$ curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
$ source "$HOME/.cargo/env"
$ cargo install cargo-c
$ git clone https://gitlab.freedesktop.org/gstreamer/gstreamer.git
$ cd gstreamer
$ meson setup --auto-features=disabled -Dtools=enabled -Dgstreamer:check=enabled -Drs=enabled -Dgst-plugins-rs:fmp4=enabled builddir
Expected
Setup succeeds.
Actual
Setup fails with
subprojects/gst-plugins-rs/meson.build:78:2: ERROR: Dependency 'gstreamer-gl-1.0' is required but not found.
without this fix.