This allows tracking which subproject it came from at the time of
definition, rather than the time of use. As a result, it is no longer
possible for one subproject which knows that another subproject installs
some data files, to expose those data files via its own
declare_dependency.
There are somewhat common, reasonable and legitimate use cases for a
dependency to provide data files installed to /usr which are used as
command inputs. When getting a dependency from a subproject, however,
the attempt to directly construct an input file from a subproject
results in a sandbox violation. This means not all dependencies can be
wrapped as a subproject.
One example is wayland-protocols XML files which get scanned and used to
produce C source files.
Teach Meson to recognize when a string path is the result of fetching a
dep.get_variable(), and special case this to be exempt from subproject
violations.
A requirement of this is that the file must be installed by
install_data() or install_subdir() because otherwise it is not actually
representative of what a pkg-config dependency would provide.
Jussi Pakkanen
Eli Schwartz