debian/install had the strange property that you had to leave leading slashes off paths.
Looks like filesets in snapcraft.yaml have the same property.
This makes it annoying to generate those files from variables that have full paths, as snapcraft aborts with
Failed to load plugin: path “/foo” must be relative
Can you please ignore the leading slash if present (possibly with a warning)?
I brought this up two years ago but don’t recall getting an answer: