File attributes not considered in cache key calculations (workspaces & local sources)
For both workspaces and local sources we use a recursive directory walk to generate a cache key with the content of files found in those directories and their respective filenames.
Currently we dont take file attributes into account, which is wrong because you want file executable-ness and such to effect your cache key and cause a rebuild. It's also tricky because you wouldnt want file mtimes to effect the build; and it's unclear if we can get into xattrs, and if we do have xattrs; they would have to only be used where xattrs exist.
Considering xattrs, they could be considered on linux but at the same time it's unclear if a buildstream project (i.e. containing a local source data) can be revisioned with something that will recall the xattrs (does git ?).