According to documentation (and portage-2.1 behavior), the --fetch-all-uri (-F) flag for emerge is supposed to make it "Instead of doing any package building, just perform fetches for all packages (fetch everything in SRC_URI regardless of USE setting)." However, with portage-2.2_rc5, it seems emerge ignores --fetch-all-uri and continues into the build phase for the package.
Created attachment 161892 [details, diff] fix --fetch-all-uri breakage If this patch is saved as /tmp/fetch_all_uri.patch, then it can be applied as follows: cd /usr/lib/portage patch -p0 < /tmp/fetch_all_uri.patch
This is fixed in 2.2_rc6.