$ swift package --version
Apple Swift Package Manager - Swift 3.0.2 (swiftpm-11750)

cd Foo/
swift package init
git init .
git add .
git commit -a -m "initial version"
git tag -a 1.0.0 HEAD -m 1.0.0
vim Sources/Foo.swift # make any change
git commit -a -m "foo change"
git tag -a 1.0.0-6-gdeadbeef HEAD -m 1.0.0-6-gdeadbeef

cd ../Bar
swift package init
vim Package.swift # add Foo at 1.0.0-6-gdeadbeef as a dependency
swift build # note output says "Resolved version: 1.0.0"
ls Packages/ # see version was resolved to 1.0.0 instead of 1.0.0-6-gdeadbeef