docker_build: unintuitive behavior if data_path isn't a prefix of added files' paths

[kamalmarhubi]

If data_path is not a prefix of a file, that file gets inserted with its entire path form the repository root in tact. This can actually be exploited as a workaround for the bazelbuild/bazel#677 : set data_path to some absolute path that's not a prefix of the files you are adding.

[kamalmarhubi]

I think this should be treated as an error. @damienmg thoughts?

[damienmg]

This is working as designed but I have not given much though about what should be the correct behavior, an error might be wanted indeed.

[kamalmarhubi]

As a data point, the analogous strip_prefix on new_http_archive fails if the prefix isn't found in the archive.

[kamalmarhubi]

Actually not quite:

Note that if there are files outside of this directory, they will be discarded and inaccessible (e.g., a top-level license file). This includes files/directories that start with the prefix but are not in the directory (e.g., foo-lib-1.2.3.release-notes). If the specified prefix does not match a directory in the archive, Bazel will return an error.

http://bazel.io/docs/be/workspace.html#new_http_archive

[pcj]

Closing due to age.