Create onbuild variant that runs swift build and potentially executes the output

[swizzlr]

cf. docker-library/python#77

Perhaps this could work?

ONBUILD COPY Package.swift /code/
ONBUILD RUN swift build -c release # cache dependency build artefacts
ONBUILD COPY Sources /code/
ONBUILD RUN swift build -c release # specify destination for output binary
CMD # predefined output binary

[johnlinvc]

I successfully built a simple hello world package with following onbuild setup.

FROM swift:3.0.2
WORKDIR /code
ONBUILD COPY Package.swift /code/
ONBUILD RUN swift build -c release # cache dependency build artefacts
ONBUILD COPY Sources /code/
ONBUILD RUN swift build -c release # specify destination for output binary
CMD ["/bin/bash", "-c", "find .build -executable -type f -not -name '*.so' | head | bash"]

the CMD will find the first non .so built executable and run it.

[swizzlr]

Could you propose that as a PR?

[swizzlr]

Closing per deprecation of onbuild in official images.