docker build should not require any "prereq" steps like building the wheel on the host machine

[Thomas Gilgenast]

we would normally assume that you can git clone and then immediately docker build . but this assumption is currently being violated

this can be easily solved by making the existing image a “second stage“ and adding a first stage whose job it is to build the wheel

the $VERSION build arg only needs to be passed to the first stage - version information will be stored in the wheel after the first stage builds and the second stage can copy dist/*.whl from the builder to /install in the second stage and then pip install /install/*.whl

the end of this post has a good example of how to do this

[Thomas Gilgenast]

we have some preliminary progress on this in 7b2e46b

to add back version information, we are considering using setuptools-scm instead of versioneer (versioneer is no longer maintained) since setuptools-scm appears to allow overriding the git-determined version via a simple SETUPTOOLS_SCM_PRETEND_VERSION environment variable

a second problem to solve is that the app code gets copied to the builder image before the dependency wheels get copied to and installed in the final image - this means that the dep copy and dep install (but not dep build) steps will be repeated every time app code changes

[Thomas Gilgenast]

we solved the second of these two problems in f1ebfe5

[Thomas Gilgenast]

finally fixes #67

in this commit, we switched out versioneer for setuptools-scm

this allows us to override the version information inside the docker image using a SETUPTOOLS_SCM_PRETEND_VERSION environment variable

using setuptools-scm requires us to be more picky about how we control the inclusion of files into our sdists via MANIFEST.in

we also incur a dependency on importlib_metadata, a pre-3.8 backport of importlib.metadata

→ <<cset af1acbd89646>>