So there are some competing expectations here. The status quo is that
non-interactive invocations of 'guix shell' will not load a guix.scm or
manifest.scm file unless explicitly told to via --file/--manifest following
the "explicit is better than implicit" philosophy.  People like myself who
almost exclusively invoke 'guix shell' without any arguments would expect
that 'guix shell -- make' would load their guix.scm file like they're used
to.  It is the latter expectation that is typically the status quo in other
language environments.  For example, in Ruby land, 'bundle exec foo' runs
the command 'foo' non-interactively in the context of a project and you
don't have to tell it where to find the conventional Gemfile because it's
the default.  Treating interactive and non-interactive invocation
differently in 'guix shell' was a surprise for me.  Of course, 'guix shell
-D -f guix.scm -- make' works, but it doesn't "just work."  Both viewpoints
have their merits and I'm wondering if there's a way to satisfy both
expectations.  Perhaps 'guix shell -- make' would load guix.scm, but 'guix
shell --pure -- make', or any invocation with any flags, would not?  Or,
less ideal, a new short flag that can be passed that would be the
equivalent of `-D -f guix.scm` (or the manifest.scm variant) to at least
make for less typing.  Personally, I think that defaulting to loading from
a conventional file when no packages are specified is much more user
friendly than generating an empty profile, regardless of interactive vs.
non-interactive.

Thoughts?

- Dave