Two mechanisms, matching what the make engine actually did:
Lazy defaults. A stack setting is a function myos_default_<VAR>, called only
when the variable has no value, and called again at every reference. That is
exactly a recursive ?=: an explicit value wins, and the default follows a
DOMAIN that a .env changes later. The prefix is what makes it safe; the first
version used a bare function named after the variable, and the test suite
caught it running /usr/bin/host for a stack group called host.
Templates. myos env-update fills a .env from the .env.dist files, expanding
${VAR} against the current values and running $(command), forward references
included.
Also fixed: the project .env now wins over /etc/conf.d/myos, which is what the
documentation claimed and the code did not.
share/make/shim.mk lets a project keep make as a front end: every myos command
becomes a target that shells out to bin/myos, and the project keeps its own
targets and its stack .mk files. It sits outside make/ because the legacy
engine globs every .mk in there.
Setting IFS to a newline to pass the environment also stopped the command
line from splitting, so '-f a -f b' went out as a single argument and the two
words 'docker compose' were looked up as one program name. Every real command
was broken; only --dry-run, which prints a string, looked right.
The variables are now exported in a subshell instead of going through env(1),
which keeps values with spaces intact and leaves the command line to normal
word splitting.
The tests only checked what --dry-run printed, which is why they missed it.
spec/unit/compose_spec.sh now asserts the argv that is actually executed, for
both the plugin and the standalone binary.
Yann Autissier