Make ioc -m/--macros independent of -d/--database order

[jacquelinegarrahan]

Make ioc -m/--macros independent of -d/--database order

Branch: fix/ioc-macros-arg-order → master

Summary

src/python/epicscorelibs/ioc.py main() used a custom argparse action that
snapshotted ns.macros at the moment each -d was parsed:

class DbAction(argparse.Action):
    def __call__(self, parser, ns, values, opt):
        ns.database.append((values, ns.macros))

argparse processes arguments left-to-right, so the macros only took effect for
-d options that appeared after -m. That means:

-m macro=value -d db.db     # works: db loaded with macro=value
-d db.db -m macro=value     # BROKEN: db loaded with EMPTY macros

The broken order is exactly the usage documented in this module:

# Run with python -m epicscorelibs.ioc -d /path/to/db -m macro=value,macro2=value2

so the documented command silently loads the database with no macro
substitution.

Fix

Collect database paths with a plain action='append' and pair each with the
parsed args.macros after parsing, so a single -m applies to every -d
regardless of order:

parser.add_argument('-d', '--database', default=[], action='append', ...)
args = parser.parse_args()
dbs = [(database, args.macros) for database in args.database]
start_ioc(dbs=dbs, ...)

Verification

-d x.db -m a=b   ->  [('x.db', 'a=b')]     # documented order now works
-m a=b -d x.db   ->  [('x.db', 'a=b')]     # still works
-m a=b -d x.db -d y.db -> [('x.db','a=b'), ('y.db','a=b')]

ioc.py byte-compiles.

Note / trade-off

The previous per--d snapshotting could in principle assign different macros
to different databases via interleaved -m ... -d ... -m ... -d .... That
behavior was undocumented and worked only in one direction; this change makes a
single -m apply uniformly to all databases, matching the documented CLI. If
per-database macro sets are ever required, that should be a separate, explicit
feature (e.g. -d db=macros).