We want the forthcoming v0.12.0 release to be the last significant
breaking change to our main configuration constructs for a long time, but
not everything could be implemented in that release.
As a compromise then, we reserve various names we have some intent of
using in a future release so that such future uses will not be a further
breaking change later.
Some of these names are associated with specific short-term plans, while
others are reserved conservatively for possible later work and may be
"un-reserved" in a later release if we don't end up using them. The ones
that we expect to use in the near future were already being handled, so
we'll continue to decode them at the config layer but also produce an
error so that we don't get weird behavior downstream where the
corresponding features don't work yet.
In our new loader we are changing certain values in configuration to be
naked keywords or references rather than quoted strings as before. Since
many of these have been shown in books, tutorials, and our own
documentation we will make the old forms generate deprecation warnings
rather than errors so that newcomers starting from older documentation
can be eased into the new syntax, rather than getting blocked.
This will also avoid creating a hard compatibility wall for reusable
modules that are already published, allowing them to still be used in
spite of these warnings and then fixed when the maintainer is able.
This is a first pass of decoding of the main Terraform configuration file
format. It hasn't yet been tested with any real-world configurations, so
it will need to be revised further as we test it more thoroughly.
Martin Atkins