These new functions allow Terraform to be used for network address space
planning tasks, and make it easier to produce reusable modules that
contain or depend on network infrastructure.
For example:
- cidrsubnet allows an aws_subnet to derive its
CIDR prefix from its parent aws_vpc.
- cidrhost allows a fixed IP address for a resource to be assigned within
an address range defined elsewhere.
- cidrnetmask provides the dotted-decimal form of a prefix length that is
accepted by some systems such as routing tables and static network
interface configuration files.
The bulk of the work here is done by an external library I authored called
go-cidr. It is MIT licensed and was implemented primarily for the purpose
of using it within Terraform. It has its own unit tests and so the unit
tests within this change focus on simple success cases and on the correct
handling of the various error cases.
There isn't any precedent for abbreviating words in the interpolation
function names, and it may not be clear to all users what "enc" and "dec"
are short for, so instead we'll prefer to spell out the whole words for
improved readability.
Had to handle a lot of implicit leaning on a few properties of the old
representation:
* Old representation allowed plain strings to be treated as lists
without problem (i.e. shoved into strings.Split), now strings need to
be checked whether they are a list before they are treated as one
(i.e. shoved into StringList(s).Slice()).
* Tested behavior of 0 and 1 length lists in formatlist() was a side
effect of the representation. Needs to be special cased now to
maintain the behavior.
* Found a pretty old context test failure that was wrong in several
different ways. It's covered by TestContext2Apply_multiVar so I
removed it.
This is the initial pure "all tests passing without a diff" stage. The
plan is to change the internal representation of StringList to include a
suffix delimiter, which will allow us to recognize empty and
single-element lists.
formatlist distributes formatting over lists.
See the docs for details.
As a colleague commented:
"It happens all the time that we want a set of
outputs, but in a slightly different way than
just simple joining or concatting."
formatlist (combined with join)
makes it easy to satisfy those needs.
Mitchell Hashimoto