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.
mergeBody is a hcl.Body implementation that deals with our override file
merging behavior for the portions of the configuration that are not
processed until full eval time.
Mimicking the behavior of our old config merge implementation from the
"config" package, the rules here are:
- Attributes in the override body hide attributes of the same name in
the base body.
- Any block in the override body hides all blocks with the same type name
that appear in the base body.
This is tested by a new test for the overriding of module arguments, which
asserts the correct behavior of the merged body as part of its work.
Some of the fields in our config structs are either mandatory in primary
files or there is a default value that we apply if absent.
Unfortunately override files impose the additional constraint that we
be allowed to omit required fields (which have presumably already been
set in the primary files) and that we are able to distinguish between a
default value and omitting a value entirely.
Since most of our fields were already acceptable for override files, here
we just add some new fields to deal with the few cases where special
handling is required and a helper function to disable the "Required" flag
on attributes in a given schema.
configs.Parser is the entry-point for this package, providing functions to
load and parse HCL-based configuration files.
We use the library "afero" to decouple the parser from the physical OS
filesystem, which here allows us to easily use an in-memory filesystem
for testing and will, in future, allow us to read files from more unusual
places, such as configuration embedded in a plan file.
Martin Atkins