Currently, if nonzero struct is passed to the DecodeBody function,
decoding process will keep already initialized top-level fields values or
overwrite them, if they are specified in HCL. This behaviour is useful,
as it allows to have some default values for top-level fields.
However, if the field is a type block or slice (multiple blocks), then the
entire block is overwritten, which erases the existing values. Because of
that, setting default values in nested structs is not possible.
With this commit, decode functions will check if the value is
nil and only then set them to empty struct, which allows for appending
to existing structs.
In case of a slice, either new empty element will be added, or existing
element will be used for setting new value (so values will be merged).
Also, to keep the same behavior as json.Unmarshal, if retained list
have more elements than new list, additional elements will be removed
and existing elements will be merged. This allows to have default values
also for positional elements.
Behavior added by this patch is the same as in json.Unmarshal and
yaml.Unmarshal, which both retain nested structs during unmarshaling
process, so I believe this is an expected behavior from user
perspective.
These are wrappers around the lower-level hclwrite package that are able
to reverse a subset of the behavior of the Decode functions to populate
an hclwrite DOM.
They are not fully symmetrical with DecodeBody because that function can
leave certain parts of the configuration in its opaque form for later
decoding, and these encode functions don't have enough information to
repack that abstract/opaque form into new source code.
In practice we expect that callers using complex techniques like partial
decoding will also use more complex techniques with the hclwrite API
directly, since they will need to coordinate partial _encoding_ of data
that has been portioned off into separate structures, which gohcl is not
equipped to do itself.
big.Float is not DeepEqual-friendly because it contains a precision value
that can make two numerically-equal values appear as non-equal.
Since the number decoding isn't the point of these tests, instead we just
swap out for cty.Bool values which _are_ compatible with
reflect.DeepEqual, since they are just wrappers around the native bool
type.
Previously we required optional attributes to be specified as pointers so that we could represent the empty vs. absent distinction.
For applications that don't need to make that distinction, representing "optional" as a struct tag is more convenient.
Rather than writing a nil hcl.Expression, as a special case we'll deal
with this within the cty type system, which we assume is what the caller
wants if they are decoding into a hcl.Expression rather than a native Go
type.
This is a super-invasive update since the "zcl" package in particular
is referenced all over.
There are probably still a few zcl references hanging around in comments,
etc but this takes care of most of it.
The main "zcl" package requires a bit more care because of how many
callers it has and because of its two subpackages, so we'll take care
of that one separately.
