In study of existing providers we've found a pattern we werent previously
accounting for of using a nested block type to represent a group of
arguments that relate to a particular feature that is always enabled but
where it improves configuration readability to group all of its settings
together in a nested block.
The existing NestingSingle was not a good fit for this because it is
designed under the assumption that the presence or absence of the block
has some significance in enabling or disabling the relevant feature, and
so for these always-active cases we'd generate a misleading plan where
the settings for the feature appear totally absent, rather than showing
the default values that will be selected.
NestingGroup is, therefore, a slight variation of NestingSingle where
presence vs. absence of the block is not distinguishable (it's never null)
and instead its contents are treated as unset when the block is absent.
This then in turn causes any default values associated with the nested
arguments to be honored and displayed in the plan whenever the block is
not explicitly configured.
The current SDK cannot activate this mode, but that's okay because its
"legacy type system" opt-out flag allows it to force a block to be
processed in this way anyway. We're adding this now so that we can
introduce the feature in a future SDK without causing a breaking change
to the protocol, since the set of possible block nesting modes is not
extensible.
Nulls can't exist in HCL, and the legacy sdk will panic when
encountering them. The map shim already did this, just copy the same
pattern in the list case.
This reverts commit 3677522a28.
Later changes negate the need for this, and removing these again
prevents us from having to strip them back out when helper/schema
doesn't want them.
This is a more specialized version of ConfigValueFromHCL2 which is
specifically for config values that represent the content of a block
body in the configuration.
By using the schema of that block we can more precisely emulate the old
HCL1/HIL behaviors by distinguishing attributes from blocks and applying
some slightly different behaviors for the handling of null values and
of empty collections that are representing the absense of blocks of a
particular type.
Absent values are omitted by the old code we are emulating in HCL, so we
must do the same here in order to avoid breaking assumptions in the
helper/schema layer.
The value-conversion machinery is also needed in the main "terraform"
package to help us populate our HCL2 evaluation scope, so a subset of the
shim functions move here into a new package where they can be public.
Some of them remain private within the config package since they depend
on some other symbols in the config package, and they are not needed
by outside callers anyway.
Martin Atkins