The raw plan output changes were stored in the output exec node, when
they should have instead been fetch lazily through the context via the
synchronized ChangesSync value.
We had intended these functions to attempt to convert any given value, but
there is a special behavior in the function system where functions must
opt in to being able to handle dynamically-typed arguments so that we
don't need to repeat the special case for that inside every function
implementation.
In this case we _do_ want to specially handle dynamically-typed values,
because the keyword "null" in HCL produces
cty.NullVal(cty.DynamicPseudoType) and we want the conversion function
to convert it to a null of a more specific type.
These conversion functions are already just a thin wrapper around the
underlying type conversion functionality anyway, and that already supports
converting dynamic-typed values in the expected way, so we can just opt
in to allowing dynamically-typed values and let the conversion
functionality do the expected work.
Fixing this allows module authors to use type conversion functions to
give additional type information to Terraform in situations that are too
ambiguous to be handled automatically by the type inference/unification
process. Previously tostring(null) was effectively a no-op, totally
ignoring the author's request to treat the null as a string.
replace_triggered_by references are scoped to the current module, so we
need to filter changes for the current module instance. Rather than
creating a ConfigResource and filtering the result, make a
Changes.InstancesForAbsResource method to get only the AbsResource
changes.
Check for triggered resource replacement in the plan. While the
functionality of the feature works here, we ill want to follow up with a
way to indicate in the plan _why_ the resource was replaced.
The EvalContext is the only place with all the information to be able to
complete the evaluation of the replace_triggered_by expressions. These
need to be evaluated into a reference, which is then looked up in the
pending changes which the context has access too. On top of needing the
plan changes, we also need access to all providers and schemas to decode
the changes if we need to traverse the resource values for individual
attributes.
