In the very first implementation of "sensitive values" we were
unfortunately not disciplined about separating the idea of "marked value"
from the idea of "sensitive value" (where the latter is a subset of the
former). The first implementation just assumed that any marking whatsoever
meant "sensitive".
We later improved that by adding the marks package and the marks.Sensitive
value to standardize on the representation of "sensitive value" as being
a value marked with _that specific mark_.
However, we did not perform a thorough review of all of the mark-handling
codepaths to make sure they all agreed on that definition. In particular,
the state and plan models were both designed as if they supported arbitrary
marks but then in practice marks other than marks.Sensitive would be
handled in various inconsistent ways: dropped entirely, or interpreted as
if marks.Sensitive, and possibly do so inconsistently when a value is
used only in memory vs. round-tripped through a wire/file format.
The goal of this commit is to resolve those oddities so that there are now
two possible situations:
- General mark handling: some codepaths genuinely handle marks
generically, by transporting them from input value to output value in
a way consistent with how cty itself deals with marks. This is the
ideal case because it means we can add new marks in future and assume
these codepaths will handle them correctly without any further
modifications.
- Sensitive-only mark preservation: the codepaths that interact with our
wire protocols and file formats typically have only specialized support
for sensitive values in particular, and lack support for any other
marks. Those codepaths are now subject to a new rule where they must
return an error if asked to deal with any other mark, so that if we
introduce new marks in future we'll be forced either to define how we'll
avoid those markings reaching the file/wire formats or extend the
file/wire formats to support the new marks.
Some new helper functions in package marks are intended to standardize how
we deal with the "sensitive values only" situations, in the hope that
this will make it easier to keep things consistent as the codebase evolves
in future.
In practice the modules runtime only ever uses marks.Sensitive as a mark
today, so all of these checks are effectively covering "should never
happen" cases. The only other mark Terraform uses is an implementation
detail of "terraform console" and does not interact with any of the
codepaths that only support sensitive values in particular.
The state serialization only knows how to save and restore the
marks.Sensitive mark in particular, but previously it was just assuming
that any mark it found was sensitive without actually checking.
Now we'll return an error if we're asked to save a mark we don't support.
In practice there are no other marks currently used by the modules runtime
and so this cannot fail, but this is to help notice problems sooner if we
introduce any new marks later.
Instances of the same AbsResource may share the same Dependencies, which
could point to the same backing array of values. Since address values
are not pointers, and not meant to be shared, we must copy the value
before sorting the slice in-place. Because individual instances of the
same resource may be encoded to state concurrently, failure to copy the
slice first can result in a data race.
The specific output order is meaningless, but it should always be the same after
two Encode() calls with identical (ignoring in-memory order) dependency sets.
