The set of paths which caused a resource update to require replacement
has been stored in the plan since 0.15.0 (#28201). This commit adds a
simple JSON representation of these paths, allowing consumers of this
format to determine exactly which paths caused the resource to be
replaced.
This representation is intentionally more loosely encoded than the JSON
state serialization of paths used for sensitive attributes. Instead of a
path step being represented by an object with type and value, we use a
more-JavaScripty heterogenous array of numbers and strings. Any
practical consumer of this format will likely traverse an object tree
using the index operator, which should work more easily with this
format. It also allows easy prefix comparison for consumers which are
tracking paths.
While updating the documentation to include this new field, I noticed
that some others were missing, so added them too.
Previously we were repeating some logic in the UI layer in order to
recover relevant additional context about a change to report to a user.
In order to help keep things consistent, and to have a clearer path for
adding more such things in the future, here we capture this user-facing
idea of an "action reason" within the plan model, and then use that
directly in order to decide how to describe the change to the user.
For the moment the "tainted" situation is the only one that gets a special
message, matching what we had before, but we can expand on this in future
in order to give better feedback about the other replace situations too.
This also preemptively includes the "replacing by request" reason, which
is currently not reachable but will be used in the near future as part of
implementing the -replace=... plan command line option to allow forcing
a particular object to be replaced.
So far we don't have any special reasons for anything other than replacing,
which makes sense because replacing is the only one that is in a sense
a special case of another action (Update), but this could expand to
other kinds of reasons in the future, such as explaining which of the
few different reasons a data source read might be deferred until the
apply step.
Alisdair McDiarmid