People with `uuid()` usage in their configurations would receive shadow
errors every time on plan because the UUID would change.
This is hacky fix but I also believe correct: if a shadow error contains
uuid() then we ignore the shadow error completely. This feels wrong but
I'll explain why it is likely right:
The "right" feeling solution is to create deterministic random output
across graph runs. This would require using math/rand and seeding it
with the same value each run. However, this alone probably won't work
due to Terraform's parallelism and potential to call uuid() in different
orders. In addition to this, you can't seed crypto/rand and its unlikely
that we'll NEVER use crypto/rand in the future even if we switched
uuid() to use math/rand.
Therefore, the solution is simple: if there is no shadow error, no
problem. If there is a shadow error and it contains uuid(), then ignore
it.
dag.Graph is used as a value, but contains a sync data structure. This
prevents copying the value, and is needed if one wants to upgrade a Graph
to an AcyclicGraph.
The sync.Once only guards the init() method, which can be guarded
internally with nil checks on the fields. The init method could be
removed entirely with a proper constructor later on of we so choose.
The AnnotateVertex and AnnotateEdge Graph methods will allow terraform
to insert arbitray information into the encoded graph stream for later
processing.
The external api provided here is simply
dag.Graph.SetDebugWriter(io.Writer). When a writer is provided to a
Graph, it will immediately encode itself to the stream, and subsequently
encode any additional transformations to the graph. This will allow
easier logging of graph transformations without writing complete graphs
to the logs at every step. Since the marshalGraph can also be dot
encoded, this will allow translation from the JSON logs to dot graphs.
To maintain the same output, the Graph.Dot implementation needs to be
aware of GraphNodeDotter. Copy the interface into the dag package, and
make the Dot marshaler aware of which nodes implemented the interface.
This way we can remove most of the remaining dot code from terraform.
The dot format generation was done with a mix of code from the terraform
package and the dot package. Unify the dot generation code, and it into
the dag package.
Use an intermediate structure to allow a dag.Graph to marshal itself
directly. This structure will be ablt to marshal directly to JSON, or be
translated to dot format. This was we can record more information about
the graph in the debug logs, and provide a way to translate those logged
structures to dot, which is convenient for viewing the graphs.
This fixes: `TestContext2Apply_moduleDestroyOrder`
The new destroy graph wasn't properly creating edges that happened
_through_ an output, it was only created the edges for _direct_
dependents.
To fix this, the DestroyEdgeTransformer now creates the full transitive
list of destroy edges by walking all ancestors. This will create more
edges than are necessary but also will no longer miss resources through
an output.
