This is a _very_ early, minimal plumbing of the execution graph builder
into the experimental planning engine.
The goal here is mainly just to prove the idea that the planning engine can
build execution graphs using the execgraph.Builder API we currently have.
This implementation is not complete yet, and also we are expecting to
rework the structure of the planning engine later on anyway so this initial
work focuses on just plumbing it in to what we had as straightforwardly
as possible.
This is enough to get a serialized form of _an_ execution graph included
in the generated plan, though since we don't have the apply engine
implemented we don't actually use it for anything yet.
In subsequent commits we'll continue building out the graph-building logic
and then arrange for the apply phase to unmarshal the saved execution graph
and attempt to execute it, so we can hopefully see a minimal version of all
of this working end-to-end for the first time. But for now, this was mainly
just a proof-of-concept of building an execution graph and capturing it
into its temporary home in the plans.Plan model.
Signed-off-by: Martin Atkins <mart@degeneration.co.uk>
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