Adds a few unbinds to prevent bad joins from occurring.
Firstly, we never want to join `StepSummary::step` with
`TypeTracker::append` on `summary` as the first join, as the resulting
relation is absolutely massive. So we decouple the two occurrences of
`summary` by unbinding each of them.
Secondly, in some cases the node we're stepping to (`nodeTo` for type
trackers, `nodeFrom` for type backtrackers) will get joined eagerly
with the typetracker one is defining, and again this produces an
uncomfortably large intermediate join. A bit of unbinding prevents this
as well.
This requires a bit of explanation, so strap in.
Firstly, because we use `LocalSourceNode`s as the start and end points
of our `StepSummary::step` relation, there's no need to include
`simpleLocalFlowStep` (via `typePreservingStep`) in `smallstep`. Indeed,
since the successor node for a `step` is a `LocalSourceNode`, and local
sources never have incoming flow, this is entirely futile -- we can find
values for `mid` and `nodeTo` that satisfy the body of `step`, but
`nodeTo` will never be a `LocalSourceNode`.
With this in mind, we can simplify `smallstep` to only refer to
`jumpStep`.
This then brings the other uses of `typePreservingStep` into question.
The only other place we use this predicate is in the `TypeTracker` and
`TypeBackTracker` `smallstep` predicates. Note, however, that here we
no longer need `jumpStep` to be part of `typeTrackingStep` (as it is
already accounted for in `StepSummary::smallstep`) so we can simplify
to `simpleLocalFlowStep`. At this point, `typePreservingStep` is unused.
Finally, because of the way `smallstep` is used in `step` (inside
`StepSummary`), `nodeTo` must always be a `LocalSourceNode`, so I have
propagated this restriction to `smallstep` as well. We can always lift
this restriction later, but for now it seems like it's likely to cause
fewer surprises to have made this explicit.
Moves the `flowsTo` logic into the shared implementation, so that
`TypeTrackingPrivate` only has to define the shape of immediate store
steps.
Also cleans up the documentation to talk a bit more about what
`content` can represent, and what caveats there are.
There seems to have been some cases where the old ones have been picked up
instead of the new ones. At least I spotted _one_ case where this happened, in
an internal actions run.
I'm not sure how to actual debug this, so just removing all the tags that could
make these queries to become picked up :|
instead of points-to.
Looking at query results also made me realize I didn't supply a very good
"origin" for ECC in cryptography package, so I improved that 👍 -- maybe that
sohuld have been split into multiple commits... too late :(
