Add a step from that `CfgNode` to the corresponding `EssaNode`.
The intended effect is seen in `ImpliesDataflow.expected`.
The efeect seen in other `.expected`-files is that parameter nodes
change type, that the extra steps are seen, and that flow from
`EssaVar`s is mirrored in flow from `CfgNode`s.
There is one surprise, which is the `.0` node in
`coverage/localFlow.expected`.
I'm slightly suspicious of this fix -- it seems to work, but it makes
me wonder if we're potentially missing other kinds of flow, by not
handling other kinds of definitions.
Also, I feel like this should really be attached to an appropriate
post-update node of the given argument. As it is written now, the flow
will go from the argument _before_ the call, which obviously misses a
step if the argument is modified by the call. In practice, I would
expect this to be rather rare.
This is the quick-and-dirty solution, as discussed.
An even quicker-and-dirtier solution would have used
`ModuleValue::attr` and take the `getOrigin` of that as the source of
the jump step. However, this turns out to be a bad choice, since
`attr` might fail to have a value for the given attribute (for a
variety of reasons). Thus, we instead appeal to a helper predicate
that keeps track of which names are defined by which right-hand-sides
in a given module. (Observe that type tracking works correctly for `x`
in `mymodule.py`, even though `x` is never assigned a value in the
eyes of the Value API.)
This means that points-to is only used to actually figure out if the
object we're looking an attribute up on is a module or not. This is
the next thing to replace in order to eliminate the dependence on
points-to, but this will require some care to ensure that all module
lookups are handled correctly.
Only two test files needed to be changed for the tests to pass. The
first was the fixed false negative in the type tracker, and the other
was a bunch of missing flow in the regression test. I have manually
removed the `# Flow not found` annotations to make them consistent
with the output. Pay particular attention to the annotation on line
117 -- I believe it was misplaced and should have been on line 106
instead (where, indeed, we now have flow where none appeared before).
