A slightly odd fix, but still morally okay, I think. The main issue
here was that global variables have their first occurrence in an inner
scope inside a so-called "scope entry definition", that then
subsequently flows to the first use of this variable. This meant that
that first use was _not_ a `LocalSourceNode` (since _something_ flowed
into it), and this blocked `trackUseNode` from type-tracking to it (as
it expects all nodes to be `LocalSourceNode`s).
The answer, then, is to say that a `LocalSourceNode` is simply one
that doesn't have flow to it from _any `CfgNode`_ (through one or more
steps). This disregards the flow from the scope entry definition, as
that is flow from an `EssaNode`.
Additionally, it makes sense to exclude `ModuleVariableNode`s. These
should never be considered local sources, since they always have flow
from (at least) the place where the corresponding global variable is
introduced.
This turned out to be fairly simple. Given an import such as
```python
from foo.bar.baz import quux
```
we create an API-graph node for each valid dotted prefix of
`foo.bar.baz`, i.e. `foo`, `foo.bar`, and `foo.bar.baz`. For these, we
then insert nodes in the API graph, such that `foo` steps to `foo.bar`
along an edge labeled `bar`, etc.
Finally, we only allow undotted names to hang off of the API-graph
root. Thus, `foo` will have a `moduleImport` edge off of the root, and
a `getMember` edge for `bar` (which in turn has a `getMember` edge for
`baz`).
Relative imports are explicitly ignored.
Finally, this commit also adds inline tests for a variety of ways of
importing modules, including a copy of the "import-helper" tests (with
a few modifications to allow a single annotation per line, as these
get rather long quickly!).
Currently only supports the "use" side of things.
For the most part, this follows the corresponding implementation for
JavaScript. Major differences include:
- No `MkImportUse` nodes -- we just move directly from
`MkModuleImport` to its uses.
- Paths are no longer labelled by s-expressions, but rather by a
string that mirrors how you would access it in QL. This makes it very
easy to see how to access an API component -- simply look at its
`toString`!
This PR also extends `LocalSourceNode` to support looking up attribute
references and invocations of such nodes. This was again based on the
JavaScript equivalent (though without specific classes for
`InvokeNode` and the like, it's a bit more awkward to use).
- align synthetic pre-update nodes with synthetic post -update nodes
- move the classes into the modules
- rename modules after the new main class (eliding "needs")
