Previously, in cases like
```python
def foo(x):
x.bar()
x.baz()
x.quux()
```
we would have flow from the first `x` to each use _and_ flow from the
post-update node for each method call to each subsequent use, and all
of these would be `LocalSourceNode`s. For large functions with the above
pattern, this would lead to a quadratic blowup in `hasLocalSource`.
With this commit, only the first of these will count as a
`LocalSourceNode`, and the blowup disappears.
The meat of this PR is described in the new python/ql/test/experimental/meta/InlineTaintTest.qll file:
> Defines a InlineExpectationsTest for checking whether any arguments in
> `ensure_tainted` and `ensure_not_tainted` calls are tainted.
>
> Also defines query predicates to ensure that:
> - if any arguments to `ensure_not_tainted` are tainted, their annotation is marked with `SPURIOUS`.
> - if any arguments to `ensure_tainted` are not tainted, their annotation is marked with `MISSING`.
>
> The functionality of this module is tested in `ql/test/experimental/meta/inline-taint-test-demo`.
In some cases, we were joining the result of `val.getClass()` against
the first argument of `Types::improperSubclass` before filtering out the
vast majority of tuples by the call to `isinstance_call`.
To fix this, we let `isinstance_call` take care of figuring out the
class of the value being tested. As a bonus, this cleans up the only
other place where `isinstance_call` is used, where we _also_ want to
know the class of the value being tested in the `isinstance` call.
The recent change to `appliesTo` lead to a perturbation in the join
order of this predicate, which resulted in a cartesian product between
`call` and `ctx` being created (before being filtered by `appliesTo`).
By splitting the intermediate result into its own helper predicate,
suitably marked to prevent inlining/magic, we prevent this from
happening again.
The `CallCfgNode` restrictions are familiar and useful.
Restricting `InstanceSource` to extend `LocalSourceNode` is novel, but I
think it makes sense. It will act as a good reminder to anyone extending
`InstanceSource` that the node in question is a `LocalSourceNode`, which
will be enforced by the return type of the internal type tracker anyway.
I wasn't able to roll out API graphs as widely in Tornado as I had
hoped, since we're lacking the "def" part. This means most of the
`InstanceSource` machinery will have to stay.
