... in a local scope. Or rather, remove these from the `hasLocalSource`
relation.
This prevents a quadratic blowup when the same global is mentioned
_a lot_ of times within a single function scope.
Temporarily instates `TypeTrackingNode` as an alias of `LocalSourceNode`
as having it as a separate class lead to performance regressions.
In the hopes that this will be resolved in the near future, I have left
the current `TypeTrackingNode` implementation in situ, but hidden inside
a `FutureWork` private module.
Not the prettiest of solutions, but it does the job. Basically, we were
calculating (and re-calculating) the same big relation between strings
and regexes and then checking whether the latter matched the former.
This resulted in tuple counts like the following:
```
[2021-07-12 16:09:24] (12s) Tuple counts for SensitiveDataSources::SensitiveDataModeling::SensitiveVariableAssignment#class#ff#shared/4@7489c6:
4918074 ~0% {4} r1 = JOIN SensitiveDataHeuristics::HeuristicNames::maybeSensitiveRegexp#ff WITH Flow::NameNode::getId_dispred#ff CARTESIAN PRODUCT OUTPUT Lhs.0 'arg0', Lhs.1 'arg1', Rhs.0, Rhs.1 'arg3'
2654 ~0% {4} r2 = JOIN r1 WITH PRIMITIVE regexpMatch#bb ON Lhs.3 'arg3',Lhs.1 'arg1'
return r2
```
(The above being just the bit that handles `DefinitionNode` in
`SensitiveVariableAssignment`, and taking 12 seconds to evaluate.)
By applying a bit of manual inlining and magic, this becomes somewhat
more manageable:
```
[2021-07-12 15:59:44] (1s) Tuple counts for SensitiveDataSources::SensitiveDataModeling::sensitiveString#ff/2@8830e2:
27671 ~2% {3} r1 = JOIN SensitiveDataHeuristics::HeuristicNames::maybeSensitiveRegexp#ff WITH SensitiveDataSources::SensitiveDataModeling::sensitiveParameterName#f CARTESIAN PRODUCT OUTPUT Lhs.0 'classification', Lhs.1, Rhs.0
334012 ~2% {3} r2 = JOIN SensitiveDataHeuristics::HeuristicNames::maybeSensitiveRegexp#ff WITH SensitiveDataSources::SensitiveDataModeling::sensitiveName#f CARTESIAN PRODUCT OUTPUT Lhs.0 'classification', Lhs.1, Rhs.0
361683 ~11% {3} r3 = r1 UNION r2
154644 ~0% {3} r4 = JOIN SensitiveDataHeuristics::HeuristicNames::maybeSensitiveRegexp#ff WITH SensitiveDataSources::SensitiveDataModeling::sensitiveFunctionName#f CARTESIAN PRODUCT OUTPUT Lhs.0 'classification', Lhs.1, Rhs.0
149198 ~1% {3} r5 = JOIN SensitiveDataHeuristics::HeuristicNames::maybeSensitiveRegexp#ff WITH SensitiveDataSources::SensitiveDataModeling::sensitiveStrConst#f CARTESIAN PRODUCT OUTPUT Lhs.0 'classification', Lhs.1, Rhs.0
124257 ~5% {3} r6 = JOIN SensitiveDataHeuristics::HeuristicNames::maybeSensitiveRegexp#ff WITH SensitiveDataSources::SensitiveDataModeling::sensitiveAttributeName#f CARTESIAN PRODUCT OUTPUT Lhs.0 'classification', Lhs.1, Rhs.0
273455 ~21% {3} r7 = r5 UNION r6
428099 ~30% {3} r8 = r4 UNION r7
789782 ~78% {3} r9 = r3 UNION r8
1121 ~77% {3} r10 = JOIN r9 WITH PRIMITIVE regexpMatch#bb ON Lhs.2 'result',Lhs.1
1121 ~70% {2} r11 = SCAN r10 OUTPUT In.0 'classification', In.2 'result'
return r11
```
(The above being the total for all the sensitive names we care about,
taking only 1.2 seconds to evaluate.)
Incidentally, you may wonder why this has _fewer_ results than before.
The answer is control flow splitting -- every sensitively-named
`DefinitionNode` would have been matched in isolation previously. By
pre-matching on just the names of these, we can subsequently join
against those names that are known to be sensitive, which is a much
faster operation.
(We also get the benefit of deduplicating the strings that are matched,
before actually performing the match, so if, say, an attribute name and
a variable name are identical, then we'll only match them once.)
We also exclude all docstrings as relevant string constants, as these
presumably don't actually flow anywhere.
Splits `ModuleVariableNode` away from `LocalSourceNode`, instead
creating a class `TypeTrackingNode` that encapsulates both of these.
This means we no longer have module variable nodes as part of
`LocalSourceNode` (which is good, since they have no "local" aspect to
them), and hence we can have `LocalSourceNode` inherit directly from
`ExprNode` (which makes the API a bit nicer).
Unfortunately these are breaking changes, so we can't actually fulfil
the above two desiderata until the `track` and `backtrack` methods on
`LocalSourceNode` have been fully deprecated. For this reason, we
preserve the present implementation of `LocalSourceNode`, and instead
lay the foundation for switching over in the future, by deprecating
`track` and `backtrack` on `LocalSourceNode`.
