C++: replace ReturnValue nodes in flow paths

[rdmarsh2]

Improves data flow path readability for C++ by hiding the per-function ReturnValue nodes and forcing the nodes created for each ReturnStmt to be included in the displayed path. This also adds a new nodeIsShown predicate to the data flow library's per-language interface.

[rdmarsh2]

Opened as draft so I can do performance evaluations and get input from the data flow library maintainers.

[MathiasVP]

We could hack this without changing the shared library by repurposing the CastNode class. However, I do like having a Please show this node in the final path feature that's more explicit than just marking everything as cast nodes when debugging paths 👍.

[aschackmull]

Ah, right, yeah I see the problem you're trying to solve. I think we ought to solve this entirely within the shared library without the need for a new interface predicate.

[aschackmull]

Do you envision other use-cases for a "Please show this node in the final path"-feature? Because I'm leaning towards considering the specific short-coming around synthesised return nodes as a bug in the shared library, which can be fixed without such a feature.

[MathiasVP]

Do you envision other use-cases for a "Please show this node in the final path"-feature? Because I'm leaning towards considering the specific short-coming around synthesised return nodes as a bug in the shared library, which can be fixed without such a feature.

The return node use-case is the only one I've encountered so far, at least. Can you think of other use-cases @rdmarsh2?

[rdmarsh2]

I didn't envision any other use-cases. If you can make a shared library fix for it, that's better than adding a new predicate to the interface.