C++: Split DataFlow::Node.asExpr into two predicates #774
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As we prepare to clarify how conversions are treated, we don't want a `sink(...)` declaration where it's non-obvious which conversions are applied to arguments.
With this change, the `IRDataflowTestCommon.qll` and `DataflowTestCommon.qll` files use the same definitions of sources and sinks. Since the IR data flow library is meant to be compatible with the AST data flow library, this is what we ought to be testing. Two alerts change but not necessarily for the right reasons.
The existing `Node.asExpr` predicate changes semantics so it becomes the one that most users should use when they don't want to think about `Conversion`s. A new `Node.asConvertedExpr` predicate is added and has the same semantics as the old `Node.asExpr` predicate. It's for advanced users that know about `Conversion`s and want to account for them.
dave-bartolomeo
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Jan 24, 2019
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OK, I think I agree that this is better than the status quo. I'm still uneasy about how this seems to blur the line between a reference and the referred-to object, but I think it's best to have that discussion once we've figured out what the new interface for pointer vs. pointee should be.
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This is my starting point for resolving https://jira.semmle.com/browse/CPP-318 (see also #597 (comment)). I expect we'll have to iterate for a few rounds to reach a compromise that satisfies all use cases, but I think this is better than the status quo.
In the 3rd commit I've implemented the most extreme of the proposals we've discussed on #597, yet it doesn't affect the test results. That means we need better test cases. Can you come up with a realistic test to show that this change leads to too much data flow?
I hope we agree on the following.
DataFlowshould not have to know or worry aboutConversions. They will set sources and sinks to unconverted expressions and expect the library to Do What They Mean.Conversions for sources and sinks.asExpr, which should err on the side of too much data flow.