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…here are no arguments to forward.
…ersions. For now we don't implement any converions other than array-to-pointer, but we will add conversions in a later commit.
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Copilot review overview
🟡 Changes recommended
Zero-argument forwarding currently cannot select a zero-parameter constructor.
Review effort: Balanced
Findings: 1
Open (2)
What changed in this PR
Improves constructor selection for C++ perfect-forwarding models using conversion-aware type matching.
Changes:
- Models standard and user-defined conversions, value categories, and reference binding.
- Integrates constructor selection into synthetic data-flow nodes.
- Adds comprehensive forwarding tests and updates existing expectations.
| File | Description |
|---|---|
forwarding/test.ql |
Tests selected constructors. |
forwarding/test.ext.yml |
Defines the test forwarding model. |
forwarding/test.expected |
Records test expectations. |
forwarding/test.cpp |
Covers C++ conversion scenarios. |
external-models/test.cpp |
Updates known forwarding false positives. |
external-models/flow.expected |
Updates generated flow expectations. |
DataFlowPrivate.qll |
Delegates constructor selection. |
DataFlowNodes.qll |
Connects forwarding nodes to the new logic. |
ExternalFlow.qll |
Implements conversion-aware constructor matching. |
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In #22532 we added support for specifying whether a modelled function forward all its arguments. However, we implemented very some naive logic for identifying the constructor to invoke when given a type and a set of argument types. This PR fixes that by modelling (to the best of my abilities) the conversion rules and type matching of C++ to correctly map a list of arguments to a constructor.
We use a flow-based approach where we check if a sequence of steps can flow from a "source" (an argument type) to a "sink" (a constructor parameter type) using 0 or more steps (type conversions).
Unsurprisingly, C++ rules make this rather complicated. There are a few missing results still (related to how CV qualifiers are being treated), and spurious results (related to how overload resolution ranks conversions) but I'd prefer to leave those for as future work.
There are many commits since I worked tirelessly to ensure that each commit can be reviewed in isolation. Please thank me by reviewing it commit-by-commit! 😅
DCA is uneventful since we don't yet use this feature in any non-test models. However, I've got a PR coming up that makes heavy use of this where this makes a real difference.