[6.2] Fix argument index calculations for isolated default arguments #81377
+168
−5
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main
PR: #81370Explanation: The calculation of argument indices for isolated default arguments has a bug which is, fortunately, hidden by a second bug unless isolated default arguments are interleaved with other arguments, such as if an intermediate argument is provided explicitly by the call or meets the narrow conditions for being recognized as non-isolated.
Scope: affects the code path for all calls with isolated default arguments
Risk: Low: the survival of this bug until now suggests that existing code does not heavily exercise it
Testing: regression testing, new patch
Issue: rdar://150060837
Reviewer: Doug Gregor