[PATCH] D129531: [clang][C++20] P0960R3 and P1975R0: Allow initializing aggregates from a parenthesized list of values

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith added inline comments.


================
Comment at: clang/lib/Sema/SemaInit.cpp:6198-6199
+              dyn_cast<CXXRecordDecl>(DestType->getAs<RecordType>()->getDecl());
+          S.getLangOpts().CPlusPlus20 && RD && RD->isAggregate() && Failed() &&
+          getFailureKind() == FK_ConstructorOverloadFailed &&
+          onlyHasDefaultedCtors(getFailedCandidateSet())) {
----------------
For when you look at re-landing this, we encountered a regression for this case:

```
struct A {};
struct B : A { Noncopyable nc; };
```

Here, given `B b`, a `B(b)` direct-initialization should be rejected because it selects a deleted copy constructor of `B`, but it looks like Clang instead performed aggregate initialization, as if by `B{(const A&)b, {}}`. This is pretty bad -- copies that should be disallowed end up working but not actually copying any members of the derived class!

The general problem is that Clang's overload resolution incorrectly handles deleted functions, treating them as an overload resolution failure rather than a success. In this particular case, what happens is constructor overload resolution produces `OR_Deleted`, which gets mapped into `FK_ConstructorOverloadFailed` despite the fact that overload resolution succeeded and picked a viable function.

I guess we can split `FK_*OverloadFailed` into separate "failed" and "succeeded but found a deleted function" cases?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D129531/new/

https://reviews.llvm.org/D129531