[cfe-dev] interesting c++ puzzle

[Richard Smith]

Neither 5.cpp nor 6.cpp have the problematic pattern.

The issue is that (for the case in PR8539 comment#2), when trying to
construct a B from a B temporary, we can't use the B(B&) constructor
and try the B(const A&) constructor. That tries to copy-initialize an
A temporary from the B temporary, which looks at A's constructors and
selects the A(B) constructor.

Then overload resolution terminates and we perform the initialization,
and that tries to construct a B from a B temporary. And around we go.
It should be straightforward to detect this and reject this after
constructing an InitializationSequence; if the first step is a
SK_ConstructorInitialization which performs the same conversion as the
overall sequence, then we have an error.

On Wed, Jan 16, 2013 at 1:04 PM, reed kotler <rkotler at mips.com> wrote:
> I'm far from a c++ language lawyer. I decided, in my spare time,  to work on
> some involved language related clang bugs to reverse that situation.
>
> I picked this one http://llvm.org/bugs/show_bug.cgi?id=8539 .
>
> I've been trying to understand the rules surrounding this bug, which
> interestingly enough used to cause g++ to crash and still causes clang as
> well as the sun compiler to crash.
>
> Here is an interesting pair of test cases I came up with.
>
> 5.cpp gets the same result on at least 4 compilers. It compiles correctly,
> and prints B(1)
>
> 6.cpp does not compile on clang++ or g++.
>
> This seems illogical to me. It does not call the copy constructor in 5.cpp
> but in 6.cpp it tails
> to compile because it can't find a valid copy constructor.
>
> I have a number of other related test cases. I want to make a fix that
> really fixes this general class of issues and not just make the crash go
> away for that one test case.
>
> On other compilers, both 5.cpp and 6.cpp get the same result.
>
> Tia.
>
> Reed
>
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