Re: [PATCH] c++/78771 ICE with inheriting ctor

[Jason Merrill <jason at redhat dot com>]

On 12/19/2016 08:09 AM, Nathan Sidwell wrote:
> this patch fixes 78771, were an assert fires due to recursive
> instantiation of an inheriting ctor.  Normally when a recursive
> instantiation is needed, we've already constructed and registered the
> declaration, so simply return it.  For ctors though we need to construct
> the clones after we've instantiated the the master pattern (later in
> instantiate_template_1).  Hence any recursive instantiation of a cloned
> fn will barf, as we do.
>
> Now, with an inherited ctor we have to deduce its exception spec and
> deletedness (deduce_inheriting_ctor).  That's fine, until one gets the
> perverse testcase here.  In figuring out what Middle ctor is needed by
> Middle(0), we end up trying to instantiate Derived::Derived (int) to see
> if Middle::Middle (Derived) is a viable candidate.

Hmm, that seems like where the problem is.  We shouldn't try to 
instantiate the inheriting constructor until we've already chosen the 
base constructor; in the new model the inheriting constructor is just an 
implementation detail.

Jason