PATCH RFC: Proposed patch for PR c++/7874

[Mark Mitchell]

Ian Lance Taylor wrote:

> Now that my patch handles the above case correctly, the test
> g++.dg/template/friend10.C fails.  And the original test case in PR
> 5116 fails.
>
> I think the issue here is whether we should prefer an explicitly
> declared conversion operator over a friend function found using
> argument dependent lookup.  With my current patch, we prefer the
> conversion operator.  (When friends are injected, we prefer the friend
> function, which seems straightforward and correct.)
> 
> Can somebody with more C++-fu than I have take a look at these two
> cases and see what is correct?  Thanks.

Let's start with the simpler friend10.C.  There, the "operator bool()"
conversion operator is irrelevant, as far as I can see.  However, we
*should* still call the friend operator<<, because argument-dependent
lookup is explicitly defined that way.

So, in that particular form of lookup, you should ignore
DECL_ANTICIPATED -- but only if the friend was declared in one of the
classes that's in the set of special classes.  I guess, without changing
our representation, you get to go through each of the DECL_ANTICIPATED
friends, and then call is_friend (fn, c) for each c in the set of
argument-dependent classes.  That's wort-case quadratic, and we could
make it cleverer, but I'd start with that.

-- 
Mark Mitchell
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