[cfe-dev] C++ friend Constructor with Templates

[John McCall via cfe-dev]

> On Aug 6, 2018, at 12:44 PM, Matt Miller via cfe-dev <cfe-dev at lists.llvm.org> wrote:
> 
> I was wondering if the following clang behavior is expected/standard compliant:
> 
> 1. non-template friend function (not constructor): compiles in gcc and clang
> 2. non-template friend constructor: compiles in gcc and clang
> 3. template friend function (not constructor): compiles in gcc and clang
> 4. template friend constructor: compiles in gcc , but not clang
> (compiled in clang 3.0.0 but not clang 3.1+)
> 
> Here is an example (use -DUSE_TEMPLATE to control whether the template
> or non-template code is compiled):
> 
> https://godbolt.org/g/FT7Mzj
> 
> In the clang case for (4), it gives an error as if the friend
> declaration was never made.
> 
> Looking at a C++ standard:
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/n4659.pdf
> 
> It looks like section 14.3.5 gives an explicit example of a
> non-template friend constructor being allowed.  In 17.5.4, it didn't
> look like there was anything to indicate template friend constructors
> are treated different than template friend non-constructor functions,
> but maybe I'm missing a subtle point in that section or elsewhere.

No, it looks like a bug to me.  Would you mind filing it?
  https://bugs.llvm.org <https://bugs.llvm.org/>

John.
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