Re: [PATCHv6] Handle TYPE_PACK_EXPANSION in cxx_incomplete_type_diagnostic

[Marek Polacek <polacek@redhat.com>]

On Mon, Jun 22, 2020 at 11:11:48PM -0400, Nicholas Krause wrote:
> 
> 
> On 6/22/20 10:01 PM, Marek Polacek wrote:
> > On Mon, Jun 22, 2020 at 09:42:51PM -0400, Nicholas Krause via Gcc-patches wrote:
> > > From: Nicholas Krause <xerofoify@gmail.com>
> > > 
> > > This fixs the PR95672 by adding the missing TYPE_PACK_EXPANSION case in
> > > cxx_incomplete_type_diagnostic in order to avoid ICES on diagnosing
> > > incomplete template pack expansion cases. In v2, add the missing required
> > > test case for all new patches. v3 Fixes both the test case to compile in
> > > C++11 mode and the message to print out only the type. v4 fixes the testcase
> > > to only target C++11. v5 and v6 fix the test case properly.
> > > 
> > > gcc/cp/ChangeLog:
> > > 
> > > 	* typeck2.c (cxx_incomplete_type_diagnostic): Add missing TYPE_EXPANSION_PACK
> > > 	  check for diagnosticing incomplete types in cxx_incomplete_type_diagnostic.
> > 
> > It's already been pointed out to you that it's "diagnosing".
> > 
> > > gcc/testsuite/ChangeLog:
> > > 
> > > 	* g++.dg/template/PR95672.C: New test.
> > > 
> > > Signed-off-by: Nicholas Krause <xerofoify@gmail.com>
> > > ---
> > >   gcc/cp/typeck2.c                        | 6 ++++++
> > >   gcc/testsuite/g++.dg/template/PR95672.C | 3 +++
> > >   2 files changed, 9 insertions(+)
> > >   create mode 100644 gcc/testsuite/g++.dg/template/PR95672.C
> > > 
> > > diff --git a/gcc/cp/typeck2.c b/gcc/cp/typeck2.c
> > > index 5fd3b82fa89..28b32fe0b5a 100644
> > > --- a/gcc/cp/typeck2.c
> > > +++ b/gcc/cp/typeck2.c
> > > @@ -552,6 +552,12 @@ cxx_incomplete_type_diagnostic (location_t loc, const_tree value,
> > >   		       TYPE_NAME (type));
> > >         break;
> > > +    case TYPE_PACK_EXPANSION:
> > > +     emit_diagnostic (diag_kind, loc, 0,
> > 
> > Bad indenting.
> 
> Sorry seems Jason didn't catch that.
> > 
> > > +		     "invalid use of pack expansion %qT",
> > > +		      type);
> > > +      break;
> > > +
> > >       case TYPENAME_TYPE:
> > >       case DECLTYPE_TYPE:
> > >         emit_diagnostic (diag_kind, loc, 0,
> > > diff --git a/gcc/testsuite/g++.dg/template/PR95672.C b/gcc/testsuite/g++.dg/template/PR95672.C
> > > new file mode 100644
> > > index 00000000000..fcc3da0a132
> > > --- /dev/null
> > > +++ b/gcc/testsuite/g++.dg/template/PR95672.C
> > > @@ -0,0 +1,3 @@
> > > +// PR c++/96572
> > > +// { dg-do compile}
> > > +// { dg-options "-std=c++11" }
> > > +struct g_class : decltype  (auto) ... {  }; // { dg-error "invalid use of pack expansion" }
> > 
> > No, this is completely broken.  It passes only because the patch file is
> > malformed and the last line will be lost when applying the patch, so the
> > test is an empty file.
> > 
> > Marek
> > 
> 
> Yes but now that I look at it seems the issue is that the error message was
> changed. My concern is that the test will have to be updated
> from the current every time the message changes like the current:
> error: expected primary-expression before ‘auto’
>     1 | struct g_class : decltype  (auto) ... {  };
> 
> Is this something I should care about as seems emit_diagnostic and friends
> sometimes do this.

decltype(auto) is a C++14 feature so won't work with -std=c++11.

Marek