[PATCH] libstdc++: LWG 3301 transform_view::iterator has incorrect iterator_category

[Patrick Palka]

On Tue, 25 Feb 2020, Jonathan Wakely wrote:

> On 24/02/20 18:39 -0500, Patrick Palka wrote:
> > On Mon, 24 Feb 2020, Patrick Palka wrote:
> > 
> > > libstdc++-v3/ChangeLog:
> > > 
> > > 	LWG 3301 transform_view::_Iterator has incorrect iterator_category
> > > 	* include/std/ranges (transform_view::_Iterator::_S_iter_cat): Adjust
> > > 	determination of iterator_category as per LWG 3301.
> > > 	* testsuite/std/ranges/adaptors/transform.cc: Augment test.
> > > ---
> > >  libstdc++-v3/include/std/ranges               | 16 +++++++++----
> > >  .../std/ranges/adaptors/transform.cc          | 24 +++++++++++++++++++
> > >  2 files changed, 35 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/libstdc++-v3/include/std/ranges
> > > b/libstdc++-v3/include/std/ranges
> > > index ab8fbaca38f..aed90e9710e 100644
> > > --- a/libstdc++-v3/include/std/ranges
> > > +++ b/libstdc++-v3/include/std/ranges
> > > @@ -1570,12 +1570,18 @@ namespace views
> > >  	  static constexpr auto
> > >  	  _S_iter_cat()
> > >  	  {
> > > -	    using _Cat
> > > -              = typename iterator_traits<_Base_iter>::iterator_category;
> > > -	    if constexpr (derived_from<_Cat, contiguous_iterator_tag>)
> > > -	      return random_access_iterator_tag{};
> > > +	    using _Res = invoke_result_t<_Fp&, range_reference_t<_Base>>;
> > 
> > Consider this line fixed to use 'typename'.
> > 
> > > +	    if constexpr (is_lvalue_reference_v<_Res>)
> > > +	      {
> > > +		using _Cat
> > > +		  = typename iterator_traits<_Base_iter>::iterator_category;
> > > +		if constexpr (derived_from<_Cat, contiguous_iterator_tag>)
> > > +		  return random_access_iterator_tag{};
> > > +		else
> > > +		  return _Cat{};
> > > +	      }
> > >  	    else
> > > -	      return _Cat{};
> > > +	      return input_iterator_tag{};
> > >  	  }
> > > 
> > >  	  static constexpr decltype(auto)
> > > diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/transform.cc
> > > b/libstdc++-v3/testsuite/std/ranges/adaptors/transform.cc
> > > index ad51fffb43d..0845febe2cf 100644
> > > --- a/libstdc++-v3/testsuite/std/ranges/adaptors/transform.cc
> > > +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/transform.cc
> > > @@ -77,10 +77,34 @@ test03()
> > >    VERIFY( ranges::equal(v, (int[]){1,2,3,4,5}) );
> > >  }
> > > 
> > > +void
> > > +test04()
> > > +{
> > > +  // LWG 3302
> > 
> > Consider this comment fixed to say 3301.
> 
> OK, thanks.

Thanks for the review, I just committed all five patches.