[Bug c++/71217] New: [concepts] Incorrect recursive concept evaluation

[sergstrukovlink at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71217

Bug ID: 71217
   Summary: [concepts]  Incorrect recursive concept evaluation
   Product: gcc
   Version: 6.1.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: sergstrukovlink at gmail dot com
  Target Milestone: ---

Created attachment 38538
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38538&action=edit
the sample program

The attached file contains a sample program to show the problem.

/* struct Fold */

template  struct Fold;

/* concept TestInt */

template 
struct IntFoldCtor
 {
  enum RetType { Ret = false };
 };

template 
concept bool TestInt = (bool)IntFoldCtor::Ret || is_same::value ;

template 
struct IntFoldCtor >
 {
  enum RetType { Ret = true };
 };

TestInt< Fold,int> > is evaluated (incorrectly) as false.

Here is a link to forum discussion of the problem

https://groups.google.com/a/isocpp.org/forum/#!topic/concepts/k-PFfgLloXI

[Bug c++/71223] New: [fold expression] Incorrect processing a fold expression

[sergstrukovlink at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71223

Bug ID: 71223
   Summary: [fold expression] Incorrect processing a fold
expression
   Product: gcc
   Version: 6.1.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: sergstrukovlink at gmail dot com
  Target Milestone: ---

Created attachment 38539
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38539&action=edit
example

In the attached example compiler fails to compile the following line

  Test2(); // emits error

If I change the definition of

template 
using AddType = TypeBox ; // int 

to

template 
using AddType = int ;

the error disappeares.

main.cpp: In instantiation of 'struct Test2':
main.cpp:41:25:   required from here
main.cpp:23:74: error: invalid use of pack expansion expression
 using IndexList = decltype( ( IndexListBox<>() + ... + AddType() ) ) ;
  ^
make: *** [main.o] Error 1