[Bug c++/97234] Constexpr class-scope array initializer referencing previous elements

[botond at mozilla dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97234

Botond Ballo  changed:

   What|Removed |Added

   See Also||https://gcc.gnu.org/bugzill
   ||a/show_bug.cgi?id=99059

--- Comment #3 from Botond Ballo  ---
Bug 99059 is similar (involving C++17 "inline" rather than constexpr) and
Jonathan Wakely said it's a bug.

[Bug c++/97234] Constexpr class-scope array initializer referencing previous elements

[botond at mozilla dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97234

--- Comment #2 from Botond Ballo  ---
I believe it's valid because the point of declaration of a variable is just
before its initializer
(https://timsong-cpp.github.io/cppwp/n4861/basic.scope.pdecl#1), and thus the
variable should be in scope in its initializer.

But I'm not a wording expert and it's possible I'm mistaken, or overlooking
something else that would make this invalid.

[Bug c++/100644] New: [11 regression] Deleted move constructor prevents templated constructor from being used

[botond at mozilla dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100644

Bug ID: 100644
   Summary: [11 regression] Deleted move constructor prevents
templated constructor from being used
   Product: gcc
   Version: 11.1.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: botond at mozilla dot com
  Target Milestone: ---

GCC 11 gives an error for the following code which GCC 10 and Clang accept:


struct NonMovable {
  NonMovable(NonMovable&&) = delete;
};

template 
struct Maybe {
  NonMovable mMember;

  template 
  Maybe(Maybe&&);
};

void foo(Maybe);

void unlucky(Maybe&& x) {
  Maybe var{(Maybe&&)x};
}


The error is:


main.cpp: In function ‘void unlucky(Maybe&&)’:
main.cpp:16:33: error: use of deleted function
‘Maybe::Maybe(Maybe&&)’
   16 |   Maybe var{(Maybe&&)x};
  | ^
main.cpp:6:8: note: ‘Maybe::Maybe(Maybe&&)’ is implicitly deleted
because the default definition would be ill-formed:
6 | struct Maybe {
  |^
main.cpp:6:8: error: use of deleted function
‘NonMovable::NonMovable(NonMovable&&)’
main.cpp:2:3: note: declared here
2 |   NonMovable(NonMovable &&) = delete;
  |   ^~


I believe the code should be accepted, with the deleted move constructor
ignored during overload resolution and the templated constructor used instead.

I explain my reasoning, with links to the standard, in more detail here:
https://bugzilla.mozilla.org/show_bug.cgi?id=1710235#c22

Please let me know if I've overlooked something and the code really is invalid.

[Bug c++/97234] New: Constexpr class-scope array initializer referencing previous elements

[botond at mozilla dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97234

Bug ID: 97234
   Summary: Constexpr class-scope array initializer referencing
previous elements
   Product: gcc
   Version: 10.1.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: botond at mozilla dot com
  Target Milestone: ---

The following code:

struct S {
static constexpr int rolling_sum[4]{
0,
rolling_sum[0] + 1,
rolling_sum[1] + 2,
rolling_sum[2] + 3
};
};

produces errors when compiled with g++ 10:

test.cpp:4:9: error: ‘rolling_sum’ was not declared in this scope
4 | rolling_sum[0] + 1,
  | ^~~
test.cpp:5:9: error: ‘rolling_sum’ was not declared in this scope
5 | rolling_sum[1] + 2,
  | ^~~
test.cpp:6:9: error: ‘rolling_sum’ was not declared in this scope
6 | rolling_sum[2] + 3
  |   

The code is accepted by clang. It's also accepted by gcc if the array is
declared at namespace scope, leading me to believe that rejecting it at class
scope is likely a bug.