[Bug c++/91364] Implement P0388R4: Permit conversions to arrays of unknown bound

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91364

Marek Polacek  changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
   Last reconfirmed||2019-08-05
 Ever confirmed|0   |1

[Bug c++/91364] Implement P0388R4: Permit conversions to arrays of unknown bound

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91364

--- Comment #1 from Marek Polacek  ---
Sort of depends on CWG 2352 Similar types and reference binding which changed
the definition of "reference-related".

[Bug c++/91364] Implement P0388R4: Permit conversions to arrays of unknown bound

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91364
Bug 91364 depends on bug 91844, which changed state.

Bug 91844 Summary: Implement CWG 2352, Similar types and reference binding
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91844

   What|Removed |Added

 Status|ASSIGNED|RESOLVED
 Resolution|--- |FIXED

[Bug c++/91364] Implement P0388R4: Permit conversions to arrays of unknown bound

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91364

Marek Polacek  changed:

   What|Removed |Added

 Status|NEW |ASSIGNED
   Assignee|unassigned at gcc dot gnu.org  |mpolacek at gcc dot 
gnu.org

--- Comment #2 from Marek Polacek  ---
Workin' on it.

[Bug c++/91364] Implement P0388R4: Permit conversions to arrays of unknown bound

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91364

Marek Polacek  changed:

   What|Removed |Added

   Keywords||patch

--- Comment #3 from Marek Polacek  ---
https://gcc.gnu.org/ml/gcc-patches/2019-10/msg00395.html

[Bug c++/91364] Implement P0388R4: Permit conversions to arrays of unknown bound

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91364

--- Comment #4 from Marek Polacek  ---
Note to myself: while messing with this, perhaps implement DR 330 too for good
measure.  Bug 88128.

[Bug c++/91364] Implement P0388R4: Permit conversions to arrays of unknown bound

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91364

--- Comment #5 from Marek Polacek  ---
Author: mpolacek
Date: Wed Oct  9 20:58:00 2019
New Revision: 276771

URL: https://gcc.gnu.org/viewcvs?rev=276771&root=gcc&view=rev
Log:
Implement C++20 P0388R4, DR 1307, and DR 330.

This patch implements P0388R4, Permit conversions to arrays of unknown bound,
.  CWG 393 allowed references to arrays of unknown
bound and this C++20 feature allows conversions like

  void f(int(&)[]);
  int arr[1];

  void g() { f(arr); }
  int(&r)[] = arr;

The proposal seemed fairly straightforward but it turned out to be quite
shifty.  I found out that I needed to implement DR 2352 (done), and also
DR 1307 (done in this patch).  The latter DR added wording for
list-initialization ranking of references to arrays which this proposal
extends.  DR 330 was also implemented in this patch.

PR c++/91364 - P0388R4: Permit conversions to arrays of unknown bound.
PR c++/69531 - DR 1307: Differently bounded array parameters.
PR c++/88128 - DR 330: Qual convs and pointers to arrays of pointers.
* call.c (build_array_conv): Build ck_identity at the beginning
of the conversion.
(standard_conversion): Pass bounds_none to comp_ptr_ttypes_const.
(maybe_warn_array_conv): New.
(convert_like_real): Call it.  Add an error message about converting
from arrays of unknown bounds.
(conv_get_original_expr): New.
(nelts_initialized_by_list_init): New.
(conv_binds_to_array_of_unknown_bound): New.
(compare_ics): Implement list-initialization ranking based on
array sizes, as specified in DR 1307 and P0388R.
* cp-tree.h (comp_ptr_ttypes_const): Adjust declaration.
(compare_bounds_t): New enum.
* typeck.c (comp_array_types): New bool and compare_bounds_t
parameters.  Use them.
(structural_comptypes): Adjust the call to comp_array_types.
(similar_type_p): Handle ARRAY_TYPE.
(build_const_cast_1): Pass bounds_none to comp_ptr_ttypes_const.
(comp_ptr_ttypes_real): Don't check cv-quals of ARRAY_TYPEs.  Use
comp_array_types to compare array types.  Look through arrays as per
DR 330.
(comp_ptr_ttypes_const): Use comp_array_types to compare array types.
Look through arrays as per DR 330.

* g++.dg/conversion/qual1.C: New test.
* g++.dg/conversion/qual2.C: New test.
* g++.dg/conversion/qual3.C: New test.
* g++.dg/conversion/ref2.C: New test.
* g++.dg/conversion/ref3.C: New test.
* g++.dg/cpp0x/initlist-array3.C: Remove dg-error.
* g++.dg/cpp0x/initlist-array7.C: New test.
* g++.dg/cpp0x/initlist-array8.C: New test.
* g++.dg/cpp2a/array-conv1.C: New test.
* g++.dg/cpp2a/array-conv10.C: New test.
* g++.dg/cpp2a/array-conv11.C: New test.
* g++.dg/cpp2a/array-conv12.C: New test.
* g++.dg/cpp2a/array-conv13.C: New test.
* g++.dg/cpp2a/array-conv14.C: New test.
* g++.dg/cpp2a/array-conv15.C: New test.
* g++.dg/cpp2a/array-conv16.C: New test.
* g++.dg/cpp2a/array-conv17.C: New test.
* g++.dg/cpp2a/array-conv2.C: New test.
* g++.dg/cpp2a/array-conv3.C: New test.
* g++.dg/cpp2a/array-conv4.C: New test.
* g++.dg/cpp2a/array-conv5.C: New test.
* g++.dg/cpp2a/array-conv6.C: New test.
* g++.dg/cpp2a/array-conv7.C: New test.
* g++.dg/cpp2a/array-conv8.C: New test.
* g++.dg/cpp2a/array-conv9.C: New test.
* g++.old-deja/g++.bugs/900321_01.C: Adjust dg-error.

* testsuite/23_containers/span/lwg3255.cc: Adjust test to match the
post-P0388R4 behavior.


Added:
trunk/gcc/testsuite/g++.dg/conversion/qual1.C
trunk/gcc/testsuite/g++.dg/conversion/qual2.C
trunk/gcc/testsuite/g++.dg/conversion/qual3.C
trunk/gcc/testsuite/g++.dg/conversion/ref2.C
trunk/gcc/testsuite/g++.dg/conversion/ref3.C
trunk/gcc/testsuite/g++.dg/cpp0x/initlist-array7.C
trunk/gcc/testsuite/g++.dg/cpp0x/initlist-array8.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv1.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv10.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv11.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv12.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv13.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv14.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv15.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv16.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv17.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv2.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv3.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv4.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv5.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv6.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv7.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv8.C
trunk/gcc/testsuit

[Bug c++/91364] Implement P0388R4: Permit conversions to arrays of unknown bound

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91364
Bug 91364 depends on bug 69531, which changed state.

Bug 69531 Summary: Implement CWG 1307; Differently bounded array parameters
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69531

   What|Removed |Added

 Status|ASSIGNED|RESOLVED
 Resolution|--- |FIXED

[Bug c++/91364] Implement P0388R4: Permit conversions to arrays of unknown bound

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91364
Bug 91364 depends on bug 88128, which changed state.

Bug 88128 Summary: G++ should implement CWG 330
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88128

   What|Removed |Added

 Status|ASSIGNED|RESOLVED
 Resolution|--- |FIXED

[Bug c++/91364] Implement P0388R4: Permit conversions to arrays of unknown bound

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91364

Marek Polacek  changed:

   What|Removed |Added

 Status|ASSIGNED|RESOLVED
 Resolution|--- |FIXED

--- Comment #6 from Marek Polacek  ---
Implemented for GCC 10.

[Bug c++/91364] Implement P0388R4: Permit conversions to arrays of unknown bound

[wjwray at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91364

Will Wray  changed:

   What|Removed |Added

 CC||wjwray at gmail dot com

--- Comment #7 from Will Wray  ---
Fails to match for variadic arguments. Reopen or file a new bug?

https://godbolt.org/z/zuJagw

#include 

void cat(auto const(&...a)[]);
//void cat(auto const(&...)[]); // REJECT error: variable or field
//  'cat' declared void
void cat(auto const(&)[]...);   // ACCEPT: is this well formed? (IDK)
void cat(auto const(&a)[]...);  // ACCEPT: is this well formed? (IDK)
//can't provide a definition

// If the char[6] overload below is removed then this [] overload fails:
//   error: no matching function for call to 'cat(const char [6]...)'
void cat(auto const(&...cstr)[]) { (puts(cstr),...); }

void cat(auto const(&...cstr)[6]) { (puts(cstr),...); }

int main() {
cat("Hello","world");
}

[Bug c++/91364] Implement P0388R4: Permit conversions to arrays of unknown bound

[wjwray at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91364

--- Comment #8 from Will Wray  ---
Reduced example (but still with puts output) https://godbolt.org/z/Ttc2Za

#include 
void cat(auto const(&...cstr)[]) { (puts(cstr),...); }
// Comment out this next line[6]
void cat(auto const(&...cstr)[6]) { (puts(cstr),...); }

int main() { cat("Hello","world"); }

Fails to match the 1st overload when the 2nd overload is removed

Answering my own question "is this well formed?"

void cat(auto const(&a)[]...);

Yes; it matches T(&)[] type argument exactly https://godbolt.org/z/NHjPrK

[Bug c++/91364] Implement P0388R4: Permit conversions to arrays of unknown bound

[wjwray at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91364

--- Comment #9 from Will Wray  ---
The variadic unknown-bound 1st overload matches exact T(&)[] only
https://godbolt.org/z/9qZpWX

#include 
void cat(auto const(&...cstr)[]) { (((void)cstr,puts("G'bye")),...); }
void cat(auto const(&...cstr)[6]) { (puts(cstr),...); }

using punk = char(*)[]; // Pointer to UNKnown-bound char array

int main() {
cat("Hello");  // Outputs "Hello" via 2nd overload
cat(*punk{});  // Outputs "G'bye" via 1st overload
}

[Bug c++/91364] Implement P0388R4: Permit conversions to arrays of unknown bound

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91364

--- Comment #10 from Marek Polacek  ---
(In reply to Will Wray from comment #7)
> Fails to match for variadic arguments. Reopen or file a new bug?

Definitely a new bug, please.