[Bug c++/49015] New: [C++0x] Non-defining constexpr function declarations require complete argument/return types

[Bug c++/49015] New: [C++0x] Non-defining constexpr function declarations require complete argument/return types

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49015

           Summary: [C++0x] Non-defining constexpr function declarations
                    require complete argument/return types
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: daniel.kruegler@googlemail.com
                CC: jason@redhat.com


After successful resolution of bug 48948 gcc 4.7.0 20110514 (experimental) in
C++0x mode now rejects the following code at the lines marked with #L-4 until
#L-13:

//---
class A;
class B;

constexpr B f(A); // #L-4

class B {
  friend constexpr B g(A); // #L-7
};

class A {};

constexpr B f(A) { return B(); } // #L-12
constexpr B g(A) { return B(); } // #L-13
//---

"4|error: invalid type for parameter 1 of constexpr function 'constexpr B
f(A)'|
4|error: invalid return type 'B' of constexpr function 'constexpr B f(A)'|
7|error: invalid type for parameter 1 of constexpr function 'constexpr B g(A)'|
7|error: invalid type for parameter 1 of constexpr function 'constexpr B g(A)'|
|In function 'constexpr B f(A)':|
12|error: redeclaration 'constexpr B f(A)' differs in 'constexpr'|
4|error: from previous declaration 'B f(A)'|
|In function 'constexpr B g(A)':|
13|error: redeclaration 'constexpr B g(A)' differs in 'constexpr'|
7|error: from previous declaration 'B g(A)'|
||=== Build finished: 8 errors, 0 warnings ===|

The parts following line 8 have mainly be added to demonstrate the general
usefulness of the non-defining declarations and the error described by #L-12
and #L-13 is possibly overlaid by bug 48945 as well, so the main aspect of this
issue are the #L-4 and #L-7 rejections if interaction with bug 48945 is the
cause of #L-12 and #L-13.

I don't think that the literal-type requirements as of 3.9 p. 10 impose the
requirements of complete types for the non-defining declarations of these
constexpr functions, IMO the requirement for the complete type is only required
for the final definition of f and g, which also seems to be intended as
described by the example of 7.1.5 p. 1. In principle these examples are also
not much different from constexpr function templates, which must delay the
evaluation until the concrete instantiation and usage (The last aspect becomes
clear by the 7.1.5 p. 1 example and demonstrates that this is a general
character of constexpr functions irrespective of templates).

[Bug c++/49015] [C++0x] Non-defining constexpr function declarations require complete argument/return types

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49015

--- Comment #1 from Jason Merrill <jason at gcc dot gnu.org> 2011-05-18 17:19:19 UTC ---
Author: jason
Date: Wed May 18 17:19:15 2011
New Revision: 173869

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=173869
Log:
    PR c++/48948
    PR c++/49015
    * class.c (finalize_literal_type_property): Do check
    for constexpr member functions of non-literal class.
    (finish_struct): Don't call check_deferred_constexpr_decls.
    * cp-tree.h: Don't declare it.
    (DECL_DEFERRED_CONSTEXPR_CHECK): Remove.
    * decl.c (grok_special_member_properties): Don't check it
    (grokfnedcl): Don't call validate_constexpr_fundecl.
    (start_preparsed_function): Do call it.
    * pt.c (tsubst_decl): Don't call it.
    (instantiate_class_template_1): Don't call
    check_deferred_constexpr_decls.
    * semantics.c (literal_type_p): Check for any incompleteness.
    (ensure_literal_type_for_constexpr_object): Likewise.
    (is_valid_constexpr_fn): Revert deferral changes.
    (validate_constexpr_fundecl): Likewise.
    (register_constexpr_fundef): Likewise.
    (check_deferred_constexpr_decls): Remove.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/constexpr-incomplete3.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/class.c
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/decl.c
    trunk/gcc/cp/pt.c
    trunk/gcc/cp/semantics.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/g++.dg/cpp0x/constexpr-incomplete2.C
    trunk/gcc/testsuite/g++.dg/cpp0x/constexpr-memfn1.C

[Bug c++/49015] [C++0x] Non-defining constexpr function declarations require complete argument/return types

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49015

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |jason at gcc dot gnu.org
         Resolution|                            |FIXED
         AssignedTo|unassigned at gcc dot       |jason at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> 2011-05-18 17:47:58 UTC ---
Fixed.