https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102229
--- Comment #12 from CVS Commits ---
The releases/gcc-11 branch has been updated by Marek Polacek
:
https://gcc.gnu.org/g:24ee44c37a28eae80430a1ad86ffb0923446db2d
commit r11-9430-g24ee44c37a28eae80430a1ad86ffb0923446db2d
Author: Marek Polacek
Date: Fri Dec 10 15:38:35 2021 -0500
c++: Allow constexpr decltype(auto) [PR102229]
My r11-2202 was trying to enforce [dcl.type.auto.deduct]/4, which says
"If the placeholder-type-specifier is of the form type-constraint[opt]
decltype(auto), T shall be the placeholder alone." But this made us
reject 'constexpr decltype(auto)', which, after clarification from CWG,
should be valid. [dcl.type.auto.deduct]/4 is supposed to be a syntactic
constraint, not semantic, so it's OK that the constexpr marks the object
as const.
As a consequence, checking TYPE_QUALS in do_auto_deduction is too late,
and we have a FIXME there anyway. So in this patch I'm attempting to
detect 'const decltype(auto)' earlier. If I'm going to use TYPE_QUALS,
it needs to happen before we mark the object as const due to constexpr,
that is, before grokdeclarator's
/* A `constexpr' specifier used in an object declaration declares
the object as `const'. */
if (constexpr_p && innermost_code != cdk_function)
...
Constrained decltype(auto) was a little problem, hence the TYPENAME
check. But in a typename context you can't use decltype(auto) anyway,
I think.
PR c++/102229
gcc/cp/ChangeLog:
* decl.c (check_decltype_auto): New.
(grokdeclarator): Call it.
* pt.c (do_auto_deduction): Don't check decltype(auto) here.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/decltype-auto5.C: New test.
(cherry picked from commit 06d5dcef72542baf49ac245cfde2ad7ecef0916b)
