https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105061
Bug ID: 105061
Summary: [9/10 Regression] [c++2a+] anonymous bitfield
templated offset rejected
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: wjwray at gmail dot com
Target Milestone: ---
A very specific regression: https://godbolt.org/z/dWxnvd93j
template <typename alloc_unit, int width, int offset>
struct offset_bitfield { alloc_unit : offset, field : width; };
accepted forever with -std=c++17-
accepted in 9.4 with -std=c++2a
rejected in 10.1+ with -std=c++20+
(accepted in Clang & MSVC, any std)
My guess as to the cause: the c++20 change to allow bitfield initializers.
template <typename alloc_unit, int width, int offset>
struct offset_bitfield { alloc_unit : offset, field : width; };
// ^ ^
// error: found ':' in nested-name-specifier, expected '::'
// error: expected unqualified-id before ',' token
The template is accepted if the typename parameter is removed:
template <int width, int offset>
struct uint_offset_bitfield { unsigned : offset, field : width; };
