https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126782
Bug ID: 126782
Summary: [Darwin] sys/_types/_rsize_t.h does not define rsize_t
with -fmodules
Product: gcc
Version: 16.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: hello at bjornpagen dot com
Target Milestone: ---
The macOS 26.2 SDK header sys/_types/_rsize_t.h contains this guard:
#if defined(__has_feature) && __has_feature(modules)
#define USE_CLANG_STDDEF 1
#else
#define USE_CLANG_STDDEF 0
#endif
The selected branch defines __need_rsize_t and includes <stddef.h>.
GCC 16.1.0 reports __has_feature(modules) as true with -fmodules. GCC's
stddef.h does not support the Clang __need_rsize_t protocol. The header
therefore does not define rsize_t. Declarations in the SDK's _string.h then
fail to parse.
The feature comes from flag_modules in gcc/cp/cp-objcp-common.cc. This behavior
is present in upstream GCC.
Minimal source:
#define __STDC_WANT_LIB_EXT1__ 1
#include <string.h>
rsize_t n;
Command:
g++-16 -std=c++26 -fmodules -c rsize.cc
Output:
_string.h:176:48: error: 'rsize_t' has not been declared; did you mean
'size_t'?
I attached the source and its preprocessed output.
Observed environment:
- GCC 16.1.0 release sources with the documented Darwin arm64 port series
- Build, host, and target: aarch64-apple-darwin24
- macOS 26.2 SDK from Xcode 26.3
- Configure command:
../gcc-16.1.0/configure \
--prefix=$HOME/.gcc/versions/16.1.0 \
--enable-languages=c,c++ \
--disable-nls \
--enable-checking=release \
--program-suffix=-16 \
--with-system-zlib \
--build=aarch64-apple-darwin24 \
--with-sysroot=<Xcode MacOSX.sdk>
The Darwin arm64 port is supporting context. The incorrect feature predicate is
upstream GCC behavior.
PR target/116827 covers the same SDK assumption for ptrdiff_t and size_t. Its
committed workaround does not implement __need_rsize_t. It does not fix this
testcase.
Expected result:
The SDK must define rsize_t. The source must compile with -fmodules.
Proposed fix:
A fixincludes rule changes the guard to require __clang__. GCC then uses the
SDK's plain typedef branch. Clang behavior does not change.
The rule has a narrow Darwin target pattern. Its bypass makes a second
fixincludes run produce no change. The patch includes a generated fixincl.x
file and a test fixture.
