This is odd behavior, but just annoying. If I create a pch this way: %COMP.sh "-x c++-header -Winvalid-pch" ostream I get: ostream:43:13: warning: #pragma system_header ignored outside include file However, if I create a pch by doing cat > precomp_ostream.hh #include <ostream> I don't get the error. These cases, which are identical input, should give identical output. Release: gcc-3.4 20030125 Environment: rh linux 7.3
Assigning to PCH expert: still happens (20030525): tin:~/src/gnu/gcctest>g++ -x c++-header -Winvalid-pch /home/gates/pinskia/linux/include/ c++/3.4/ostream /home/gates/pinskia/linux/include/c++/3.4/ostream:43:13: warning: #pragma system_header ignored outside include file
Simple testcase: testsys.h: #pragma GCC system_header g++ -ansi -Werror -pedantic -Winvalid-pch -o testsys.h.gch -c testsys.h testsys.h:1:14: #pragma system_header ignored outside include file
Although the simplified testcase still works, note that with an installed compiler saying g++ -x c++-header ostream will say 'file not found' unless there is actually an ostream in the current directory.
I think this same problem will occur with #include_next and #pragma once. cpp doesn't currently seem to differentiate between the PCH case and other kinds of preprocessing.
The master branch has been updated by Lewis Hyatt <lhyatt@gcc.gnu.org>: https://gcc.gnu.org/g:9938645fcf914ec2a3fa8137cf1456ad4af5f77c commit r14-5471-g9938645fcf914ec2a3fa8137cf1456ad4af5f77c Author: Lewis Hyatt <lhyatt@gmail.com> Date: Fri Nov 10 11:10:18 2023 -0500 c-family: Let libcpp know when the compilation is for a PCH [PR9471] libcpp will generate diagnostics when it encounters things in the main file that only belong in a header file, such as `#pragma once' or `#pragma GCC system_header'. But sometimes the main file is a header file that is just being compiled separately, e.g. to produce a C++ module or a PCH, in which case such diagnostics should be suppressed. libcpp already has an interface to request that, so make use of it in the C frontends to prevent libcpp from issuing unwanted diagnostics when compiling a PCH. gcc/c-family/ChangeLog: PR pch/9471 PR pch/47857 * c-opts.cc (c_common_post_options): Set cpp_opts->main_search so libcpp knows it is compiling a header file separately. gcc/testsuite/ChangeLog: PR pch/9471 PR pch/47857 * g++.dg/pch/main-file-warnings.C: New test. * g++.dg/pch/main-file-warnings.Hs: New test. * gcc.dg/pch/main-file-warnings.c: New test. * gcc.dg/pch/main-file-warnings.hs: New test.
Fixed for GCC 14.