[Bug preprocessor/116047] New: C preprocessor bug

[ovidiu.panait at windriver dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116047

            Bug ID: 116047
           Summary: C preprocessor bug
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: preprocessor
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ovidiu.panait at windriver dot com
  Target Milestone: ---

When processing large header files, the C preprocessor reports error on the
wrong line.

This is 100% reproducible on my side with gcc mainline.

Reproducer:

# Build
mkdir build; cd build
../configure --host=x86_64-pc-linux-gnu --target=x86_64-wrs-linux
--enable-languages=c --disable-multilib --disable-libstdcxx-pch
--disable-libsanitizer --disable-libssp --disable-libquadmath
--disable-libquadmath-support --disable-libgomp --disable-libvtv
--disable-bootstrap
make all-host -j$(nproc)
mkdir install; make install-host DESTDIR=$(realpath ./install) -j$(nproc)


# Generate testcase
mkdir testcase; cd testcase
cat > main.c <<EOF
extern int main_begins;
extern int main_begins;
extern int main_begins;
#include "header1.h"
EOF
echo -n > header1.h
for i in {1..327676}; do
    echo "extern int header1_begins;" >> header1.h
done
cat >> header1.h <<EOF
#include "header2.h"
extern int header1 ends;
EOF
echo -n > header2.h


# Test
../install/usr/local/bin/x86_64-wrs-linux-gcc main.c
In file included from main.c:4:
header1.h:327677:20: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’
before ‘ends’
327677 | #include "header2.h"
       |                    ^


The line where the error is reported(327677) is bogus, the actual
error is on the next line(327678) in header1.h:

$ cat -n header1.h | tail -n3
327676    extern int header1_begins;
327677    #include "header2.h"
327678    extern int header1 ends;