https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120845
--- Comment #13 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-15 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:8193500f4fc97808ded2082428380e4f91d1a44a commit r15-10203-g8193500f4fc97808ded2082428380e4f91d1a44a Author: Jakub Jelinek <ja...@redhat.com> Date: Sun Aug 3 18:27:42 2025 +0200 libcpp: Fix up cpp_maybe_module_directive [PR120845] My changes for "Module Declarations Shouldnât be Macros" paper broke the following testcase. The backup handling intentionally tries to drop CPP_PRAGMA_EOL token if things go wrong, which is desirable for the case where we haven't committed to the module preprocessing directive (i.e. changed the first token to the magic one). In that case there is no preprocessing directive start and so CPP_PRAGMA_EOL would be wrong. If there is a premature new-line after we've changed the first token though, we shouldn't drop CPP_PRAGMA_EOL, because otherwise we ICE in the FE. While clang++ and MSVC accept the testcase, in my reading it is incorrect at least in the C++23 and newer wordings and I think the changes have been a DR, https://eel.is/c++draft/cpp.module has no exception for new-lines and https://eel.is/c++draft/cpp.pre#1.sentence-2 says that new-line (unless deleted during phase 2 when after backslash) ends the preprocessing directive. The patch arranges for eol being set only in the not_module case. 2025-08-03 Jakub Jelinek <ja...@redhat.com> PR c++/120845 libcpp/ * lex.cc (cpp_maybe_module_directive): Move eol variable declaration to the start of the function, initialize to false and only set it to peek->type == CPP_PRAGMA_EOL in the not_module case. Formatting fix. gcc/testsuite/ * g++.dg/modules/cpp-21.C: New test. (cherry picked from commit a68f416a706bc61bb323773295189c4ea413ffd6)
