Hi! My changes for "Module Declarations Shouldn’t 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. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk and 15.2? 2025-06-27 Jakub Jelinek <ja...@redhat.com> PR c++/120845 libcpp/ * lex.cc (cpp_maybe_module_directive): If premature CPP_PRAGMA_EOL is seen after CPP_NAME, back it up instead of dropping it. gcc/testsuite/ * g++.dg/modules/cpp-21.C: New test. --- libcpp/lex.cc.jj 2025-04-24 15:29:41.714893932 +0200 +++ libcpp/lex.cc 2025-06-27 12:19:23.593682734 +0200 @@ -3677,6 +3677,13 @@ cpp_maybe_module_directive (cpp_reader * break; } while (true); + if (peek->type == CPP_PRAGMA_EOL) + { + /* If we saw premature EOL, we want to keep it at this + point rather than drop it. See PR120845. */ + _cpp_backup_tokens_direct (pfile, backup); + backup = 0; + } } } else --- gcc/testsuite/g++.dg/modules/cpp-21.C.jj 2025-06-27 12:34:17.226227463 +0200 +++ gcc/testsuite/g++.dg/modules/cpp-21.C 2025-06-27 12:34:28.052088809 +0200 @@ -0,0 +1,8 @@ +// PR c++/120845 +// { dg-do compile } +// { dg-additional-options "-fmodules" } + +export module pr120485 + [[foobarbaz]]; +// { dg-error "expected ';' before end of line" "" { target *-*-* } .-2 } +// { dg-warning "attribute ignored" "" { target *-*-* } .-2 } Jakub
