https://gcc.gnu.org/g:b9f443b6177881c490fbce9ba65b86a7cd65f11f
commit r16-2747-gb9f443b6177881c490fbce9ba65b86a7cd65f11f
Author: Jakub Jelinek <ja...@redhat.com>
Date: Mon Aug 4 14:27:14 2025 +0200
libcpp: Use pedwarn instead of warning for CWG2578 diagnostics [PR120778]
This is another case which changed from compile time undefined behavior
to ill-formed, diagnostic required. Now, we warn on this, so pedantically
that is good enough, maybe all we need is a testcase, but the following
patch changes it to a pedwarn for C++26.
2025-08-04 Jakub Jelinek <ja...@redhat.com>
PR preprocessor/120778
* macro.cc (stringify_arg): For C++26 emit a pedarn instead of
warning
for \ at the end of stringification.
* g++.dg/DRs/dr2578.C: New test.
Diff:
---
gcc/testsuite/g++.dg/DRs/dr2578.C | 10 ++++++++++
libcpp/macro.cc | 5 ++++-
2 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/gcc/testsuite/g++.dg/DRs/dr2578.C
b/gcc/testsuite/g++.dg/DRs/dr2578.C
new file mode 100644
index 000000000000..0dce23b94649
--- /dev/null
+++ b/gcc/testsuite/g++.dg/DRs/dr2578.C
@@ -0,0 +1,10 @@
+// DR 2578 - Undefined behavior when creating an invalid string literal via
stringizing
+// { dg-do preprocess }
+// { dg-options "-pedantic-errors" }
+
+#define A(a) #a
+#define B(a) A(a)
+#define C \\
+
+const char *x = B(C); // { dg-warning "invalid string literal, ignoring final
'\\\\'" "" { target c++23_down } }
+// { dg-error "invalid string literal, ignoring final '\\\\'" "" { target
c++26 } .-1 }
diff --git a/libcpp/macro.cc b/libcpp/macro.cc
index be2571034718..d869b0239350 100644
--- a/libcpp/macro.cc
+++ b/libcpp/macro.cc
@@ -1003,7 +1003,10 @@ stringify_arg (cpp_reader *pfile, const cpp_token
**first, unsigned int count)
/* Ignore the final \ of invalid string literals. */
if (backslash_count & 1)
{
- cpp_error (pfile, CPP_DL_WARNING,
+ cpp_error (pfile,
+ CPP_OPTION (pfile, cplusplus)
+ && CPP_OPTION (pfile, lang) >= CLK_GNUCXX26
+ ? CPP_DL_PEDWARN : CPP_DL_WARNING,
"invalid string literal, ignoring final %<\\%>");
dest--;
}
