Hi!
This patch implements C++23 P2334R1, which is easy because Joseph has done
all the hard work for C2X already.
Unlike the C N2645 paper, the C++ P2334R1 contains one important addition
(but not in the normative text):
"While this is a new preprocessor feature and cannot be treated as a defect
report, implementations that support older versions of the standard are
encouraged to implement this feature in the older language modes as well
as C++23."
so there are different variants how to implement it.
One is in the patch below, ignores that sentence and only implements it
for -std=c++23/-std=gnu++23 like it is only implemented for -std=c23.
Another option would be to implement it also in the older GNU modes but
not in the C/CXX modes (but it would be strange if we did that just for
C++ and not for C).
Yet another option is to enable it unconditionally.
And yet another option would be to enable it unconditionally but emit
a warning (or pedwarn) when it is seen.
Note, when it is enabled for the older language modes, as Joseph wrote
in the c11-elifdef-1.c testcase, it can result e.g. in rejecting previously
valid code:
#define A
#undef B
#if 0
#elifdef A
#error "#elifdef A applied"
#endif
#if 0
#elifndef B
#error "#elifndef B applied"
#endif
Note, seems clang went the enable it unconditionally in all standard
versions of both C and C++, no warnings or anything whatsoever, so
essentially treated it as a DR that changed behavior of e.g. the above code.
2021-10-05 Jakub Jelinek <ja...@redhat.com>
libcpp/
* init.c (lang_defaults): Implement P2334R1, enable elifdef for
-std=c++23 and -std=gnu++23.
gcc/testsuite/
* g++.dg/cpp/elifdef-1.C: New test.
* g++.dg/cpp/elifdef-2.C: New test.
* g++.dg/cpp/elifdef-3.C: New test.
--- libcpp/init.c.jj 2021-09-02 10:01:15.954715595 +0200
+++ libcpp/init.c 2021-10-05 09:55:15.010620700 +0200
@@ -122,8 +122,8 @@ static const struct lang_flags lang_defa
/* CXX17 */ { 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
1, 0, 1, 0, 1, 0, 0, 0 },
/* GNUCXX20 */ { 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1,
1, 0, 1, 1, 1, 0, 0, 0 },
/* CXX20 */ { 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
1, 0, 1, 1, 1, 0, 0, 0 },
- /* GNUCXX23 */ { 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1,
1, 0, 1, 1, 1, 0, 1, 0 },
- /* CXX23 */ { 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 0, 1, 1, 1, 0, 1, 0 },
+ /* GNUCXX23 */ { 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1,
1, 0, 1, 1, 1, 0, 1, 1 },
+ /* CXX23 */ { 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 0, 1, 1, 1, 0, 1, 1 },
/* ASM */ { 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0 }
};
--- gcc/testsuite/g++.dg/cpp/elifdef-1.C.jj 2021-10-05 10:00:41.410057024
+0200
+++ gcc/testsuite/g++.dg/cpp/elifdef-1.C 2021-10-05 10:00:33.110173069
+0200
@@ -0,0 +1,3 @@
+// { dg-do preprocess { target { ! c++23 } } }
+
+#include "../../gcc.dg/cpp/c11-elifdef-1.c"
--- gcc/testsuite/g++.dg/cpp/elifdef-2.C.jj 2021-10-05 10:01:30.345372808
+0200
+++ gcc/testsuite/g++.dg/cpp/elifdef-2.C 2021-10-05 10:03:36.560608083
+0200
@@ -0,0 +1,4 @@
+// P2334R1
+// { dg-do preprocess { target c++23 } }
+
+#include "../../gcc.dg/cpp/c2x-elifdef-1.c"
--- gcc/testsuite/g++.dg/cpp/elifdef-3.C.jj 2021-10-05 10:01:36.029293338
+0200
+++ gcc/testsuite/g++.dg/cpp/elifdef-3.C 2021-10-05 10:03:48.896435601
+0200
@@ -0,0 +1,4 @@
+// P2334R1
+// { dg-do preprocess { target c++23 } }
+
+#include "../../gcc.dg/cpp/c2x-elifdef-1.c"
Jakub
