Hi Bruno,
Bruno Haible <br...@clisp.org> writes:
> I agree that when the system has a working implementation of a .h file,
> we should interfere with it to the least possible amount.
>
> But the problem here is
> 1) The term "working implementation" depends on the language in effect.
> It may be working C and not working in C++ — that is the case that
> Collin observed with GCC 15.
> Or it may be working in C++ and not working in C — that is another
> case.
> 2) The standards may extend the expected contents of <stdckdint.h>
> in the future. In that case, our current dichotomy of "generate
> the file" or "not generate the file" would break down as well.
>
> I would therefore propose a more future-proof approach: based on the same
> approach as we have been taken for so many other .h files.
>
> 1) In lib/stdckdint.in.h include the system's .h file if it exists,
> via include_next. (Fortunately all known compilers that have 2 copies
> of stdckdint.h support include_next. The fallback with
> #include "absolute file name of stdckdint.h"
> will work with other compilers.)
> 2) Parameterize this file with 4 AC_SUBSTed variables:
> - one that tells whether the C compiler has <stdckdint.h>,
> - one that tells whether the <stdckdint.h> seen by the C compiler
> is complete (in the sense that it provides all that the GNU
> replacement would do),
> - one that tells whether the C++ compiler has <stdckdint.h>,
> - one that tells whether the <stdckdint.h> seen by the C++ compiler
> is complete.
> 3) In the .m4 code, make two C compiler invocations to determine the
> first two of these values and - if $CXX != no - two C++ compiler
> invocations to determine the other two values.
> 4) Determine GL_GENERATE_STDCKDINT_H based on these 4 values.
>
> This way, we would be prepared for changes in the standards, bugs in
> specific compilers, and handle C++ independently from C (which seems
> to be required in this case).
Can you check the attached patch? I think it matches what you said
above.
With GCC 15 and C++26 the result is (*):
$ ./configure CFLAGS='-std=gnu99' CXXFLAGS='-std=gnu++26' | grep stdckdint
checking for stdckdint.h... yes
checking whether stdckdint.h can be included in C... yes
checking whether stdckdint.h defines ckd_add, ckd_sub, ckd_mul in C... yes
checking whether stdckdint.h can be included in C++... yes
checking whether stdckdint.h defines ckd_add, ckd_sub, ckd_mul in C++... yes
$ make
$ ls gllib/stdckdint.h
ls: cannot access 'gllib/stdckdint.h': No such file or directory
And with GCC 15 and C++14:
$ ./configure CFLAGS='-std=gnu99' CXXFLAGS='-std=gnu++14' | grep stdckdint
checking for stdckdint.h... yes
checking whether stdckdint.h can be included in C... yes
checking whether stdckdint.h defines ckd_add, ckd_sub, ckd_mul in C... yes
checking whether stdckdint.h can be included in C++... yes
checking whether stdckdint.h defines ckd_add, ckd_sub, ckd_mul in C++... no
$ make
$ ls gllib/stdckdint.h
gllib/stdckdint.h
In the second case, when compiling a C program <stdckdint.h> simply does
an #include_next.
Collin
(*) I find it strange that the C++ declarations are hidden depending on
the C++ standard, but the C ones are not. I would expect -std=(gnu|c)99
to disable them like the C++ version.
>From 97dbb1f1a349c4817e91ed2b5fcc5c30b484360b Mon Sep 17 00:00:00 2001
Message-ID: <97dbb1f1a349c4817e91ed2b5fcc5c30b484360b.1747882664.git.collin.fu...@gmail.com>
From: Collin Funk <collin.fu...@gmail.com>
Date: Wed, 21 May 2025 19:55:47 -0700
Subject: [PATCH] stdckdint-h: Don't generate header if it is not needed.
Suggested by Paul Eggert in:
<https://lists.gnu.org/archive/html/bug-gnulib/2025-05/msg00216.html>.
* m4/stdckdint_h.m4: New file.
* modules/stdckdint-h (Files): Add m4/stdckdint_h.m4.
(configure.ac): Remove checks and just invoke gl_STDCKDINT_H.
(Makefile.am): Replace variables set by ./configure.
* lib/stdckdint.in.h: Include the compilers header if it exists.
(ckd_add, ckd_sub, ckd_mul): Only define if the compilers definitions do
not work.
---
ChangeLog | 13 +++++
lib/stdckdint.in.h | 31 +++++++---
m4/stdckdint_h.m4 | 136 ++++++++++++++++++++++++++++++++++++++++++++
modules/stdckdint-h | 21 +++----
4 files changed, 184 insertions(+), 17 deletions(-)
create mode 100644 m4/stdckdint_h.m4
diff --git a/ChangeLog b/ChangeLog
index b85c7c6e6e..f946fc5d91 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,16 @@
+2025-05-21 Collin Funk <collin.fu...@gmail.com>
+
+ stdckdint-h: Don't generate header if it is not needed.
+ Suggested by Paul Eggert in:
+ <https://lists.gnu.org/archive/html/bug-gnulib/2025-05/msg00216.html>.
+ * m4/stdckdint_h.m4: New file.
+ * modules/stdckdint-h (Files): Add m4/stdckdint_h.m4.
+ (configure.ac): Remove checks and just invoke gl_STDCKDINT_H.
+ (Makefile.am): Replace variables set by ./configure.
+ * lib/stdckdint.in.h: Include the compilers header if it exists.
+ (ckd_add, ckd_sub, ckd_mul): Only define if the compilers definitions do
+ not work.
+
2025-05-19 Collin Funk <collin.fu...@gmail.com>
stdckdint-h: Work around missing declarations with g++ 15.0.
diff --git a/lib/stdckdint.in.h b/lib/stdckdint.in.h
index 83277b728e..2d317b9588 100644
--- a/lib/stdckdint.in.h
+++ b/lib/stdckdint.in.h
@@ -15,10 +15,26 @@
You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
-#ifndef _GL_STDCKDINT_H
-#define _GL_STDCKDINT_H
+#ifndef _@GUARD_PREFIX@_STDCKDINT_H
-#include "intprops-internal.h"
+#if __GNUC__ >= 3
+@PRAGMA_SYSTEM_HEADER@
+#endif
+@PRAGMA_COLUMNS@
+
+#if defined __cplusplus ? @HAVE_CXX_STDCKDINT_H@ : @HAVE_C_STDCKDINT_H@
+#@INCLUDE_NEXT@ @NEXT_STDCKDINT_H@
+#endif
+
+/* Do nothing but include the system header if it works properly. */
+#if defined __cplusplus ? @HAVE_WORKING_CXX_STDCKDINT_H@ : @HAVE_WORKING_C_STDCKDINT_H@
+
+/* Avoid redefining macros. */
+# undef ckd_add
+# undef ckd_sub
+# undef ckd_mul
+
+# include "intprops-internal.h"
/* Store into *R the low-order bits of A + B, A - B, A * B, respectively.
Return 1 if the result overflows, 0 otherwise.
@@ -28,8 +44,9 @@
These are like the standard macros introduced in C23, except that
arguments should not have side effects. */
-#define ckd_add(r, a, b) ((bool) _GL_INT_ADD_WRAPV (a, b, r))
-#define ckd_sub(r, a, b) ((bool) _GL_INT_SUBTRACT_WRAPV (a, b, r))
-#define ckd_mul(r, a, b) ((bool) _GL_INT_MULTIPLY_WRAPV (a, b, r))
+# define ckd_add(r, a, b) ((bool) _GL_INT_ADD_WRAPV (a, b, r))
+# define ckd_sub(r, a, b) ((bool) _GL_INT_SUBTRACT_WRAPV (a, b, r))
+# define ckd_mul(r, a, b) ((bool) _GL_INT_MULTIPLY_WRAPV (a, b, r))
-#endif /* _GL_STDCKDINT_H */
+#endif /* defined __cplusplus ? @HAVE_WORKING_CXX_STDCKDINT_H@ : @HAVE_WORKING_C_STDCKDINT_H@ */
+#endif /* _@GUARD_PREFIX@_STDCKDINT_H */
diff --git a/m4/stdckdint_h.m4 b/m4/stdckdint_h.m4
new file mode 100644
index 0000000000..f8e99a1920
--- /dev/null
+++ b/m4/stdckdint_h.m4
@@ -0,0 +1,136 @@
+# stdckdint_h.m4
+# serial 1
+dnl Copyright 2025 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+dnl This file is offered as-is, without any warranty.
+
+dnl Written by Collin Funk.
+
+AC_DEFUN_ONCE([gl_STDCKDINT_H],
+[
+ gl_CHECK_NEXT_HEADERS([stdckdint.h])
+ if test $ac_cv_header_stdckdint_h = yes; then
+ HAVE_STDCKDINT_H=1
+ else
+ HAVE_STDCKDINT_H=0
+ fi
+ AC_SUBST([HAVE_STDCKDINT_H])
+
+ if test $HAVE_STDCKDINT_H == 1; then
+ AC_CACHE_CHECK([whether stdckdint.h can be included in C],
+ [gl_cv_header_c_stdckdint_h],
+ [AC_COMPILE_IFELSE(
+ [AC_LANG_PROGRAM(
+ [[#include <stdckdint.h>
+ ]])],
+ [gl_cv_header_c_stdckdint_h=yes],
+ [gl_cv_header_c_stdckdint_h=no])])
+ if test $gl_cv_header_c_stdckdint_h = yes; then
+ HAVE_C_STDCKDINT_H=1
+ AC_CACHE_CHECK([whether stdckdint.h defines ckd_add, ckd_sub, ckd_mul in C],
+ [gl_cv_header_c_stdckdint_h_works],
+ [AC_COMPILE_IFELSE(
+ [AC_LANG_PROGRAM(
+ [[#include <stdckdint.h>
+ ]],
+ [[int r;
+ int a = 1;
+ int b = 1;
+ return !!(ckd_add (&r, a, b) || ckd_sub (&r, a, b)
+ || ckd_mul (&r, a, b));
+ ]])],
+ [gl_cv_header_c_stdckdint_h_works=yes],
+ [gl_cv_header_c_stdckdint_h_works=no])])
+ if test $gl_cv_header_c_stdckdint_h_works = yes; then
+ HAVE_WORKING_C_STDCKDINT_H=1
+ else
+ HAVE_WORKING_C_STDCKDINT_H=0
+ fi
+ else
+ HAVE_C_STDCKDINT_H=0
+ HAVE_WORKING_C_STDCKDINT_H=0
+ fi
+ if test "$CXX" != no; then
+ AC_CACHE_CHECK([whether stdckdint.h can be included in C++],
+ [gl_cv_header_cxx_stdckdint_h],
+ [dnl We can't use AC_LANG_PUSH([C++]) and AC_LANG_POP([C++]) here, due to
+ dnl an autoconf bug <https://savannah.gnu.org/support/?110294>.
+ cat > conftest.cpp <<\EOF
+#include <stdckdint.h>
+EOF
+ gl_command="$CXX $CXXFLAGS $CPPFLAGS -c conftest.cpp"
+ if AC_TRY_EVAL([gl_command]); then
+ gl_cv_header_cxx_stdckdint_h=yes
+ else
+ gl_cv_header_cxx_stdckdint_h=no
+ fi
+ rm -fr conftest*
+ ])
+ if test $gl_cv_header_cxx_stdckdint_h = yes; then
+ HAVE_CXX_STDCKDINT_H=1
+ AC_CACHE_CHECK([whether stdckdint.h defines ckd_add, ckd_sub, ckd_mul in C++],
+ [gl_cv_header_cxx_stdckdint_h_works],
+ [dnl We can't use AC_LANG_PUSH([C++]) and AC_LANG_POP([C++]) here, due to
+ dnl an autoconf bug <https://savannah.gnu.org/support/?110294>.
+ cat > conftest.cpp <<\EOF
+#include <stdckdint.h>
+int
+main (void)
+{
+ int r;
+ int a = 1;
+ int b = 1;
+ return !!(ckd_add (&r, a, b) || ckd_sub (&r, a, b) || ckd_mul (&r, a, b));
+}
+EOF
+ gl_command="$CXX $CXXFLAGS $CPPFLAGS -c conftest.cpp"
+ if AC_TRY_EVAL([gl_command]); then
+ gl_cv_header_cxx_stdckdint_h_works=yes
+ else
+ gl_cv_header_cxx_stdckdint_h_works=no
+ fi
+ rm -fr conftest*
+ ])
+ if test $gl_cv_header_cxx_stdckdint_h_works = yes; then
+ HAVE_WORKING_CXX_STDCKDINT_H=1
+ else
+ HAVE_WORKING_CXX_STDCKDINT_H=0
+ fi
+ else
+ HAVE_CXX_STDCKDINT_H=0
+ HAVE_WORKING_CXX_STDCKDINT_H=0
+ fi
+ fi
+ else
+ HAVE_C_STDCKDINT_H=0
+ HAVE_WORKING_C_STDCKDINT_H=0
+ HAVE_CXX_STDCKDINT_H=0
+ HAVE_WORKING_CXX_STDCKDINT_H=0
+ fi
+ AC_SUBST([HAVE_C_STDCKDINT_H])
+ AC_SUBST([HAVE_WORKING_C_STDCKDINT_H])
+ AC_SUBST([HAVE_CXX_STDCKDINT_H])
+ AC_SUBST([HAVE_WORKING_CXX_STDCKDINT_H])
+
+ if test "$CXX" != no; then
+ dnl We might need the header for C or C++.
+ if test $HAVE_C_STDCKDINT_H = 1 \
+ && test $HAVE_WORKING_C_STDCKDINT_H = 1 \
+ && test $HAVE_CXX_STDCKDINT_H = 1 \
+ && test $HAVE_WORKING_CXX_STDCKDINT_H = 1; then
+ GL_GENERATE_STDCKDINT_H=false
+ else
+ GL_GENERATE_STDCKDINT_H=true
+ fi
+ else
+ dnl We don't care about C++ here.
+ if test $HAVE_C_STDCKDINT_H = 1 \
+ && test $HAVE_WORKING_C_STDCKDINT_H = 1; then
+ GL_GENERATE_STDCKDINT_H=false
+ else
+ GL_GENERATE_STDCKDINT_H=true
+ fi
+ fi
+])
diff --git a/modules/stdckdint-h b/modules/stdckdint-h
index ff777d8d62..7f7c612bce 100644
--- a/modules/stdckdint-h
+++ b/modules/stdckdint-h
@@ -2,6 +2,7 @@ Description:
An <stdckdint.h> that is like C23.
Files:
+m4/stdckdint_h.m4
lib/stdckdint.in.h
lib/intprops-internal.h
@@ -10,16 +11,7 @@ gen-header
bool
configure.ac:
-AC_CHECK_HEADERS_ONCE([stdckdint.h])
-if test $ac_cv_header_stdckdint_h = yes; then
- if test -n "$CXX" && test "$CXX" != no; then
- GL_GENERATE_STDCKDINT_H=true
- else
- GL_GENERATE_STDCKDINT_H=false
- fi
-else
- GL_GENERATE_STDCKDINT_H=true
-fi
+gl_STDCKDINT_H
gl_CONDITIONAL_HEADER([stdckdint.h])
AC_PROG_MKDIR_P
@@ -32,6 +24,15 @@ if GL_GENERATE_STDCKDINT_H
stdckdint.h: stdckdint.in.h $(top_builddir)/config.status
@NMD@ $(AM_V_GEN)$(MKDIR_P) '%reldir%'
$(gl_V_at)$(SED_HEADER_STDOUT) \
+ -e 's|@''GUARD_PREFIX''@|${gl_include_guard_prefix}|g' \
+ -e 's|@''INCLUDE_NEXT''@|$(INCLUDE_NEXT)|g' \
+ -e 's|@''PRAGMA_SYSTEM_HEADER''@|@PRAGMA_SYSTEM_HEADER@|g' \
+ -e 's|@''PRAGMA_COLUMNS''@|@PRAGMA_COLUMNS@|g' \
+ -e 's|@''NEXT_STDCKDINT_H''@|$(NEXT_STDCKDINT_H)|g' \
+ -e 's|@''HAVE_C_STDCKDINT_H''@|$(HAVE_C_STDCKDINT_H)|g' \
+ -e 's|@''HAVE_WORKING_C_STDCKDINT_H''@|$(HAVE_WORKING_C_STDCKDINT_H)|g' \
+ -e 's|@''HAVE_CXX_STDCKDINT_H''@|$(HAVE_CXX_STDCKDINT_H)|g' \
+ -e 's|@''HAVE_WORKING_CXX_STDCKDINT_H''@|$(HAVE_WORKING_CXX_STDCKDINT_H)|g' \
$(srcdir)/stdckdint.in.h > $@-t
$(AM_V_at)mv $@-t $@
else
--
2.49.0
