Re: Avoid gnulib redefinitions - MDA, free-posix

[Gavin Smith <gavinsmith0123@gmail.com>]

On Sat, Oct 29, 2022 at 09:58:25AM -0700, Paul Eggert wrote:
> If it's just 'free', I might prefer the latter solution, to underline the
> special case and to avoid even more complexity in gnulib-tool. Is that
> something you could write?

Here is a first attempt.  I am not very familiar with the Gnulib code.

The main idea is to put a define in AM_CPPFLAGS in the Makefile that
gnulib-tool generates.  Then the gnulib headers can distinguish whether
they are being used as part of building gnulib, or building the user's
program.

This avoided looking through all the gnulib code and deciding where
to replace "free" with "gl_internal_free" or whatever the replacement
would be called.

I tried to minimize the number of lines of code that would change, but
if this approach was adopted, then the following changes should also be
made:
* Rename free-posix to free-posix-internal and free-posix-public to free-posix
* REPLACE_FREE to be changed to REPLACE_FREE_INTERNAL throughout gnulib,
  likewise REPACE_FREE_PUBLIC to REPLACE_FREE.

I tested this on a project with a gnulib import.

Let me know if this is the right approach and if there are changes to
make to the patch.

diff --git a/ChangeLog b/ChangeLog
index 6f4bea5c1c..994f457e70 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,21 @@
+2020-10-29  Gavin Smith  <gavinsmith0123@gmail.com>
+
+	Avoid unrequested 'free' redefinition
+
+	* gnulib-tool (func_emit_lib_Makefile_am):
+	Add -DGNULIB_INTERNAL to AM_CPPFLAGS.
+	* m4/free-public.m4, modules/free-posix-public:
+	New module to set @REPLACE_FREE_PUBLIC@ from @REPLACE_FREE@.
+	* modules/stdlib, m4/stdlib_h.m4:
+	Substitute for @REPLACE_FREE_PUBLIC@.
+	* lib/stdlib.in.h <@GNULIB_FREE_POSIX@>: Only replace 'free' if
+	both GNULIB_INTERNAL and @REPLACE_FREE@ are set, or if
+	@REPLACE_FREE_PUBLIC@ is set.
+
+	This allows Gnulib to use the free redefinition internally without
+	replacing it in user code, unless they explicitly request the
+	module.
+
 2022-10-23  Bruno Haible  <bruno@clisp.org>
 
 	assert-h: Make static_assert work on Solaris 11.4.
diff --git a/gnulib-tool b/gnulib-tool
index 028bcf36ad..84a77171d7 100755
--- a/gnulib-tool
+++ b/gnulib-tool
@@ -3945,7 +3945,7 @@ func_emit_lib_Makefile_am ()
   fi
   if test -z "$makefile_name"; then
     echo
-    echo "AM_CPPFLAGS =$cppflags_part1$cppflags_part2"
+    echo "AM_CPPFLAGS = -DGNULIB_INTERNAL$cppflags_part1$cppflags_part2"
     echo "AM_CFLAGS ="
   else
     if test -n "$cppflags_part1$cppflags_part2"; then
diff --git a/lib/stdlib.in.h b/lib/stdlib.in.h
index 8e0a609f1f..f75b8621f4 100644
--- a/lib/stdlib.in.h
+++ b/lib/stdlib.in.h
@@ -179,7 +179,7 @@ _GL_WARN_ON_USE (_Exit, "_Exit is unportable - "
 
 
 #if @GNULIB_FREE_POSIX@
-# if @REPLACE_FREE@
+# if @REPLACE_FREE@ && defined(GNULIB_INTERNAL) || @REPLACE_FREE_PUBLIC@
 #  if !(defined __cplusplus && defined GNULIB_NAMESPACE)
 #   undef free
 #   define free rpl_free
diff --git a/m4/free-public.m4 b/m4/free-public.m4
new file mode 100644
index 0000000000..497abf81ae
--- /dev/null
+++ b/m4/free-public.m4
@@ -0,0 +1 @@
+AC_DEFUN([gl_PREREQ_FREE_PUBLIC], [:])
diff --git a/m4/stdlib_h.m4 b/m4/stdlib_h.m4
index 9e2096976f..b096054284 100644
--- a/m4/stdlib_h.m4
+++ b/m4/stdlib_h.m4
@@ -171,6 +171,7 @@ AC_DEFUN([gl_STDLIB_H_DEFAULTS],
   REPLACE_CALLOC_FOR_CALLOC_POSIX=0;  AC_SUBST([REPLACE_CALLOC_FOR_CALLOC_POSIX])
   REPLACE_CANONICALIZE_FILE_NAME=0;  AC_SUBST([REPLACE_CANONICALIZE_FILE_NAME])
   REPLACE_FREE=0;            AC_SUBST([REPLACE_FREE])
+  REPLACE_FREE_PUBLIC=0;     AC_SUBST([REPLACE_FREE_PUBLIC])
   REPLACE_INITSTATE=0;       AC_SUBST([REPLACE_INITSTATE])
   REPLACE_MALLOC_FOR_MALLOC_GNU=0;    AC_SUBST([REPLACE_MALLOC_FOR_MALLOC_GNU])
   REPLACE_MALLOC_FOR_MALLOC_POSIX=0;  AC_SUBST([REPLACE_MALLOC_FOR_MALLOC_POSIX])
diff --git a/modules/free-posix-public b/modules/free-posix-public
new file mode 100644
index 0000000000..050a06bf76
--- /dev/null
+++ b/modules/free-posix-public
@@ -0,0 +1,27 @@
+Description:
+Work around systems where free clobbers errno.
+
+Files:
+m4/free-public.m4
+
+Depends-on:
+free-posix
+
+configure.ac:
+REPLACE_FREE_PUBLIC=$REPLACE_FREE
+gl_CONDITIONAL([GL_COND_OBJ_FREE_PUBLIC], [test $REPLACE_FREE_PUBLIC = 1])
+AM_COND_IF([GL_COND_OBJ_FREE_PUBLIC], [
+  gl_PREREQ_FREE_PUBLIC
+])
+gl_STDLIB_MODULE_INDICATOR([free-posix-public])
+
+Makefile.am:
+
+Include:
+<stdlib.h>
+
+License:
+LGPLv2+
+
+Maintainer:
+None
diff --git a/modules/stdlib b/modules/stdlib
index 45d8f59331..2266e68d52 100644
--- a/modules/stdlib
+++ b/modules/stdlib
@@ -131,6 +131,7 @@ stdlib.h: stdlib.in.h $(top_builddir)/config.status $(CXXDEFS_H) \
 	      -e 's|@''REPLACE_CALLOC_FOR_CALLOC_POSIX''@|$(REPLACE_CALLOC_FOR_CALLOC_POSIX)|g' \
 	      -e 's|@''REPLACE_CANONICALIZE_FILE_NAME''@|$(REPLACE_CANONICALIZE_FILE_NAME)|g' \
 	      -e 's|@''REPLACE_FREE''@|$(REPLACE_FREE)|g' \
+	      -e 's|@''REPLACE_FREE_PUBLIC''@|$(REPLACE_FREE_PUBLIC)|g' \
 	      -e 's|@''REPLACE_INITSTATE''@|$(REPLACE_INITSTATE)|g' \
 	      -e 's|@''REPLACE_MALLOC_FOR_MALLOC_GNU''@|$(REPLACE_MALLOC_FOR_MALLOC_GNU)|g' \
 	      -e 's|@''REPLACE_MALLOC_FOR_MALLOC_POSIX''@|$(REPLACE_MALLOC_FOR_MALLOC_POSIX)|g' \