Re: Annoying build warnings from latest Apple toolchain

I wrote:
> So I experimented with fixing things so that the versions of these
> functions exported by libpq have physically different names from those
> that you'd get from linking to libpgcommon.a or libpgcommon_srv.a.
> Then, there's certainty about which one a given usage will link to,
> based on what the #define environment is when the call is compiled.

> This leads to a pleasingly small patch, at least in the Makefile
> universe (I've not attempted to sync the meson or MSVC infrastructure
> with this yet).

Here's a v2 that addresses the meson infrastructure as well.
(This is my first attempt at writing meson code, so feel free
to critique.)  I propose not bothering to fix src/tools/msvc/,
on the grounds that (a) that infrastructure will likely be gone
before v17 ships, and (b) the latent problem with version
skew between libpq.dll and calling programs seems much less
likely to matter in the Windows world in the first place.

Barring comments or CI failures, I intend to push this soon.

            regards, tom lane

diff --git a/src/bin/initdb/Makefile b/src/bin/initdb/Makefile
index d69bd89572..e80e57e457 100644
--- a/src/bin/initdb/Makefile
+++ b/src/bin/initdb/Makefile
@@ -16,13 +16,12 @@ subdir = src/bin/initdb
 top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global

-override CPPFLAGS := -I$(libpq_srcdir) -I$(top_srcdir)/src/timezone $(ICU_CFLAGS) $(CPPFLAGS)
-
 # Note: it's important that we link to encnames.o from libpgcommon, not
 # from libpq, else we have risks of version skew if we run with a libpq
-# shared library from a different PG version.  The libpq_pgport macro
-# should ensure that that happens.
-#
+# shared library from a different PG version.  Define
+# USE_PRIVATE_ENCODING_FUNCS to ensure that that happens.
+override CPPFLAGS := -DUSE_PRIVATE_ENCODING_FUNCS -I$(libpq_srcdir) -I$(top_srcdir)/src/timezone $(ICU_CFLAGS)
$(CPPFLAGS)
+
 # We need libpq only because fe_utils does.
 LDFLAGS_INTERNAL += -L$(top_builddir)/src/fe_utils -lpgfeutils $(libpq_pgport) $(ICU_LIBS)

diff --git a/src/bin/initdb/meson.build b/src/bin/initdb/meson.build
index 49743630aa..28a2df99e4 100644
--- a/src/bin/initdb/meson.build
+++ b/src/bin/initdb/meson.build
@@ -7,19 +7,25 @@ initdb_sources = files(

 initdb_sources += timezone_localtime_source

-#fixme: reimplement libpq_pgport logic
-
 if host_system == 'windows'
   initdb_sources += rc_bin_gen.process(win32ver_rc, extra_args: [
     '--NAME', 'initdb',
     '--FILEDESC', 'initdb - initialize a new database cluster',])
 endif

+# Note: it's important that we link to encnames.o from libpgcommon, not
+# from libpq, else we have risks of version skew if we run with a libpq
+# shared library from a different PG version.  Define
+# USE_PRIVATE_ENCODING_FUNCS to ensure that that happens.
+c_args = default_bin_args.get('c_args', []) + ['-DUSE_PRIVATE_ENCODING_FUNCS']
+
 initdb = executable('initdb',
   initdb_sources,
   include_directories: [timezone_inc],
   dependencies: [frontend_code, libpq, icu, icu_i18n],
-  kwargs: default_bin_args,
+  kwargs: default_bin_args + {
+    'c_args': c_args,
+  },
 )
 bin_targets += initdb

diff --git a/src/common/Makefile b/src/common/Makefile
index cc5c54dcee..70884be00c 100644
--- a/src/common/Makefile
+++ b/src/common/Makefile
@@ -140,6 +140,13 @@ libpgcommon.a: $(OBJS_FRONTEND)
     rm -f $@
     $(AR) $(AROPT) $@ $^

+#
+# Files in libpgcommon.a should use/export the "xxx_private" versions
+# of pg_char_to_encoding() and friends.
+#
+$(OBJS_FRONTEND): CPPFLAGS += -DUSE_PRIVATE_ENCODING_FUNCS
+
+
 #
 # Shared library versions of object files
 #
diff --git a/src/common/meson.build b/src/common/meson.build
index 3b97497d1a..ae05ac63cf 100644
--- a/src/common/meson.build
+++ b/src/common/meson.build
@@ -112,8 +112,8 @@ common_sources_frontend_static += files(
   'logging.c',
 )

-# Build pgport once for backend, once for use in frontend binaries, and once
-# for use in shared libraries
+# Build pgcommon once for backend, once for use in frontend binaries, and
+# once for use in shared libraries
 #
 # XXX: in most environments we could probably link_whole pgcommon_shlib
 # against pgcommon_static, instead of compiling twice.
@@ -131,6 +131,9 @@ pgcommon_variants = {
   '': default_lib_args + {
     'sources': common_sources_frontend_static,
     'dependencies': [frontend_common_code],
+    # Files in libpgcommon.a should use/export the "xxx_private" versions
+    # of pg_char_to_encoding() and friends.
+    'c_args': ['-DUSE_PRIVATE_ENCODING_FUNCS'],
   },
   '_shlib': default_lib_args + {
     'pic': true,
diff --git a/src/include/mb/pg_wchar.h b/src/include/mb/pg_wchar.h
index 25276b199f..29cd5732f1 100644
--- a/src/include/mb/pg_wchar.h
+++ b/src/include/mb/pg_wchar.h
@@ -13,6 +13,9 @@
  *        included by libpq client programs.  In particular, a libpq client
  *        should not assume that the encoding IDs used by the version of libpq
  *        it's linked to match up with the IDs declared here.
+ *        To help prevent mistakes, relevant functions that are exported by
+ *        libpq have a physically different name when being referenced
+ *        statically.
  *
  *-------------------------------------------------------------------------
  */
@@ -562,6 +565,23 @@ surrogate_pair_to_codepoint(pg_wchar first, pg_wchar second)
 }


+/*
+ * The functions in this list are exported by libpq, and we need to be sure
+ * that we know which calls are satisfied by libpq and which are satisfied
+ * by static linkage to libpgcommon.  (This is because we might be using a
+ * libpq.so that's of a different major version and has encoding IDs that
+ * differ from the current version's.)  The nominal function names are what
+ * are actually used in and exported by libpq, while the names exported by
+ * libpgcommon.a and libpgcommon_srv.a end in "_private".
+ */
+#if defined(USE_PRIVATE_ENCODING_FUNCS) || !defined(FRONTEND)
+#define pg_char_to_encoding            pg_char_to_encoding_private
+#define pg_encoding_to_char            pg_encoding_to_char_private
+#define pg_valid_server_encoding    pg_valid_server_encoding_private
+#define pg_valid_server_encoding_id    pg_valid_server_encoding_id_private
+#define pg_utf_mblen                pg_utf_mblen_private
+#endif
+
 /*
  * These functions are considered part of libpq's exported API and
  * are also declared in libpq-fe.h.