Convert contrib/hstore_plpython to not use direct linking to other modules.

Previously, on most platforms, we allowed hstore_plpython's references
to hstore and plpython to be unresolved symbols at link time, trusting
the dynamic linker to resolve them when the module is loaded.  This
has a number of problems, the worst being that the dynamic linker
does not know where the references come from and can do nothing but
fail if those other modules haven't been loaded.  We've more or less
gotten away with that for the limited use-case of datatype transform
modules, but even there, it requires some awkward hacks, most recently
commit 83c249200.

Instead, let's not treat these references as linker-resolvable at all,
but use function pointers that are manually filled in by the module's
_PG_init function.  There are few enough contact points that this
doesn't seem unmaintainable, at least for these use-cases.  (Note that
the same technique wouldn't work at all for decoupling from libpython
itself, but fortunately that's just a standard shared library and can
be linked to normally.)

This is an initial patch that just converts hstore_plpython.  If the
buildfarm doesn't find any fatal problems, I'll work on the other
transform modules soon.

Tom Lane, per an idea of Andres Freund's.

Discussion: <2652.1475512158@sss.pgh.pa.us>

contrib/hstore_plpython/Makefile

@@ -4,7 +4,7 @@ MODULE_big = hstore_plpython$(python_majorversion)
 OBJS = hstore_plpython.o $(WIN32RES)
 PGFILEDESC = "hstore_plpython - hstore transform for plpython"
 
-PG_CPPFLAGS = -I$(top_srcdir)/src/pl/plpython $(python_includespec) -I$(top_srcdir)/contrib/hstore
+PG_CPPFLAGS = -I$(top_srcdir)/src/pl/plpython $(python_includespec) -I$(top_srcdir)/contrib/hstore -DPLPYTHON_LIBNAME='"plpython$(python_majorversion)"'
 
 EXTENSION = hstore_plpythonu hstore_plpython2u hstore_plpython3u
 DATA = hstore_plpythonu--1.0.sql hstore_plpython2u--1.0.sql hstore_plpython3u--1.0.sql
@@ -23,19 +23,18 @@ include $(top_builddir)/src/Makefile.global
 include $(top_srcdir)/contrib/contrib-global.mk
 endif
 
-# In configurations that forbid undefined symbols in libraries, link with each
-# dependency.  This does preclude pgxs builds.
+# We must link libpython explicitly
 ifeq ($(PORTNAME), aix)
 rpathdir = $(pkglibdir):$(python_libdir)
-SHLIB_LINK += ../hstore/libhstore.exp $(python_libspec) $(python_additional_libs) $(sort $(wildcard ../../src/pl/plpython/libplpython*.exp))
-endif
+SHLIB_LINK += $(python_libspec) $(python_additional_libs)
+else
 ifeq ($(PORTNAME), win32)
-SHLIB_LINK += ../hstore/libhstore.a $(sort $(wildcard ../../src/pl/plpython/libpython*.a)) $(sort $(wildcard ../../src/pl/plpython/libplpython*.a))
+# ... see silliness in plpython Makefile ...
+SHLIB_LINK += $(sort $(wildcard ../../src/pl/plpython/libpython*.a))
+else
+rpathdir = $(python_libdir)
+SHLIB_LINK += $(python_libspec)
 endif
-
-ifeq ($(PORTNAME), cygwin)
-SHLIB_LINK += -L../hstore -lhstore -L../../src/pl/plpython \
-	-lplpython$(python_majorversion) $(python_libspec)
 endif
 
 REGRESS_OPTS += --load-extension=hstore

contrib/hstore_plpython/hstore_plpython.c

@@ -1,4 +1,5 @@
 #include "postgres.h"
+
 #include "fmgr.h"
 #include "plpython.h"
 #include "plpy_typeio.h"
@@ -6,6 +7,70 @@
 
 PG_MODULE_MAGIC;
 
+extern void _PG_init(void);
+
+/* Linkage to functions in plpython module */
+typedef char *(*PLyObject_AsString_t) (PyObject *plrv);
+
+static PLyObject_AsString_t PLyObject_AsString_p;
+
+/* Linkage to functions in hstore module */
+typedef HStore *(*hstoreUpgrade_t) (Datum orig);
+typedef int (*hstoreUniquePairs_t) (Pairs *a, int32 l, int32 *buflen);
+typedef HStore *(*hstorePairs_t) (Pairs *pairs, int32 pcount, int32 buflen);
+typedef size_t (*hstoreCheckKeyLen_t) (size_t len);
+typedef size_t (*hstoreCheckValLen_t) (size_t len);
+
+static hstoreUpgrade_t hstoreUpgrade_p;
+static hstoreUniquePairs_t hstoreUniquePairs_p;
+static hstorePairs_t hstorePairs_p;
+static hstoreCheckKeyLen_t hstoreCheckKeyLen_p;
+static hstoreCheckValLen_t hstoreCheckValLen_p;
+
+
+/*
+ * Module initialize function: fetch function pointers for cross-module calls.
+ */
+void
+_PG_init(void)
+{
+	/* These asserts verify that typedefs above match original declarations */
+	AssertVariableIsOfType(&PLyObject_AsString, PLyObject_AsString_t);
+	AssertVariableIsOfType(&hstoreUpgrade, hstoreUpgrade_t);
+	AssertVariableIsOfType(&hstoreUniquePairs, hstoreUniquePairs_t);
+	AssertVariableIsOfType(&hstorePairs, hstorePairs_t);
+	AssertVariableIsOfType(&hstoreCheckKeyLen, hstoreCheckKeyLen_t);
+	AssertVariableIsOfType(&hstoreCheckValLen, hstoreCheckValLen_t);
+
+	PLyObject_AsString_p = (PLyObject_AsString_t)
+		load_external_function("$libdir/" PLPYTHON_LIBNAME, "PLyObject_AsString",
+							   true, NULL);
+	hstoreUpgrade_p = (hstoreUpgrade_t)
+		load_external_function("$libdir/hstore", "hstoreUpgrade",
+							   true, NULL);
+	hstoreUniquePairs_p = (hstoreUniquePairs_t)
+		load_external_function("$libdir/hstore", "hstoreUniquePairs",
+							   true, NULL);
+	hstorePairs_p = (hstorePairs_t)
+		load_external_function("$libdir/hstore", "hstorePairs",
+							   true, NULL);
+	hstoreCheckKeyLen_p = (hstoreCheckKeyLen_t)
+		load_external_function("$libdir/hstore", "hstoreCheckKeyLen",
+							   true, NULL);
+	hstoreCheckValLen_p = (hstoreCheckValLen_t)
+		load_external_function("$libdir/hstore", "hstoreCheckValLen",
+							   true, NULL);
+}
+
+
+/* These defines must be after the module init function */
+#define PLyObject_AsString PLyObject_AsString_p
+#define hstoreUpgrade hstoreUpgrade_p
+#define hstoreUniquePairs hstoreUniquePairs_p
+#define hstorePairs hstorePairs_p
+#define hstoreCheckKeyLen hstoreCheckKeyLen_p
+#define hstoreCheckValLen hstoreCheckValLen_p
+
 
 PG_FUNCTION_INFO_V1(hstore_to_plpython);
 

contrib/hstore_plpython/hstore_plpython2u--1.0.sql

@@ -3,11 +3,6 @@
 -- complain if script is sourced in psql, rather than via CREATE EXTENSION
 \echo Use "CREATE EXTENSION hstore_plpython2u" to load this file. \quit
 
--- make sure the prerequisite libraries are loaded
-LOAD 'plpython2';
-SELECT NULL::hstore;
-
-
 CREATE FUNCTION hstore_to_plpython2(val internal) RETURNS internal
 LANGUAGE C STRICT IMMUTABLE
 AS 'MODULE_PATHNAME', 'hstore_to_plpython';

contrib/hstore_plpython/hstore_plpython3u--1.0.sql

@@ -3,11 +3,6 @@
 -- complain if script is sourced in psql, rather than via CREATE EXTENSION
 \echo Use "CREATE EXTENSION hstore_plpython3u" to load this file. \quit
 
--- make sure the prerequisite libraries are loaded
-LOAD 'plpython3';
-SELECT NULL::hstore;
-
-
 CREATE FUNCTION hstore_to_plpython3(val internal) RETURNS internal
 LANGUAGE C STRICT IMMUTABLE
 AS 'MODULE_PATHNAME', 'hstore_to_plpython';

contrib/hstore_plpython/hstore_plpythonu--1.0.sql

@@ -3,11 +3,6 @@
 -- complain if script is sourced in psql, rather than via CREATE EXTENSION
 \echo Use "CREATE EXTENSION hstore_plpythonu" to load this file. \quit
 
--- make sure the prerequisite libraries are loaded
-LOAD 'plpython2';  -- change to plpython3 if that ever becomes the default
-SELECT NULL::hstore;
-
-
 CREATE FUNCTION hstore_to_plpython(val internal) RETURNS internal
 LANGUAGE C STRICT IMMUTABLE
 AS 'MODULE_PATHNAME';

src/tools/msvc/Mkvcbuild.pm

@@ -475,10 +475,11 @@ sub mkvcbuild
 		$plpython->AddReference($postgres);
 
 		# Add transform modules dependent on plpython
-		AddTransformModule(
+		my $hstore_plpython = AddTransformModule(
 			'hstore_plpython' . $pymajorver, 'contrib/hstore_plpython',
 			'plpython' . $pymajorver,        'src/pl/plpython',
 			'hstore',                        'contrib/hstore');
+		$hstore_plpython->AddDefine('PLPYTHON_LIBNAME="plpython' . $pymajorver . '"');
 		AddTransformModule(
 			'ltree_plpython' . $pymajorver, 'contrib/ltree_plpython',
 			'plpython' . $pymajorver,       'src/pl/plpython',