Add transforms feature

This provides a mechanism for specifying conversions between SQL data
types and procedural languages.  As examples, there are transforms
for hstore and ltree for PL/Perl and PL/Python.

reviews by Pavel Stěhule and Andres Freund

contrib/ltree_plpython/.gitignore

@@ -0,0 +1,6 @@
+# Generated subdirectories
+/expected/python3/
+/log/
+/results/
+/sql/python3/
+/tmp_check/

contrib/ltree_plpython/Makefile

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+# contrib/ltree_plpython/Makefile
+
+MODULE_big = ltree_plpython$(python_majorversion)
+OBJS = ltree_plpython.o
+
+PG_CPPFLAGS = -I$(top_srcdir)/src/pl/plpython $(python_includespec) -I$(top_srcdir)/contrib/ltree
+
+EXTENSION = ltree_plpythonu ltree_plpython2u ltree_plpython3u
+DATA = ltree_plpythonu--1.0.sql ltree_plpython2u--1.0.sql ltree_plpython3u--1.0.sql
+
+REGRESS = ltree_plpython
+REGRESS_PLPYTHON3_MANGLE := $(REGRESS)
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = contrib/ltree_plpython
+top_builddir = ../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif
+
+REGRESS_OPTS = --load-extension=ltree
+ifeq ($(python_majorversion),2)
+REGRESS_OPTS += --load-extension=plpythonu --load-extension=ltree_plpythonu
+endif
+EXTRA_INSTALL = contrib/ltree
+
+include $(top_srcdir)/src/pl/plpython/regress-python3-mangle.mk

contrib/ltree_plpython/expected/ltree_plpython.out

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+CREATE EXTENSION plpython2u;
+CREATE EXTENSION ltree_plpython2u;
+CREATE FUNCTION test1(val ltree) RETURNS int
+LANGUAGE plpythonu
+TRANSFORM FOR TYPE ltree
+AS $$
+plpy.info(repr(val))
+return len(val)
+$$;
+SELECT test1('aa.bb.cc'::ltree);
+INFO:  ['aa', 'bb', 'cc']
+CONTEXT:  PL/Python function "test1"
+ test1 
+-------
+     3
+(1 row)
+
+CREATE FUNCTION test1n(val ltree) RETURNS int
+LANGUAGE plpython2u
+TRANSFORM FOR TYPE ltree
+AS $$
+plpy.info(repr(val))
+return len(val)
+$$;
+SELECT test1n('aa.bb.cc'::ltree);
+INFO:  ['aa', 'bb', 'cc']
+CONTEXT:  PL/Python function "test1n"
+ test1n 
+--------
+      3
+(1 row)
+
+CREATE FUNCTION test2() RETURNS ltree
+LANGUAGE plpythonu
+TRANSFORM FOR TYPE ltree
+AS $$
+return ['foo', 'bar', 'baz']
+$$;
+-- plpython to ltree is not yet implemented, so this will fail,
+-- because it will try to parse the Python list as an ltree input
+-- string.
+SELECT test2();
+ERROR:  syntax error at position 0
+CONTEXT:  while creating return value
+PL/Python function "test2"

contrib/ltree_plpython/ltree_plpython.c

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+#include "postgres.h"
+#include "fmgr.h"
+#include "plpython.h"
+#include "ltree.h"
+
+PG_MODULE_MAGIC;
+
+
+PG_FUNCTION_INFO_V1(ltree_to_plpython);
+Datum ltree_to_plpython(PG_FUNCTION_ARGS);
+
+Datum
+ltree_to_plpython(PG_FUNCTION_ARGS)
+{
+	ltree	   *in = PG_GETARG_LTREE(0);
+	int			i;
+	PyObject   *list;
+	ltree_level *curlevel;
+
+	list = PyList_New(in->numlevel);
+
+	curlevel = LTREE_FIRST(in);
+	for (i = 0; i < in->numlevel; i++)
+	{
+		PyList_SetItem(list, i, PyString_FromStringAndSize(curlevel->name, curlevel->len));
+		curlevel = LEVEL_NEXT(curlevel);
+	}
+
+	PG_FREE_IF_COPY(in, 0);
+
+	return PointerGetDatum(list);
+}

contrib/ltree_plpython/ltree_plpython2u--1.0.sql

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+-- make sure the prerequisite libraries are loaded
+DO '1' LANGUAGE plpython2u;
+SELECT NULL::ltree;
+
+
+CREATE FUNCTION ltree_to_plpython2(val internal) RETURNS internal
+LANGUAGE C STRICT IMMUTABLE
+AS 'MODULE_PATHNAME', 'ltree_to_plpython';
+
+CREATE TRANSFORM FOR ltree LANGUAGE plpython2u (
+    FROM SQL WITH FUNCTION ltree_to_plpython2(internal)
+);

contrib/ltree_plpython/ltree_plpython2u.control

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+# ltree_plpython2u extension
+comment = 'transform between ltree and plpython2u'
+default_version = '1.0'
+module_pathname = '$libdir/ltree_plpython2'
+relocatable = true
+requires = 'ltree,plpython2u'

contrib/ltree_plpython/ltree_plpython3u--1.0.sql

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+-- make sure the prerequisite libraries are loaded
+DO '1' LANGUAGE plpython3u;
+SELECT NULL::ltree;
+
+
+CREATE FUNCTION ltree_to_plpython3(val internal) RETURNS internal
+LANGUAGE C STRICT IMMUTABLE
+AS 'MODULE_PATHNAME', 'ltree_to_plpython';
+
+CREATE TRANSFORM FOR ltree LANGUAGE plpython3u (
+    FROM SQL WITH FUNCTION ltree_to_plpython3(internal)
+);

contrib/ltree_plpython/ltree_plpython3u.control

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+# ltree_plpython3u extension
+comment = 'transform between ltree and plpython3u'
+default_version = '1.0'
+module_pathname = '$libdir/ltree_plpython3'
+relocatable = true
+requires = 'ltree,plpython3u'

contrib/ltree_plpython/ltree_plpythonu--1.0.sql

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+-- make sure the prerequisite libraries are loaded
+DO '1' LANGUAGE plpythonu;
+SELECT NULL::ltree;
+
+
+CREATE FUNCTION ltree_to_plpython(val internal) RETURNS internal
+LANGUAGE C STRICT IMMUTABLE
+AS 'MODULE_PATHNAME';
+
+CREATE TRANSFORM FOR ltree LANGUAGE plpythonu (
+    FROM SQL WITH FUNCTION ltree_to_plpython(internal)
+);

contrib/ltree_plpython/ltree_plpythonu.control

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+# ltree_plpythonu extension
+comment = 'transform between ltree and plpythonu'
+default_version = '1.0'
+module_pathname = '$libdir/ltree_plpython2'
+relocatable = true
+requires = 'ltree,plpythonu'

contrib/ltree_plpython/sql/ltree_plpython.sql

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+CREATE EXTENSION plpython2u;
+CREATE EXTENSION ltree_plpython2u;
+
+
+CREATE FUNCTION test1(val ltree) RETURNS int
+LANGUAGE plpythonu
+TRANSFORM FOR TYPE ltree
+AS $$
+plpy.info(repr(val))
+return len(val)
+$$;
+
+SELECT test1('aa.bb.cc'::ltree);
+
+
+CREATE FUNCTION test1n(val ltree) RETURNS int
+LANGUAGE plpython2u
+TRANSFORM FOR TYPE ltree
+AS $$
+plpy.info(repr(val))
+return len(val)
+$$;
+
+SELECT test1n('aa.bb.cc'::ltree);
+
+
+CREATE FUNCTION test2() RETURNS ltree
+LANGUAGE plpythonu
+TRANSFORM FOR TYPE ltree
+AS $$
+return ['foo', 'bar', 'baz']
+$$;
+
+-- plpython to ltree is not yet implemented, so this will fail,
+-- because it will try to parse the Python list as an ltree input
+-- string.
+SELECT test2();