Tsearch2 functionality migrates to core. The bulk of this work is by

Oleg Bartunov and Teodor Sigaev, but I did a lot of editorializing,
so anything that's broken is probably my fault.

Documentation is nonexistent as yet, but let's land the patch so we can
get some portability testing done.

src/backend/utils/adt/tsginidx.c

@@ -0,0 +1,157 @@
+/*-------------------------------------------------------------------------
+ *
+ * tsginidx.c
+ *	 GIN support functions for tsvector_ops
+ *
+ * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/tsginidx.c,v 1.1 2007/08/21 01:11:19 tgl Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/skey.h"
+#include "tsearch/ts_type.h"
+#include "tsearch/ts_utils.h"
+
+
+Datum
+gin_extract_tsvector(PG_FUNCTION_ARGS)
+{
+	TSVector	vector = PG_GETARG_TSVECTOR(0);
+	uint32	   *nentries = (uint32 *) PG_GETARG_POINTER(1);
+	Datum	   *entries = NULL;
+
+	*nentries = 0;
+	if (vector->size > 0)
+	{
+		int			i;
+		WordEntry  *we = ARRPTR(vector);
+
+		*nentries = (uint32) vector->size;
+		entries = (Datum *) palloc(sizeof(Datum) * vector->size);
+
+		for (i = 0; i < vector->size; i++)
+		{
+			text	   *txt = (text *) palloc(VARHDRSZ + we->len);
+
+			SET_VARSIZE(txt, VARHDRSZ + we->len);
+			memcpy(VARDATA(txt), STRPTR(vector) + we->pos, we->len);
+
+			entries[i] = PointerGetDatum(txt);
+
+			we++;
+		}
+	}
+
+	PG_FREE_IF_COPY(vector, 0);
+	PG_RETURN_POINTER(entries);
+}
+
+Datum
+gin_extract_query(PG_FUNCTION_ARGS)
+{
+	TSQuery		query = PG_GETARG_TSQUERY(0);
+	uint32	   *nentries = (uint32 *) PG_GETARG_POINTER(1);
+	StrategyNumber strategy = PG_GETARG_UINT16(2);
+	Datum	   *entries = NULL;
+
+	*nentries = 0;
+
+	if (query->size > 0)
+	{
+		int4		i,
+					j = 0,
+					len;
+		QueryItem  *item;
+
+		item = clean_NOT(GETQUERY(query), &len);
+		if (!item)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("query requires full scan, which is not supported by GIN indexes")));
+
+		item = GETQUERY(query);
+
+		for (i = 0; i < query->size; i++)
+			if (item[i].type == VAL)
+				(*nentries)++;
+
+		entries = (Datum *) palloc(sizeof(Datum) * (*nentries));
+
+		for (i = 0; i < query->size; i++)
+			if (item[i].type == VAL)
+			{
+				text	   *txt;
+
+				txt = (text *) palloc(VARHDRSZ + item[i].length);
+
+				SET_VARSIZE(txt, VARHDRSZ + item[i].length);
+				memcpy(VARDATA(txt), GETOPERAND(query) + item[i].distance, item[i].length);
+
+				entries[j++] = PointerGetDatum(txt);
+
+				if (strategy != TSearchWithClassStrategyNumber && item[i].weight != 0)
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							 errmsg("@@ operator does not support lexeme class restrictions"),
+							 errhint("Use the @@@ operator instead.")));
+			}
+	}
+	else
+		*nentries = -1;			/* nothing can be found */
+
+	PG_FREE_IF_COPY(query, 0);
+
+	PG_RETURN_POINTER(entries);
+}
+
+typedef struct
+{
+	QueryItem  *frst;
+	bool	   *mapped_check;
+} GinChkVal;
+
+static bool
+checkcondition_gin(void *checkval, QueryItem * val)
+{
+	GinChkVal  *gcv = (GinChkVal *) checkval;
+
+	return gcv->mapped_check[val - gcv->frst];
+}
+
+Datum
+gin_ts_consistent(PG_FUNCTION_ARGS)
+{
+	bool	   *check = (bool *) PG_GETARG_POINTER(0);
+	/* StrategyNumber strategy = PG_GETARG_UINT16(1); */
+	TSQuery		query = PG_GETARG_TSQUERY(2);
+	bool		res = FALSE;
+
+	if (query->size > 0)
+	{
+		int4		i,
+					j = 0;
+		QueryItem  *item;
+		GinChkVal	gcv;
+
+		gcv.frst = item = GETQUERY(query);
+		gcv.mapped_check = (bool *) palloc(sizeof(bool) * query->size);
+
+		for (i = 0; i < query->size; i++)
+			if (item[i].type == VAL)
+				gcv.mapped_check[i] = check[j++];
+
+		res = TS_execute(
+						 GETQUERY(query),
+						 &gcv,
+						 true,
+						 checkcondition_gin
+			);
+	}
+
+	PG_RETURN_BOOL(res);
+}