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/tsquery_cleanup.c

@@ -0,0 +1,261 @@
+/*-------------------------------------------------------------------------
+ *
+ * tsquery_cleanup.c
+ *	 Cleanup query from NOT values and/or stopword
+ *	 Utility functions to correct work.
+ *
+ * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/tsquery_cleanup.c,v 1.1 2007/08/21 01:11:19 tgl Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "tsearch/ts_type.h"
+#include "tsearch/ts_utils.h"
+
+typedef struct NODE
+{
+	struct NODE *left;
+	struct NODE *right;
+	QueryItem  *valnode;
+} NODE;
+
+/*
+ * make query tree from plain view of query
+ */
+static NODE *
+maketree(QueryItem * in)
+{
+	NODE	   *node = (NODE *) palloc(sizeof(NODE));
+
+	node->valnode = in;
+	node->right = node->left = NULL;
+	if (in->type == OPR)
+	{
+		node->right = maketree(in + 1);
+		if (in->val != (int4) '!')
+			node->left = maketree(in + in->left);
+	}
+	return node;
+}
+
+typedef struct
+{
+	QueryItem  *ptr;
+	int4		len;
+	int4		cur;
+} PLAINTREE;
+
+static void
+plainnode(PLAINTREE * state, NODE * node)
+{
+	if (state->cur == state->len)
+	{
+		state->len *= 2;
+		state->ptr = (QueryItem *) repalloc((void *) state->ptr, state->len * sizeof(QueryItem));
+	}
+	memcpy((void *) &(state->ptr[state->cur]), (void *) node->valnode, sizeof(QueryItem));
+	if (node->valnode->type == VAL)
+		state->cur++;
+	else if (node->valnode->val == (int4) '!')
+	{
+		state->ptr[state->cur].left = 1;
+		state->cur++;
+		plainnode(state, node->right);
+	}
+	else
+	{
+		int4		cur = state->cur;
+
+		state->cur++;
+		plainnode(state, node->right);
+		state->ptr[cur].left = state->cur - cur;
+		plainnode(state, node->left);
+	}
+	pfree(node);
+}
+
+/*
+ * make plain view of tree from 'normal' view of tree
+ */
+static QueryItem *
+plaintree(NODE * root, int4 *len)
+{
+	PLAINTREE	pl;
+
+	pl.cur = 0;
+	pl.len = 16;
+	if (root && (root->valnode->type == VAL || root->valnode->type == OPR))
+	{
+		pl.ptr = (QueryItem *) palloc(pl.len * sizeof(QueryItem));
+		plainnode(&pl, root);
+	}
+	else
+		pl.ptr = NULL;
+	*len = pl.cur;
+	return pl.ptr;
+}
+
+static void
+freetree(NODE * node)
+{
+	if (!node)
+		return;
+	if (node->left)
+		freetree(node->left);
+	if (node->right)
+		freetree(node->right);
+	pfree(node);
+}
+
+/*
+ * clean tree for ! operator.
+ * It's usefull for debug, but in
+ * other case, such view is used with search in index.
+ * Operator ! always return TRUE
+ */
+static NODE *
+clean_NOT_intree(NODE * node)
+{
+	if (node->valnode->type == VAL)
+		return node;
+
+	if (node->valnode->val == (int4) '!')
+	{
+		freetree(node);
+		return NULL;
+	}
+
+	/* operator & or | */
+	if (node->valnode->val == (int4) '|')
+	{
+		if ((node->left = clean_NOT_intree(node->left)) == NULL ||
+			(node->right = clean_NOT_intree(node->right)) == NULL)
+		{
+			freetree(node);
+			return NULL;
+		}
+	}
+	else
+	{
+		NODE	   *res = node;
+
+		node->left = clean_NOT_intree(node->left);
+		node->right = clean_NOT_intree(node->right);
+		if (node->left == NULL && node->right == NULL)
+		{
+			pfree(node);
+			res = NULL;
+		}
+		else if (node->left == NULL)
+		{
+			res = node->right;
+			pfree(node);
+		}
+		else if (node->right == NULL)
+		{
+			res = node->left;
+			pfree(node);
+		}
+		return res;
+	}
+	return node;
+}
+
+QueryItem *
+clean_NOT(QueryItem * ptr, int4 *len)
+{
+	NODE	   *root = maketree(ptr);
+
+	return plaintree(clean_NOT_intree(root), len);
+}
+
+
+#ifdef V_UNKNOWN				/* exists in Windows headers */
+#undef V_UNKNOWN
+#endif
+
+#define V_UNKNOWN	0
+#define V_TRUE		1
+#define V_FALSE		2
+#define V_STOP		3
+
+/*
+ * Clean query tree from values which is always in
+ * text (stopword)
+ */
+static NODE *
+clean_fakeval_intree(NODE * node, char *result)
+{
+	char		lresult = V_UNKNOWN,
+				rresult = V_UNKNOWN;
+
+	if (node->valnode->type == VAL)
+		return node;
+	else if (node->valnode->type == VALSTOP)
+	{
+		pfree(node);
+		*result = V_STOP;
+		return NULL;
+	}
+
+
+	if (node->valnode->val == (int4) '!')
+	{
+		node->right = clean_fakeval_intree(node->right, &rresult);
+		if (!node->right)
+		{
+			*result = V_STOP;
+			freetree(node);
+			return NULL;
+		}
+	}
+	else
+	{
+		NODE	   *res = node;
+
+		node->left = clean_fakeval_intree(node->left, &lresult);
+		node->right = clean_fakeval_intree(node->right, &rresult);
+		if (lresult == V_STOP && rresult == V_STOP)
+		{
+			freetree(node);
+			*result = V_STOP;
+			return NULL;
+		}
+		else if (lresult == V_STOP)
+		{
+			res = node->right;
+			pfree(node);
+		}
+		else if (rresult == V_STOP)
+		{
+			res = node->left;
+			pfree(node);
+		}
+		return res;
+	}
+	return node;
+}
+
+QueryItem *
+clean_fakeval(QueryItem * ptr, int4 *len)
+{
+	NODE	   *root = maketree(ptr);
+	char		result = V_UNKNOWN;
+	NODE	   *resroot;
+
+	resroot = clean_fakeval_intree(root, &result);
+	if (result != V_UNKNOWN)
+	{
+		elog(NOTICE, "query contains only stopword(s) or doesn't contain lexeme(s), ignored");
+		*len = 0;
+		return NULL;
+	}
+
+	return plaintree(resroot, len);
+}