Prevent failure when RowExpr or XmlExpr is parse-analyzed twice.

transformExpr() is required to cope with already-transformed expression
trees, for various ugly-but-not-quite-worth-cleaning-up reasons.  However,
some of its newer subroutines hadn't gotten the memo.  This accounts for
bug #7763 from Norbert Buchmuller: transformRowExpr() was overwriting the
previously determined type of a RowExpr during CREATE TABLE LIKE INCLUDING
INDEXES.  Additional investigation showed that transformXmlExpr had the
same kind of problem, but all the other cases seem to be safe.

Andres Freund and Tom Lane

src/backend/parser/gram.y

@@ -13341,6 +13341,7 @@ makeXmlExpr(XmlExprOp op, char *name, List *named_args, List *args,
 	x->args = args;
 	/* xmloption, if relevant, must be filled in by caller */
 	/* type and typmod will be filled in during parse analysis */
+	x->type = InvalidOid;			/* marks the node as not analyzed */
 	x->location = location;
 	return (Node *) x;
 }

src/backend/parser/parse_expr.c

@@ -92,6 +92,8 @@ static Expr *make_distinct_op(ParseState *pstate, List *opname,
  *	function argument to the required type (via coerce_type())
  *	can apply transformExpr to an already-transformed subexpression.
  *	An example here is "SELECT count(*) + 1.0 FROM table".
+ *	3. CREATE TABLE t1 (LIKE t2 INCLUDING INDEXES) can pass in
+ *	already-transformed index expressions.
  * While it might be possible to eliminate these cases, the path of
  * least resistance so far has been to ensure that transformExpr() does
  * no damage if applied to an already-transformed tree.  This is pretty
@@ -1775,11 +1777,17 @@ transformArrayExpr(ParseState *pstate, A_ArrayExpr *a,
 static Node *
 transformRowExpr(ParseState *pstate, RowExpr *r)
 {
-	RowExpr    *newr = makeNode(RowExpr);
+	RowExpr    *newr;
 	char		fname[16];
 	int			fnum;
 	ListCell   *lc;
 
+	/* If we already transformed this node, do nothing */
+	if (OidIsValid(r->row_typeid))
+		return (Node *) r;
+
+	newr = makeNode(RowExpr);
+
 	/* Transform the field expressions */
 	newr->args = transformExpressionList(pstate, r->args, pstate->p_expr_kind);
 
@@ -1880,16 +1888,23 @@ transformMinMaxExpr(ParseState *pstate, MinMaxExpr *m)
 static Node *
 transformXmlExpr(ParseState *pstate, XmlExpr *x)
 {
-	XmlExpr    *newx = makeNode(XmlExpr);
+	XmlExpr    *newx;
 	ListCell   *lc;
 	int			i;
 
+	/* If we already transformed this node, do nothing */
+	if (OidIsValid(x->type))
+		return (Node *) x;
+
+	newx = makeNode(XmlExpr);
 	newx->op = x->op;
 	if (x->name)
 		newx->name = map_sql_identifier_to_xml_name(x->name, false, false);
 	else
 		newx->name = NULL;
 	newx->xmloption = x->xmloption;
+	newx->type = XMLOID;		/* this just marks the node as transformed */
+	newx->typmod = -1;
 	newx->location = x->location;
 
 	/*

src/include/nodes/primnodes.h

@@ -958,7 +958,8 @@ typedef struct MinMaxExpr
  *
  * Note: result type/typmod/collation are not stored, but can be deduced
  * from the XmlExprOp.	The type/typmod fields are just used for display
- * purposes, and are NOT the true result type of the node.
+ * purposes, and are NOT necessarily the true result type of the node.
+ * (We also use type == InvalidOid to mark a not-yet-parse-analyzed XmlExpr.)
  */
 typedef enum XmlExprOp
 {