Create a new expression node type RelabelType, which exists solely to

represent the result of a binary-compatible type coercion.  At runtime
it just evaluates its argument --- but during type resolution, exprType
will pick up the output type of the RelabelType node instead of the type
of the argument.  This solves some longstanding problems with dropped
type coercions, an example being 'select now()::abstime::int4' which
used to produce date-formatted output, not an integer, because the
coercion to int4 was dropped on the floor.

src/backend/nodes/copyfuncs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/nodes/copyfuncs.c,v 1.106 2000/02/15 20:49:09 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/nodes/copyfuncs.c,v 1.107 2000/02/20 21:32:05 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -873,6 +873,26 @@ _copySubLink(SubLink *from)
 	return newnode;
 }
 
+/* ----------------
+ *		_copyRelabelType
+ * ----------------
+ */
+static RelabelType *
+_copyRelabelType(RelabelType *from)
+{
+	RelabelType    *newnode = makeNode(RelabelType);
+
+	/* ----------------
+	 *	copy remainder of node
+	 * ----------------
+	 */
+	Node_Copy(from, newnode, arg);
+	newnode->resulttype = from->resulttype;
+	newnode->resulttypmod = from->resulttypmod;
+
+	return newnode;
+}
+
 /* ----------------
  *		_copyCaseExpr
  * ----------------
@@ -1617,6 +1637,9 @@ copyObject(void *from)
 		case T_SubLink:
 			retval = _copySubLink(from);
 			break;
+		case T_RelabelType:
+			retval = _copyRelabelType(from);
+			break;
 		case T_CaseExpr:
 			retval = _copyCaseExpr(from);
 			break;

src/backend/nodes/equalfuncs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/nodes/equalfuncs.c,v 1.61 2000/02/15 20:49:09 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/nodes/equalfuncs.c,v 1.62 2000/02/20 21:32:05 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -262,6 +262,18 @@ _equalSubLink(SubLink *a, SubLink *b)
 	return true;
 }
 
+static bool
+_equalRelabelType(RelabelType *a, RelabelType *b)
+{
+	if (!equal(a->arg, b->arg))
+		return false;
+	if (a->resulttype != b->resulttype)
+		return false;
+	if (a->resulttypmod != b->resulttypmod)
+		return false;
+	return true;
+}
+
 static bool
 _equalArray(Array *a, Array *b)
 {
@@ -806,6 +818,9 @@ equal(void *a, void *b)
 		case T_SubLink:
 			retval = _equalSubLink(a, b);
 			break;
+		case T_RelabelType:
+			retval = _equalRelabelType(a, b);
+			break;
 		case T_Func:
 			retval = _equalFunc(a, b);
 			break;

src/backend/nodes/freefuncs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/nodes/Attic/freefuncs.c,v 1.36 2000/02/15 20:49:09 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/nodes/Attic/freefuncs.c,v 1.37 2000/02/20 21:32:05 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -650,6 +650,22 @@ _freeSubLink(SubLink *node)
 	pfree(node);
 }
 
+/* ----------------
+ *		_freeRelabelType
+ * ----------------
+ */
+static void
+_freeRelabelType(RelabelType *node)
+{
+	/* ----------------
+	 *	free remainder of node
+	 * ----------------
+	 */
+	freeObject(node->arg);
+
+	pfree(node);
+}
+
 /* ----------------
  *		_freeCaseExpr
  * ----------------
@@ -1241,6 +1257,9 @@ freeObject(void *node)
 		case T_SubLink:
 			_freeSubLink(node);
 			break;
+		case T_RelabelType:
+			_freeRelabelType(node);
+			break;
 		case T_CaseExpr:
 			_freeCaseExpr(node);
 			break;

src/backend/nodes/outfuncs.c

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2000, PostgreSQL, Inc
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	$Header: /cvsroot/pgsql/src/backend/nodes/outfuncs.c,v 1.108 2000/02/15 20:49:09 tgl Exp $
+ *	$Header: /cvsroot/pgsql/src/backend/nodes/outfuncs.c,v 1.109 2000/02/20 21:32:05 tgl Exp $
  *
  * NOTES
  *	  Every (plan) node in POSTGRES has an associated "out" routine which
@@ -770,6 +770,19 @@ _outSubLink(StringInfo str, SubLink *node)
 	_outNode(str, node->subselect);
 }
 
+/*
+ *	RelabelType
+ */
+static void
+_outRelabelType(StringInfo str, RelabelType *node)
+{
+	appendStringInfo(str, " RELABELTYPE :arg ");
+	_outNode(str, node->arg);
+
+	appendStringInfo(str, " :resulttype %u :resulttypmod %d ",
+					 node->resulttype, node->resulttypmod);
+}
+
 /*
  *	Array is a subclass of Expr
  */
@@ -1496,6 +1509,9 @@ _outNode(StringInfo str, void *obj)
 			case T_SubLink:
 				_outSubLink(str, obj);
 				break;
+			case T_RelabelType:
+				_outRelabelType(str, obj);
+				break;
 			case T_Array:
 				_outArray(str, obj);
 				break;

src/backend/nodes/readfuncs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/nodes/readfuncs.c,v 1.84 2000/02/15 20:49:12 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/nodes/readfuncs.c,v 1.85 2000/02/20 21:32:05 tgl Exp $
  *
  * NOTES
  *	  Most of the read functions for plan nodes are tested. (In fact, they
@@ -1191,6 +1191,35 @@ _readSubLink()
 	return local_node;
 }
 
+/* ----------------
+ *		_readRelabelType
+ *
+ *	RelabelType is a subclass of Node
+ * ----------------
+ */
+static RelabelType *
+_readRelabelType()
+{
+	RelabelType *local_node;
+	char	   *token;
+	int			length;
+
+	local_node = makeNode(RelabelType);
+
+	token = lsptok(NULL, &length);		/* eat :arg */
+	local_node->arg = nodeRead(true);	/* now read it */
+
+	token = lsptok(NULL, &length);		/* eat :resulttype */
+	token = lsptok(NULL, &length);		/* get resulttype */
+	local_node->resulttype = (Oid) atol(token);
+
+	token = lsptok(NULL, &length);		/* eat :resulttypmod */
+	token = lsptok(NULL, &length);		/* get resulttypmod */
+	local_node->resulttypmod = atoi(token);
+
+	return local_node;
+}
+
 /*
  *	Stuff from execnodes.h
  */
@@ -1820,6 +1849,8 @@ parsePlanString(void)
 		return_value = _readAggref();
 	else if (length == 7 && strncmp(token, "SUBLINK", length) == 0)
 		return_value = _readSubLink();
+	else if (length == 11 && strncmp(token, "RELABELTYPE", length) == 0)
+		return_value = _readRelabelType();
 	else if (length == 3 && strncmp(token, "AGG", length) == 0)
 		return_value = _readAgg();
 	else if (length == 4 && strncmp(token, "HASH", length) == 0)