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.

1 files changed, 44 insertions, 1 deletions

diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 664a0dfaaa5..4bb84f15214 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.59 2000/02/15 03:37:36 thomas Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.60 2000/02/20 21:32:06 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -1150,6 +1150,37 @@ eval_const_expressions_mutator (Node *node, void *context)
         newexpr->args = args;
         return (Node *) newexpr;
 	}
+	if (IsA(node, RelabelType))
+	{
+		/*
+		 * If we can simplify the input to a constant, then we don't need
+		 * the RelabelType node anymore: just change the type field of
+		 * the Const node.  Otherwise keep the RelabelType node.
+		 *
+		 * XXX if relabel has a nondefault resulttypmod, do we need to
+		 * keep it to show that?  At present I don't think so.
+		 */
+		RelabelType *relabel = (RelabelType *) node;
+		Node	   *arg;
+
+		arg = eval_const_expressions_mutator(relabel->arg, context);
+		if (arg && IsA(arg, Const))
+		{
+			Const  *con = (Const *) arg;
+
+			con->consttype = relabel->resulttype;
+			return (Node *) con;
+		}
+		else
+		{
+			RelabelType *newrelabel = makeNode(RelabelType);
+
+			newrelabel->arg = arg;
+			newrelabel->resulttype = relabel->resulttype;
+			newrelabel->resulttypmod = relabel->resulttypmod;
+			return (Node *) newrelabel;
+		}
+	}
 	if (IsA(node, CaseExpr))
 	{
 		/*
@@ -1392,6 +1423,8 @@ expression_tree_walker(Node *node, bool (*walker) (), void *context)
 					return true;
 			}
 			break;
+		case T_RelabelType:
+			return walker(((RelabelType *) node)->arg, context);
 		case T_CaseExpr:
 			{
 				CaseExpr   *caseexpr = (CaseExpr *) node;
@@ -1603,6 +1636,16 @@ expression_tree_mutator(Node *node, Node * (*mutator) (), void *context)
 				return (Node *) newnode;
 			}
 			break;
+		case T_RelabelType:
+			{
+				RelabelType *relabel = (RelabelType *) node;
+				RelabelType *newnode;
+
+				FLATCOPY(newnode, relabel, RelabelType);
+				MUTATE(newnode->arg, relabel->arg, Node *);
+				return (Node *) newnode;
+			}
+			break;
 		case T_CaseExpr:
 			{
 				CaseExpr   *caseexpr = (CaseExpr *) node;