Improve parsetree representation of special functions such as CURRENT_DATE.

We implement a dozen or so parameterless functions that the SQL standard
defines special syntax for.  Up to now, that was done by converting them
into more or less ad-hoc constructs such as "'now'::text::date".  That's
messy for multiple reasons: it exposes what should be implementation
details to users, and performance is worse than it needs to be in several
cases.  To improve matters, invent a new expression node type
SQLValueFunction that can represent any of these parameterless functions.

Bump catversion because this changes stored parsetrees for rules.

Discussion: <30058.1463091294@sss.pgh.pa.us>

1 files changed, 24 insertions, 3 deletions

diff --git a/src/backend/nodes/nodeFuncs.c b/src/backend/nodes/nodeFuncs.c
index cd391673511..399744193c0 100644
--- a/src/backend/nodes/nodeFuncs.c
+++ b/src/backend/nodes/nodeFuncs.c
@@ -218,6 +218,9 @@ exprType(const Node *expr)
 		case T_MinMaxExpr:
 			type = ((const MinMaxExpr *) expr)->minmaxtype;
 			break;
+		case T_SQLValueFunction:
+			type = ((const SQLValueFunction *) expr)->type;
+			break;
 		case T_XmlExpr:
 			if (((const XmlExpr *) expr)->op == IS_DOCUMENT)
 				type = BOOLOID;
@@ -479,6 +482,8 @@ exprTypmod(const Node *expr)
 				return typmod;
 			}
 			break;
+		case T_SQLValueFunction:
+			return ((const SQLValueFunction *) expr)->typmod;
 		case T_CoerceToDomain:
 			return ((const CoerceToDomain *) expr)->resulttypmod;
 		case T_CoerceToDomainValue:
@@ -718,6 +723,8 @@ expression_returns_set_walker(Node *node, void *context)
 		return false;
 	if (IsA(node, MinMaxExpr))
 		return false;
+	if (IsA(node, SQLValueFunction))
+		return false;
 	if (IsA(node, XmlExpr))
 		return false;
 
@@ -883,6 +890,9 @@ exprCollation(const Node *expr)
 		case T_MinMaxExpr:
 			coll = ((const MinMaxExpr *) expr)->minmaxcollid;
 			break;
+		case T_SQLValueFunction:
+			coll = InvalidOid;	/* all cases return non-collatable types */
+			break;
 		case T_XmlExpr:
 
 			/*
@@ -1091,6 +1101,9 @@ exprSetCollation(Node *expr, Oid collation)
 		case T_MinMaxExpr:
 			((MinMaxExpr *) expr)->minmaxcollid = collation;
 			break;
+		case T_SQLValueFunction:
+			Assert(!OidIsValid(collation));		/* no collatable results */
+			break;
 		case T_XmlExpr:
 			Assert((((XmlExpr *) expr)->op == IS_XMLSERIALIZE) ?
 				   (collation == DEFAULT_COLLATION_OID) :
@@ -1364,6 +1377,10 @@ exprLocation(const Node *expr)
 			/* GREATEST/LEAST keyword should always be the first thing */
 			loc = ((const MinMaxExpr *) expr)->location;
 			break;
+		case T_SQLValueFunction:
+			/* function keyword should always be the first thing */
+			loc = ((const SQLValueFunction *) expr)->location;
+			break;
 		case T_XmlExpr:
 			{
 				const XmlExpr *xexpr = (const XmlExpr *) expr;
@@ -1633,9 +1650,10 @@ set_sa_opfuncid(ScalarArrayOpExpr *opexpr)
  * for themselves, in case additional checks should be made, or because they
  * have special rules about which parts of the tree need to be visited.
  *
- * Note: we ignore MinMaxExpr, XmlExpr, and CoerceToDomain nodes, because they
- * do not contain SQL function OIDs.  However, they can invoke SQL-visible
- * functions, so callers should take thought about how to treat them.
+ * Note: we ignore MinMaxExpr, SQLValueFunction, XmlExpr, and CoerceToDomain
+ * nodes, because they do not contain SQL function OIDs.  However, they can
+ * invoke SQL-visible functions, so callers should take thought about how to
+ * treat them.
  */
 bool
 check_functions_in_node(Node *node, check_function_callback checker,
@@ -1859,6 +1877,7 @@ expression_tree_walker(Node *node,
 		case T_CaseTestExpr:
 		case T_SetToDefault:
 		case T_CurrentOfExpr:
+		case T_SQLValueFunction:
 		case T_RangeTblRef:
 		case T_SortGroupClause:
 			/* primitive node types with no expression subnodes */
@@ -2433,6 +2452,7 @@ expression_tree_mutator(Node *node,
 		case T_CaseTestExpr:
 		case T_SetToDefault:
 		case T_CurrentOfExpr:
+		case T_SQLValueFunction:
 		case T_RangeTblRef:
 		case T_SortGroupClause:
 			return (Node *) copyObject(node);
@@ -3197,6 +3217,7 @@ raw_expression_tree_walker(Node *node,
 	{
 		case T_SetToDefault:
 		case T_CurrentOfExpr:
+		case T_SQLValueFunction:
 		case T_Integer:
 		case T_Float:
 		case T_String: