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, 39 insertions, 0 deletions

diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index df2d27d77ca..65510b010ba 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -1051,6 +1051,45 @@ typedef struct MinMaxExpr
 } MinMaxExpr;
 
 /*
+ * SQLValueFunction - parameterless functions with special grammar productions
+ *
+ * The SQL standard categorizes some of these as <datetime value function>
+ * and others as <general value specification>.  We call 'em SQLValueFunctions
+ * for lack of a better term.  We store type and typmod of the result so that
+ * some code doesn't need to know each function individually, and because
+ * we would need to store typmod anyway for some of the datetime functions.
+ * Note that currently, all variants return non-collating datatypes, so we do
+ * not need a collation field; also, all these functions are stable.
+ */
+typedef enum SQLValueFunctionOp
+{
+	SVFOP_CURRENT_DATE,
+	SVFOP_CURRENT_TIME,
+	SVFOP_CURRENT_TIME_N,
+	SVFOP_CURRENT_TIMESTAMP,
+	SVFOP_CURRENT_TIMESTAMP_N,
+	SVFOP_LOCALTIME,
+	SVFOP_LOCALTIME_N,
+	SVFOP_LOCALTIMESTAMP,
+	SVFOP_LOCALTIMESTAMP_N,
+	SVFOP_CURRENT_ROLE,
+	SVFOP_CURRENT_USER,
+	SVFOP_USER,
+	SVFOP_SESSION_USER,
+	SVFOP_CURRENT_CATALOG,
+	SVFOP_CURRENT_SCHEMA
+} SQLValueFunctionOp;
+
+typedef struct SQLValueFunction
+{
+	Expr		xpr;
+	SQLValueFunctionOp op;		/* which function this is */
+	Oid			type;			/* result type/typmod */
+	int32		typmod;
+	int			location;		/* token location, or -1 if unknown */
+} SQLValueFunction;
+
+/*
  * XmlExpr - various SQL/XML functions requiring special grammar productions
  *
  * 'name' carries the "NAME foo" argument (already XML-escaped).