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>

3 files changed, 134 insertions, 95 deletions

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 6a0f7b393cb..cb5cfc480cf 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -165,6 +165,8 @@ static Node *makeAndExpr(Node *lexpr, Node *rexpr, int location);
 static Node *makeOrExpr(Node *lexpr, Node *rexpr, int location);
 static Node *makeNotExpr(Node *expr, int location);
 static Node *makeAArrayExpr(List *elements, int location);
+static Node *makeSQLValueFunction(SQLValueFunctionOp op, int32 typmod,
+								  int location);
 static Node *makeXmlExpr(XmlExprOp op, char *name, List *named_args,
 						 List *args, int location);
 static List *mergeTableFuncParameters(List *func_args, List *columns);
@@ -12330,143 +12332,63 @@ func_expr_common_subexpr:
 				}
 			| CURRENT_DATE
 				{
-					/*
-					 * Translate as "'now'::text::date".
-					 *
-					 * We cannot use "'now'::date" because coerce_type() will
-					 * immediately reduce that to a constant representing
-					 * today's date.  We need to delay the conversion until
-					 * runtime, else the wrong things will happen when
-					 * CURRENT_DATE is used in a column default value or rule.
-					 *
-					 * This could be simplified if we had a way to generate
-					 * an expression tree representing runtime application
-					 * of type-input conversion functions.  (As of PG 7.3
-					 * that is actually possible, but not clear that we want
-					 * to rely on it.)
-					 *
-					 * The token location is attached to the run-time
-					 * typecast, not to the Const, for the convenience of
-					 * pg_stat_statements (which doesn't want these constructs
-					 * to appear to be replaceable constants).
-					 */
-					Node *n;
-					n = makeStringConstCast("now", -1, SystemTypeName("text"));
-					$$ = makeTypeCast(n, SystemTypeName("date"), @1);
+					$$ = makeSQLValueFunction(SVFOP_CURRENT_DATE, -1, @1);
 				}
 			| CURRENT_TIME
 				{
-					/*
-					 * Translate as "'now'::text::timetz".
-					 * See comments for CURRENT_DATE.
-					 */
-					Node *n;
-					n = makeStringConstCast("now", -1, SystemTypeName("text"));
-					$$ = makeTypeCast(n, SystemTypeName("timetz"), @1);
+					$$ = makeSQLValueFunction(SVFOP_CURRENT_TIME, -1, @1);
 				}
 			| CURRENT_TIME '(' Iconst ')'
 				{
-					/*
-					 * Translate as "'now'::text::timetz(n)".
-					 * See comments for CURRENT_DATE.
-					 */
-					Node *n;
-					TypeName *d;
-					n = makeStringConstCast("now", -1, SystemTypeName("text"));
-					d = SystemTypeName("timetz");
-					d->typmods = list_make1(makeIntConst($3, @3));
-					$$ = makeTypeCast(n, d, @1);
+					$$ = makeSQLValueFunction(SVFOP_CURRENT_TIME_N, $3, @1);
 				}
 			| CURRENT_TIMESTAMP
 				{
-					/*
-					 * Translate as "now()", since we have a function that
-					 * does exactly what is needed.
-					 */
-					$$ = (Node *) makeFuncCall(SystemFuncName("now"), NIL, @1);
+					$$ = makeSQLValueFunction(SVFOP_CURRENT_TIMESTAMP, -1, @1);
 				}
 			| CURRENT_TIMESTAMP '(' Iconst ')'
 				{
-					/*
-					 * Translate as "'now'::text::timestamptz(n)".
-					 * See comments for CURRENT_DATE.
-					 */
-					Node *n;
-					TypeName *d;
-					n = makeStringConstCast("now", -1, SystemTypeName("text"));
-					d = SystemTypeName("timestamptz");
-					d->typmods = list_make1(makeIntConst($3, @3));
-					$$ = makeTypeCast(n, d, @1);
+					$$ = makeSQLValueFunction(SVFOP_CURRENT_TIMESTAMP_N, $3, @1);
 				}
 			| LOCALTIME
 				{
-					/*
-					 * Translate as "'now'::text::time".
-					 * See comments for CURRENT_DATE.
-					 */
-					Node *n;
-					n = makeStringConstCast("now", -1, SystemTypeName("text"));
-					$$ = makeTypeCast((Node *)n, SystemTypeName("time"), @1);
+					$$ = makeSQLValueFunction(SVFOP_LOCALTIME, -1, @1);
 				}
 			| LOCALTIME '(' Iconst ')'
 				{
-					/*
-					 * Translate as "'now'::text::time(n)".
-					 * See comments for CURRENT_DATE.
-					 */
-					Node *n;
-					TypeName *d;
-					n = makeStringConstCast("now", -1, SystemTypeName("text"));
-					d = SystemTypeName("time");
-					d->typmods = list_make1(makeIntConst($3, @3));
-					$$ = makeTypeCast((Node *)n, d, @1);
+					$$ = makeSQLValueFunction(SVFOP_LOCALTIME_N, $3, @1);
 				}
 			| LOCALTIMESTAMP
 				{
-					/*
-					 * Translate as "'now'::text::timestamp".
-					 * See comments for CURRENT_DATE.
-					 */
-					Node *n;
-					n = makeStringConstCast("now", -1, SystemTypeName("text"));
-					$$ = makeTypeCast(n, SystemTypeName("timestamp"), @1);
+					$$ = makeSQLValueFunction(SVFOP_LOCALTIMESTAMP, -1, @1);
 				}
 			| LOCALTIMESTAMP '(' Iconst ')'
 				{
-					/*
-					 * Translate as "'now'::text::timestamp(n)".
-					 * See comments for CURRENT_DATE.
-					 */
-					Node *n;
-					TypeName *d;
-					n = makeStringConstCast("now", -1, SystemTypeName("text"));
-					d = SystemTypeName("timestamp");
-					d->typmods = list_make1(makeIntConst($3, @3));
-					$$ = makeTypeCast(n, d, @1);
+					$$ = makeSQLValueFunction(SVFOP_LOCALTIMESTAMP_N, $3, @1);
 				}
 			| CURRENT_ROLE
 				{
-					$$ = (Node *) makeFuncCall(SystemFuncName("current_user"), NIL, @1);
+					$$ = makeSQLValueFunction(SVFOP_CURRENT_ROLE, -1, @1);
 				}
 			| CURRENT_USER
 				{
-					$$ = (Node *) makeFuncCall(SystemFuncName("current_user"), NIL, @1);
+					$$ = makeSQLValueFunction(SVFOP_CURRENT_USER, -1, @1);
 				}
 			| SESSION_USER
 				{
-					$$ = (Node *) makeFuncCall(SystemFuncName("session_user"), NIL, @1);
+					$$ = makeSQLValueFunction(SVFOP_SESSION_USER, -1, @1);
 				}
 			| USER
 				{
-					$$ = (Node *) makeFuncCall(SystemFuncName("current_user"), NIL, @1);
+					$$ = makeSQLValueFunction(SVFOP_USER, -1, @1);
 				}
 			| CURRENT_CATALOG
 				{
-					$$ = (Node *) makeFuncCall(SystemFuncName("current_database"), NIL, @1);
+					$$ = makeSQLValueFunction(SVFOP_CURRENT_CATALOG, -1, @1);
 				}
 			| CURRENT_SCHEMA
 				{
-					$$ = (Node *) makeFuncCall(SystemFuncName("current_schema"), NIL, @1);
+					$$ = makeSQLValueFunction(SVFOP_CURRENT_SCHEMA, -1, @1);
 				}
 			| CAST '(' a_expr AS Typename ')'
 				{ $$ = makeTypeCast($3, $5, @1); }
@@ -14711,6 +14633,18 @@ makeAArrayExpr(List *elements, int location)
 }
 
 static Node *
+makeSQLValueFunction(SQLValueFunctionOp op, int32 typmod, int location)
+{
+	SQLValueFunction *svf = makeNode(SQLValueFunction);
+
+	svf->op = op;
+	/* svf->type will be filled during parse analysis */
+	svf->typmod = typmod;
+	svf->location = location;
+	return (Node *) svf;
+}
+
+static Node *
 makeXmlExpr(XmlExprOp op, char *name, List *named_args, List *args,
 			int location)
 {
diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index cead21283d0..63f7965532e 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -34,7 +34,9 @@
 #include "parser/parse_type.h"
 #include "parser/parse_agg.h"
 #include "utils/builtins.h"
+#include "utils/date.h"
 #include "utils/lsyscache.h"
+#include "utils/timestamp.h"
 #include "utils/xml.h"
 
 
@@ -107,6 +109,8 @@ static Node *transformArrayExpr(ParseState *pstate, A_ArrayExpr *a,
 static Node *transformRowExpr(ParseState *pstate, RowExpr *r);
 static Node *transformCoalesceExpr(ParseState *pstate, CoalesceExpr *c);
 static Node *transformMinMaxExpr(ParseState *pstate, MinMaxExpr *m);
+static Node *transformSQLValueFunction(ParseState *pstate,
+						  SQLValueFunction *svf);
 static Node *transformXmlExpr(ParseState *pstate, XmlExpr *x);
 static Node *transformXmlSerialize(ParseState *pstate, XmlSerialize *xs);
 static Node *transformBooleanTest(ParseState *pstate, BooleanTest *b);
@@ -306,6 +310,11 @@ transformExprRecurse(ParseState *pstate, Node *expr)
 			result = transformMinMaxExpr(pstate, (MinMaxExpr *) expr);
 			break;
 
+		case T_SQLValueFunction:
+			result = transformSQLValueFunction(pstate,
+											   (SQLValueFunction *) expr);
+			break;
+
 		case T_XmlExpr:
 			result = transformXmlExpr(pstate, (XmlExpr *) expr);
 			break;
@@ -2179,6 +2188,59 @@ transformMinMaxExpr(ParseState *pstate, MinMaxExpr *m)
 }
 
 static Node *
+transformSQLValueFunction(ParseState *pstate, SQLValueFunction *svf)
+{
+	/*
+	 * All we need to do is insert the correct result type and (where needed)
+	 * validate the typmod, so we just modify the node in-place.
+	 */
+	switch (svf->op)
+	{
+		case SVFOP_CURRENT_DATE:
+			svf->type = DATEOID;
+			break;
+		case SVFOP_CURRENT_TIME:
+			svf->type = TIMETZOID;
+			break;
+		case SVFOP_CURRENT_TIME_N:
+			svf->type = TIMETZOID;
+			svf->typmod = anytime_typmod_check(true, svf->typmod);
+			break;
+		case SVFOP_CURRENT_TIMESTAMP:
+			svf->type = TIMESTAMPTZOID;
+			break;
+		case SVFOP_CURRENT_TIMESTAMP_N:
+			svf->type = TIMESTAMPTZOID;
+			svf->typmod = anytimestamp_typmod_check(true, svf->typmod);
+			break;
+		case SVFOP_LOCALTIME:
+			svf->type = TIMEOID;
+			break;
+		case SVFOP_LOCALTIME_N:
+			svf->type = TIMEOID;
+			svf->typmod = anytime_typmod_check(false, svf->typmod);
+			break;
+		case SVFOP_LOCALTIMESTAMP:
+			svf->type = TIMESTAMPOID;
+			break;
+		case SVFOP_LOCALTIMESTAMP_N:
+			svf->type = TIMESTAMPOID;
+			svf->typmod = anytimestamp_typmod_check(false, svf->typmod);
+			break;
+		case SVFOP_CURRENT_ROLE:
+		case SVFOP_CURRENT_USER:
+		case SVFOP_USER:
+		case SVFOP_SESSION_USER:
+		case SVFOP_CURRENT_CATALOG:
+		case SVFOP_CURRENT_SCHEMA:
+			svf->type = NAMEOID;
+			break;
+	}
+
+	return (Node *) svf;
+}
+
+static Node *
 transformXmlExpr(ParseState *pstate, XmlExpr *x)
 {
 	XmlExpr    *newx;
diff --git a/src/backend/parser/parse_target.c b/src/backend/parser/parse_target.c
index fc93063ed0b..b7b82bfb6b1 100644
--- a/src/backend/parser/parse_target.c
+++ b/src/backend/parser/parse_target.c
@@ -1761,6 +1761,49 @@ FigureColnameInternal(Node *node, char **name)
 					return 2;
 			}
 			break;
+		case T_SQLValueFunction:
+			/* make these act like a function or variable */
+			switch (((SQLValueFunction *) node)->op)
+			{
+				case SVFOP_CURRENT_DATE:
+					*name = "current_date";
+					return 2;
+				case SVFOP_CURRENT_TIME:
+				case SVFOP_CURRENT_TIME_N:
+					*name = "current_time";
+					return 2;
+				case SVFOP_CURRENT_TIMESTAMP:
+				case SVFOP_CURRENT_TIMESTAMP_N:
+					*name = "current_timestamp";
+					return 2;
+				case SVFOP_LOCALTIME:
+				case SVFOP_LOCALTIME_N:
+					*name = "localtime";
+					return 2;
+				case SVFOP_LOCALTIMESTAMP:
+				case SVFOP_LOCALTIMESTAMP_N:
+					*name = "localtimestamp";
+					return 2;
+				case SVFOP_CURRENT_ROLE:
+					*name = "current_role";
+					return 2;
+				case SVFOP_CURRENT_USER:
+					*name = "current_user";
+					return 2;
+				case SVFOP_USER:
+					*name = "user";
+					return 2;
+				case SVFOP_SESSION_USER:
+					*name = "session_user";
+					return 2;
+				case SVFOP_CURRENT_CATALOG:
+					*name = "current_catalog";
+					return 2;
+				case SVFOP_CURRENT_SCHEMA:
+					*name = "current_schema";
+					return 2;
+			}
+			break;
 		case T_XmlExpr:
 			/* make SQL/XML functions act like a regular function */
 			switch (((XmlExpr *) node)->op)