Fix under-parenthesized display of AT TIME ZONE constructs.

In commit 40c24bfef, I forgot to use get_rule_expr_paren() for the
arguments of AT TIME ZONE, resulting in possibly not printing parens
for expressions that need it.  But get_rule_expr_paren() wouldn't have
gotten it right anyway, because isSimpleNode() hadn't been taught that
COERCE_SQL_SYNTAX parent nodes don't guarantee sufficient parentheses.
Improve all that.  Also use this methodology for F_IS_NORMALIZED, so
that we don't print useless parens for that.

In passing, remove a comment that was obsoleted later.

Per report from Duncan Sands.  Back-patch to v14 where this code
came in.  (Before that, we didn't try to print AT TIME ZONE that way,
so there was no bug just ugliness.)

Discussion: https://postgr.es/m/f41566aa-a057-6628-4b7c-b48770ecb84a@deepbluecap.com

src/backend/utils/adt/ruleutils.c

@@ -8254,11 +8254,12 @@ isSimpleNode(Node *node, Node *parentNode, int prettyFlags)
 			{
 				case T_FuncExpr:
 					{
-						/* special handling for casts */
+						/* special handling for casts and COERCE_SQL_SYNTAX */
 						CoercionForm type = ((FuncExpr *) parentNode)->funcformat;
 
 						if (type == COERCE_EXPLICIT_CAST ||
-							type == COERCE_IMPLICIT_CAST)
+							type == COERCE_IMPLICIT_CAST ||
+							type == COERCE_SQL_SYNTAX)
 							return false;
 						return true;	/* own parentheses */
 					}
@@ -8306,11 +8307,12 @@ isSimpleNode(Node *node, Node *parentNode, int prettyFlags)
 					return false;
 				case T_FuncExpr:
 					{
-						/* special handling for casts */
+						/* special handling for casts and COERCE_SQL_SYNTAX */
 						CoercionForm type = ((FuncExpr *) parentNode)->funcformat;
 
 						if (type == COERCE_EXPLICIT_CAST ||
-							type == COERCE_IMPLICIT_CAST)
+							type == COERCE_IMPLICIT_CAST ||
+							type == COERCE_SQL_SYNTAX)
 							return false;
 						return true;	/* own parentheses */
 					}
@@ -10046,9 +10048,11 @@ get_func_sql_syntax(FuncExpr *expr, deparse_context *context)
 		case F_TIMEZONE_TEXT_TIMETZ:
 			/* AT TIME ZONE ... note reversed argument order */
 			appendStringInfoChar(buf, '(');
-			get_rule_expr((Node *) lsecond(expr->args), context, false);
+			get_rule_expr_paren((Node *) lsecond(expr->args), context, false,
+								(Node *) expr);
 			appendStringInfoString(buf, " AT TIME ZONE ");
-			get_rule_expr((Node *) linitial(expr->args), context, false);
+			get_rule_expr_paren((Node *) linitial(expr->args), context, false,
+								(Node *) expr);
 			appendStringInfoChar(buf, ')');
 			return true;
 
@@ -10100,9 +10104,10 @@ get_func_sql_syntax(FuncExpr *expr, deparse_context *context)
 
 		case F_IS_NORMALIZED:
 			/* IS xxx NORMALIZED */
-			appendStringInfoString(buf, "((");
-			get_rule_expr((Node *) linitial(expr->args), context, false);
-			appendStringInfoString(buf, ") IS");
+			appendStringInfoString(buf, "(");
+			get_rule_expr_paren((Node *) linitial(expr->args), context, false,
+								(Node *) expr);
+			appendStringInfoString(buf, " IS");
 			if (list_length(expr->args) == 2)
 			{
 				Const	   *con = (Const *) lsecond(expr->args);
@@ -10123,11 +10128,6 @@ get_func_sql_syntax(FuncExpr *expr, deparse_context *context)
 			appendStringInfoChar(buf, ')');
 			return true;
 
-			/*
-			 * XXX EXTRACT, a/k/a date_part(), is intentionally not covered
-			 * yet.  Add it after we change the return type to numeric.
-			 */
-
 		case F_NORMALIZE:
 			/* NORMALIZE() */
 			appendStringInfoString(buf, "NORMALIZE(");

src/test/regress/expected/create_view.out

@@ -1922,6 +1922,7 @@ select pg_get_viewdef('tt20v', true);
 -- reverse-listing of various special function syntaxes required by SQL
 create view tt201v as
 select
+  ('2022-12-01'::date + '1 day'::interval) at time zone 'UTC' as atz,
   extract(day from now()) as extr,
   (now(), '1 day'::interval) overlaps
     (current_timestamp(2), '1 day'::interval) as o,
@@ -1976,10 +1977,11 @@ select
 select pg_get_viewdef('tt201v', true);
                                         pg_get_viewdef                                         
 -----------------------------------------------------------------------------------------------
-  SELECT EXTRACT(day FROM now()) AS extr,                                                     +
+  SELECT (('12-01-2022'::date + '@ 1 day'::interval) AT TIME ZONE 'UTC'::text) AS atz,        +
+     EXTRACT(day FROM now()) AS extr,                                                         +
      ((now(), '@ 1 day'::interval) OVERLAPS (CURRENT_TIMESTAMP(2), '@ 1 day'::interval)) AS o,+
-     (('foo'::text) IS NORMALIZED) AS isn,                                                    +
-     (('foo'::text) IS NFKC NORMALIZED) AS isnn,                                              +
+     ('foo'::text IS NORMALIZED) AS isn,                                                      +
+     ('foo'::text IS NFKC NORMALIZED) AS isnn,                                                +
      NORMALIZE('foo'::text) AS n,                                                             +
      NORMALIZE('foo'::text, NFKD) AS nfkd,                                                    +
      OVERLAY('foo'::text PLACING 'bar'::text FROM 2) AS ovl,                                  +

src/test/regress/sql/create_view.sql

@@ -703,6 +703,7 @@ select pg_get_viewdef('tt20v', true);
 
 create view tt201v as
 select
+  ('2022-12-01'::date + '1 day'::interval) at time zone 'UTC' as atz,
   extract(day from now()) as extr,
   (now(), '1 day'::interval) overlaps
     (current_timestamp(2), '1 day'::interval) as o,