interval: tighten precision specification

interval precision can only be specified after the "interval" keyword if
no units are specified.

Previously we incorrectly checked the units to see if the precision was
legal, causing confusion.

Report by Alvaro Herrera

src/backend/parser/gram.y

@@ -1552,25 +1552,9 @@ zone_value:
 					t->typmods = $3;
 					$$ = makeStringConstCast($2, @2, t);
 				}
-			| ConstInterval '(' Iconst ')' Sconst opt_interval
+			| ConstInterval '(' Iconst ')' Sconst
 				{
 					TypeName *t = $1;
-					if ($6 != NIL)
-					{
-						A_Const *n = (A_Const *) linitial($6);
-						if ((n->val.val.ival & ~(INTERVAL_MASK(HOUR) | INTERVAL_MASK(MINUTE))) != 0)
-							ereport(ERROR,
-									(errcode(ERRCODE_SYNTAX_ERROR),
-									 errmsg("time zone interval must be HOUR or HOUR TO MINUTE"),
-									 parser_errposition(@6)));
-						if (list_length($6) != 1)
-							ereport(ERROR,
-									(errcode(ERRCODE_SYNTAX_ERROR),
-									 errmsg("interval precision specified twice"),
-									 parser_errposition(@1)));
-						t->typmods = lappend($6, makeIntConst($3, @3));
-					}
-					else
 					t->typmods = list_make2(makeIntConst(INTERVAL_FULL_RANGE, -1),
 											makeIntConst($3, @3));
 					$$ = makeStringConstCast($5, @5, t);
@@ -10582,19 +10566,9 @@ SimpleTypename:
 					$$ = $1;
 					$$->typmods = $2;
 				}
-			| ConstInterval '(' Iconst ')' opt_interval
+			| ConstInterval '(' Iconst ')'
 				{
 					$$ = $1;
-					if ($5 != NIL)
-					{
-						if (list_length($5) != 1)
-							ereport(ERROR,
-									(errcode(ERRCODE_SYNTAX_ERROR),
-									 errmsg("interval precision specified twice"),
-									 parser_errposition(@1)));
-						$$->typmods = lappend($5, makeIntConst($3, @3));
-					}
-					else
 					$$->typmods = list_make2(makeIntConst(INTERVAL_FULL_RANGE, -1),
 											 makeIntConst($3, @3));
 				}
@@ -12923,19 +12897,9 @@ AexprConst: Iconst
 					t->typmods = $3;
 					$$ = makeStringConstCast($2, @2, t);
 				}
-			| ConstInterval '(' Iconst ')' Sconst opt_interval
+			| ConstInterval '(' Iconst ')' Sconst
 				{
 					TypeName *t = $1;
-					if ($6 != NIL)
-					{
-						if (list_length($6) != 1)
-							ereport(ERROR,
-									(errcode(ERRCODE_SYNTAX_ERROR),
-									 errmsg("interval precision specified twice"),
-									 parser_errposition(@1)));
-						t->typmods = lappend($6, makeIntConst($3, @3));
-					}
-					else
 					t->typmods = list_make2(makeIntConst(INTERVAL_FULL_RANGE, -1),
 											makeIntConst($3, @3));
 					$$ = makeStringConstCast($5, @5, t);

src/test/regress/expected/interval.out

@@ -616,16 +616,6 @@ SELECT interval '12:34.5678' minute to second(2);  -- per SQL spec
  00:12:34.57
 (1 row)
 
-SELECT interval(2) '12:34.5678' minute to second;  -- historical PG
-  interval   
--------------
- 00:12:34.57
-(1 row)
-
-SELECT interval(2) '12:34.5678' minute to second(2);  -- syntax error
-ERROR:  interval precision specified twice
-LINE 1: SELECT interval(2) '12:34.5678' minute to second(2);
-               ^
 SELECT interval '1.234' second;
    interval   
 --------------

src/test/regress/sql/interval.sql

@@ -183,8 +183,6 @@ SELECT interval '123 2:03 -2:04'; -- not ok, redundant hh:mm fields
 SELECT interval(0) '1 day 01:23:45.6789';
 SELECT interval(2) '1 day 01:23:45.6789';
 SELECT interval '12:34.5678' minute to second(2);  -- per SQL spec
-SELECT interval(2) '12:34.5678' minute to second;  -- historical PG
-SELECT interval(2) '12:34.5678' minute to second(2);  -- syntax error
 SELECT interval '1.234' second;
 SELECT interval '1.234' second(2);
 SELECT interval '1 2.345' day to second(2);