Remove undocumented IS [NOT] OF syntax.

This feature was added a long time ago, in 7c1e67bd and eb121ba2,
but never documented in any user-facing way.  (Documentation added
in 6126d3e7 was commented out almost immediately, in 8272fc3f.)
That's because, while this syntax is defined by SQL:99, our
implementation is only vaguely related to the standard's semantics.
The standard appears to intend a run-time not parse-time test, and
it definitely intends that the test should understand subtype
relationships.

No one has stepped up to fix that in the intervening years, but
people keep coming across the code and asking why it's not documented.
Let's just get rid of it: if anyone ever wants to make it work per
spec, they can easily recover whatever parts of this code are still
of value from our git history.

If there's anyone out there who's actually using this despite its
undocumented status, they can switch to using pg_typeof() instead,
eg. "pg_typeof(something) = 'mytype'::regtype".  That gives
essentially the same semantics as what our IS OF code did.
(We didn't have that function last time this was discussed, or
we would have ripped out IS OF then.)

Discussion: https://postgr.es/m/CAKFQuwZ2pTc-DSkOiTfjauqLYkNREeNZvWmeg12Q-_69D+sYZA@mail.gmail.com
Discussion: https://postgr.es/m/BAY20-F23E9F2B4DAB3E4E88D3623F99B0@phx.gbl
Discussion: https://postgr.es/m/3E7CF81D.1000203@joeconway.com

doc/src/sgml/func.sgml

@@ -762,25 +762,6 @@ repeat('Pg', 4) <returnvalue>PgPgPgPg</returnvalue>
     expression must be of Boolean type.
    </para>
 
-<!-- IS OF does not conform to the ISO SQL behavior, so it is undocumented here
-   <para>
-    <indexterm>
-     <primary>IS OF</primary>
-    </indexterm>
-    <indexterm>
-     <primary>IS NOT OF</primary>
-    </indexterm>
-    It is possible to check the data type of an expression using the
-    predicates
-<synopsis>
-<replaceable>expression</replaceable> IS OF (typename, ...)
-<replaceable>expression</replaceable> IS NOT OF (typename, ...)
-</synopsis>
-    They return a boolean value based on whether the expression's data
-    type is one of the listed data types.
-   </para>
--->
-
    <para>
     Some comparison-related functions are also available, as shown in <xref
     linkend="functions-comparison-func-table"/>.

src/backend/catalog/sql_features.txt

@@ -373,7 +373,7 @@ S096	Optional array bounds			YES
 S097	Array element assignment			NO	
 S098	ARRAY_AGG			YES	
 S111	ONLY in query expressions			YES	
-S151	Type predicate			NO	
+S151	Type predicate			NO	see pg_typeof()
 S161	Subtype treatment			NO	
 S162	Subtype treatment for references			NO	
 S201	SQL-invoked routines on arrays			YES	

src/backend/nodes/outfuncs.c

@@ -3213,10 +3213,6 @@ _outAExpr(StringInfo str, const A_Expr *node)
 			appendStringInfoString(str, " NULLIF ");
 			WRITE_NODE_FIELD(name);
 			break;
-		case AEXPR_OF:
-			appendStringInfoString(str, " OF ");
-			WRITE_NODE_FIELD(name);
-			break;
 		case AEXPR_IN:
 			appendStringInfoString(str, " IN ");
 			WRITE_NODE_FIELD(name);

src/backend/parser/gram.y

@@ -13238,14 +13238,6 @@ a_expr:		c_expr									{ $$ = $1; }
 				{
 					$$ = (Node *) makeSimpleA_Expr(AEXPR_NOT_DISTINCT, "=", $1, $6, @2);
 				}
-			| a_expr IS OF '(' type_list ')'			%prec IS
-				{
-					$$ = (Node *) makeSimpleA_Expr(AEXPR_OF, "=", $1, (Node *) $5, @2);
-				}
-			| a_expr IS NOT OF '(' type_list ')'		%prec IS
-				{
-					$$ = (Node *) makeSimpleA_Expr(AEXPR_OF, "<>", $1, (Node *) $6, @2);
-				}
 			| a_expr BETWEEN opt_asymmetric b_expr AND a_expr		%prec BETWEEN
 				{
 					$$ = (Node *) makeSimpleA_Expr(AEXPR_BETWEEN,
@@ -13464,14 +13456,6 @@ b_expr:		c_expr
 				{
 					$$ = (Node *) makeSimpleA_Expr(AEXPR_NOT_DISTINCT, "=", $1, $6, @2);
 				}
-			| b_expr IS OF '(' type_list ')'		%prec IS
-				{
-					$$ = (Node *) makeSimpleA_Expr(AEXPR_OF, "=", $1, (Node *) $5, @2);
-				}
-			| b_expr IS NOT OF '(' type_list ')'	%prec IS
-				{
-					$$ = (Node *) makeSimpleA_Expr(AEXPR_OF, "<>", $1, (Node *) $6, @2);
-				}
 			| b_expr IS DOCUMENT_P					%prec IS
 				{
 					$$ = makeXmlExpr(IS_DOCUMENT, NULL, NIL,

src/backend/parser/parse_expr.c

@@ -94,7 +94,6 @@ static Node *transformAExprOpAny(ParseState *pstate, A_Expr *a);
 static Node *transformAExprOpAll(ParseState *pstate, A_Expr *a);
 static Node *transformAExprDistinct(ParseState *pstate, A_Expr *a);
 static Node *transformAExprNullIf(ParseState *pstate, A_Expr *a);
-static Node *transformAExprOf(ParseState *pstate, A_Expr *a);
 static Node *transformAExprIn(ParseState *pstate, A_Expr *a);
 static Node *transformAExprBetween(ParseState *pstate, A_Expr *a);
 static Node *transformBoolExpr(ParseState *pstate, BoolExpr *a);
@@ -228,9 +227,6 @@ transformExprRecurse(ParseState *pstate, Node *expr)
 					case AEXPR_NULLIF:
 						result = transformAExprNullIf(pstate, a);
 						break;
-					case AEXPR_OF:
-						result = transformAExprOf(pstate, a);
-						break;
 					case AEXPR_IN:
 						result = transformAExprIn(pstate, a);
 						break;
@@ -1168,51 +1164,6 @@ transformAExprNullIf(ParseState *pstate, A_Expr *a)
 	return (Node *) result;
 }
 
-/*
- * Checking an expression for match to a list of type names. Will result
- * in a boolean constant node.
- */
-static Node *
-transformAExprOf(ParseState *pstate, A_Expr *a)
-{
-	Node	   *lexpr = a->lexpr;
-	Const	   *result;
-	ListCell   *telem;
-	Oid			ltype,
-				rtype;
-	bool		matched = false;
-
-	if (operator_precedence_warning)
-		emit_precedence_warnings(pstate, PREC_GROUP_POSTFIX_IS, "IS",
-								 lexpr, NULL,
-								 a->location);
-
-	lexpr = transformExprRecurse(pstate, lexpr);
-
-	ltype = exprType(lexpr);
-	foreach(telem, (List *) a->rexpr)
-	{
-		rtype = typenameTypeId(pstate, lfirst(telem));
-		matched = (rtype == ltype);
-		if (matched)
-			break;
-	}
-
-	/*
-	 * We have two forms: equals or not equals. Flip the sense of the result
-	 * for not equals.
-	 */
-	if (strcmp(strVal(linitial(a->name)), "<>") == 0)
-		matched = (!matched);
-
-	result = (Const *) makeBoolConst(matched, false);
-
-	/* Make the result have the original input's parse location */
-	result->location = exprLocation((Node *) a);
-
-	return (Node *) result;
-}
-
 static Node *
 transformAExprIn(ParseState *pstate, A_Expr *a)
 {
@@ -3257,11 +3208,6 @@ operator_precedence_group(Node *node, const char **nodename)
 			*nodename = "IS";
 			group = PREC_GROUP_INFIX_IS;
 		}
-		else if (aexpr->kind == AEXPR_OF)
-		{
-			*nodename = "IS";
-			group = PREC_GROUP_POSTFIX_IS;
-		}
 		else if (aexpr->kind == AEXPR_IN)
 		{
 			*nodename = "IN";

src/include/nodes/parsenodes.h

@@ -258,7 +258,6 @@ typedef enum A_Expr_Kind
 	AEXPR_DISTINCT,				/* IS DISTINCT FROM - name must be "=" */
 	AEXPR_NOT_DISTINCT,			/* IS NOT DISTINCT FROM - name must be "=" */
 	AEXPR_NULLIF,				/* NULLIF - name must be "=" */
-	AEXPR_OF,					/* IS [NOT] OF - name must be "=" or "<>" */
 	AEXPR_IN,					/* [NOT] IN - name must be "=" or "<>" */
 	AEXPR_LIKE,					/* [NOT] LIKE - name must be "~~" or "!~~" */
 	AEXPR_ILIKE,				/* [NOT] ILIKE - name must be "~~*" or "!~~*" */

src/test/regress/expected/arrays.out

@@ -1149,10 +1149,10 @@ SELECT ARRAY[1,2,3]::text[]::int[]::float8[] AS "{1,2,3}";
  {1,2,3}
 (1 row)
 
-SELECT ARRAY[1,2,3]::text[]::int[]::float8[] is of (float8[]) as "TRUE";
- TRUE 
-------
- t
+SELECT pg_typeof(ARRAY[1,2,3]::text[]::int[]::float8[]) AS "double precision[]";
+ double precision[] 
+--------------------
+ double precision[]
 (1 row)
 
 SELECT ARRAY[['a','bc'],['def','hijk']]::text[]::varchar[] AS "{{a,bc},{def,hijk}}";
@@ -1161,10 +1161,10 @@ SELECT ARRAY[['a','bc'],['def','hijk']]::text[]::varchar[] AS "{{a,bc},{def,hijk
  {{a,bc},{def,hijk}}
 (1 row)
 
-SELECT ARRAY[['a','bc'],['def','hijk']]::text[]::varchar[] is of (varchar[]) as "TRUE";
- TRUE 
-------
- t
+SELECT pg_typeof(ARRAY[['a','bc'],['def','hijk']]::text[]::varchar[]) AS "character varying[]";
+ character varying[] 
+---------------------
+ character varying[]
 (1 row)
 
 SELECT CAST(ARRAY[[[[[['a','bb','ccc']]]]]] as text[]) as "{{{{{{a,bb,ccc}}}}}}";

src/test/regress/expected/domain.out

@@ -70,22 +70,16 @@ from basictest;
 (3 rows)
 
 -- check that union/case/coalesce type resolution handles domains properly
-select coalesce(4::domainint4, 7) is of (int4) as t;
- t 
----
- t
-(1 row)
-
-select coalesce(4::domainint4, 7) is of (domainint4) as f;
- f 
----
- f
+select pg_typeof(coalesce(4::domainint4, 7));
+ pg_typeof 
+-----------
+ integer
 (1 row)
 
-select coalesce(4::domainint4, 7::domainint4) is of (domainint4) as t;
- t 
----
- t
+select pg_typeof(coalesce(4::domainint4, 7::domainint4));
+ pg_typeof  
+------------
+ domainint4
 (1 row)
 
 drop table basictest;

src/test/regress/expected/with.out

@@ -142,10 +142,10 @@ SELECT * FROM t LIMIT 10;
 
 -- Test behavior with an unknown-type literal in the WITH
 WITH q AS (SELECT 'foo' AS x)
-SELECT x, x IS OF (text) AS is_text FROM q;
-  x  | is_text 
------+---------
- foo | t
+SELECT x, pg_typeof(x) FROM q;
+  x  | pg_typeof 
+-----+-----------
+ foo | text
 (1 row)
 
 WITH RECURSIVE t(n) AS (
@@ -153,15 +153,15 @@ WITH RECURSIVE t(n) AS (
 UNION ALL
     SELECT n || ' bar' FROM t WHERE length(n) < 20
 )
-SELECT n, n IS OF (text) AS is_text FROM t;
-            n            | is_text 
--------------------------+---------
- foo                     | t
- foo bar                 | t
- foo bar bar             | t
- foo bar bar bar         | t
- foo bar bar bar bar     | t
- foo bar bar bar bar bar | t
+SELECT n, pg_typeof(n) FROM t;
+            n            | pg_typeof 
+-------------------------+-----------
+ foo                     | text
+ foo bar                 | text
+ foo bar bar             | text
+ foo bar bar bar         | text
+ foo bar bar bar bar     | text
+ foo bar bar bar bar bar | text
 (6 rows)
 
 -- In a perfect world, this would work and resolve the literal as int ...
@@ -171,7 +171,7 @@ WITH RECURSIVE t(n) AS (
 UNION ALL
     SELECT n+1 FROM t WHERE n < 10
 )
-SELECT n, n IS OF (int) AS is_int FROM t;
+SELECT n, pg_typeof(n) FROM t;
 ERROR:  operator does not exist: text + integer
 LINE 4:     SELECT n+1 FROM t WHERE n < 10
                     ^

src/test/regress/sql/arrays.sql

@@ -343,9 +343,9 @@ SELECT * FROM array_op_test WHERE t <@ '{}' ORDER BY seqno;
 
 -- array casts
 SELECT ARRAY[1,2,3]::text[]::int[]::float8[] AS "{1,2,3}";
-SELECT ARRAY[1,2,3]::text[]::int[]::float8[] is of (float8[]) as "TRUE";
+SELECT pg_typeof(ARRAY[1,2,3]::text[]::int[]::float8[]) AS "double precision[]";
 SELECT ARRAY[['a','bc'],['def','hijk']]::text[]::varchar[] AS "{{a,bc},{def,hijk}}";
-SELECT ARRAY[['a','bc'],['def','hijk']]::text[]::varchar[] is of (varchar[]) as "TRUE";
+SELECT pg_typeof(ARRAY[['a','bc'],['def','hijk']]::text[]::varchar[]) AS "character varying[]";
 SELECT CAST(ARRAY[[[[[['a','bb','ccc']]]]]] as text[]) as "{{{{{{a,bb,ccc}}}}}}";
 SELECT NULL::text[]::int[] AS "NULL";
 

src/test/regress/sql/domain.sql

@@ -59,9 +59,8 @@ select testtext || testvarchar as concat, testnumeric + 42 as sum
 from basictest;
 
 -- check that union/case/coalesce type resolution handles domains properly
-select coalesce(4::domainint4, 7) is of (int4) as t;
-select coalesce(4::domainint4, 7) is of (domainint4) as f;
-select coalesce(4::domainint4, 7::domainint4) is of (domainint4) as t;
+select pg_typeof(coalesce(4::domainint4, 7));
+select pg_typeof(coalesce(4::domainint4, 7::domainint4));
 
 drop table basictest;
 drop domain domainvarchar restrict;

src/test/regress/sql/with.sql

@@ -77,14 +77,14 @@ SELECT * FROM t LIMIT 10;
 
 -- Test behavior with an unknown-type literal in the WITH
 WITH q AS (SELECT 'foo' AS x)
-SELECT x, x IS OF (text) AS is_text FROM q;
+SELECT x, pg_typeof(x) FROM q;
 
 WITH RECURSIVE t(n) AS (
     SELECT 'foo'
 UNION ALL
     SELECT n || ' bar' FROM t WHERE length(n) < 20
 )
-SELECT n, n IS OF (text) AS is_text FROM t;
+SELECT n, pg_typeof(n) FROM t;
 
 -- In a perfect world, this would work and resolve the literal as int ...
 -- but for now, we have to be content with resolving to text too soon.
@@ -93,7 +93,7 @@ WITH RECURSIVE t(n) AS (
 UNION ALL
     SELECT n+1 FROM t WHERE n < 10
 )
-SELECT n, n IS OF (int) AS is_int FROM t;
+SELECT n, pg_typeof(n) FROM t;
 
 --
 -- Some examples with a tree