Desupport jsonb subscript deletion on objects

Supporting deletion of JSON pairs within jsonb objects using an
array-style integer subscript allowed for surprising outcomes.  This was
mostly due to the implementation-defined ordering of pairs within
objects for jsonb.

It also seems desirable to make jsonb integer subscript deletion
consistent with the 9.4 era general purpose integer subscripting
operator for jsonb (although that operator returns NULL when an object
is encountered, while we prefer here to throw an error).

Peter Geoghegan, following discussion on -hackers.

doc/src/sgml/func.sgml

@@ -10309,8 +10309,9 @@ table2-mapping
        <row>
         <entry><literal>-</literal></entry>
         <entry><type>integer</type></entry>
-        <entry>Delete the field or element with specified index (Negative
+        <entry>Delete the array element with specified index (Negative
-        integers count from the end)</entry>
+        integers count from the end).  Throws an error if top level
+        container is not an array.</entry>
         <entry><literal>'["a", "b"]'::jsonb - 1 </literal></entry>
        </row>
        <row>

src/backend/utils/adt/jsonfuncs.c

@@ -3400,6 +3400,11 @@ jsonb_delete_idx(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("cannot delete from scalar")));
 
+	if (JB_ROOT_IS_OBJECT(in))
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("cannot delete from object using integer subscript")));
+
 	if (JB_ROOT_COUNT(in) == 0)
 		PG_RETURN_JSONB(in);
 

src/test/regress/expected/jsonb.out

@@ -3031,54 +3031,6 @@ select '["a","b","c"]'::jsonb - -4;
  ["a", "b", "c"]
 (1 row)
 
-select '{"a":1, "b":2, "c":3}'::jsonb - 3;
-         ?column?         
---------------------------
- {"a": 1, "b": 2, "c": 3}
-(1 row)
-
-select '{"a":1, "b":2, "c":3}'::jsonb - 2;
-     ?column?     
-------------------
- {"a": 1, "b": 2}
-(1 row)
-
-select '{"a":1, "b":2, "c":3}'::jsonb - 1;
-     ?column?     
-------------------
- {"a": 1, "c": 3}
-(1 row)
-
-select '{"a":1, "b":2, "c":3}'::jsonb - 0;
-     ?column?     
-------------------
- {"b": 2, "c": 3}
-(1 row)
-
-select '{"a":1, "b":2, "c":3}'::jsonb - -1;
-     ?column?     
-------------------
- {"a": 1, "b": 2}
-(1 row)
-
-select '{"a":1, "b":2, "c":3}'::jsonb - -2;
-     ?column?     
-------------------
- {"a": 1, "c": 3}
-(1 row)
-
-select '{"a":1, "b":2, "c":3}'::jsonb - -3;
-     ?column?     
-------------------
- {"b": 2, "c": 3}
-(1 row)
-
-select '{"a":1, "b":2, "c":3}'::jsonb - -4;
-         ?column?         
---------------------------
- {"a": 1, "b": 2, "c": 3}
-(1 row)
-
 select jsonb_set('{"n":null, "a":1, "b":[1,2], "c":{"1":2}, "d":{"1":[2,3]}}'::jsonb, '{n}', '[1,2,3]');
                                 jsonb_set                                 
 --------------------------------------------------------------------------
@@ -3192,12 +3144,8 @@ select '[]'::jsonb - 'a';
 
 select '"a"'::jsonb - 1; -- error
 ERROR:  cannot delete from scalar
-select '{}'::jsonb -  1 ;
+select '{}'::jsonb -  1; -- error
- ?column? 
+ERROR:  cannot delete from object using integer subscript
-----------
- {}
-(1 row)
-
 select '[]'::jsonb - 1;
  ?column? 
 ----------

src/test/regress/expected/jsonb_1.out

@@ -3031,54 +3031,6 @@ select '["a","b","c"]'::jsonb - -4;
  ["a", "b", "c"]
 (1 row)
 
-select '{"a":1, "b":2, "c":3}'::jsonb - 3;
-         ?column?         
---------------------------
- {"a": 1, "b": 2, "c": 3}
-(1 row)
-
-select '{"a":1, "b":2, "c":3}'::jsonb - 2;
-     ?column?     
-------------------
- {"a": 1, "b": 2}
-(1 row)
-
-select '{"a":1, "b":2, "c":3}'::jsonb - 1;
-     ?column?     
-------------------
- {"a": 1, "c": 3}
-(1 row)
-
-select '{"a":1, "b":2, "c":3}'::jsonb - 0;
-     ?column?     
-------------------
- {"b": 2, "c": 3}
-(1 row)
-
-select '{"a":1, "b":2, "c":3}'::jsonb - -1;
-     ?column?     
-------------------
- {"a": 1, "b": 2}
-(1 row)
-
-select '{"a":1, "b":2, "c":3}'::jsonb - -2;
-     ?column?     
-------------------
- {"a": 1, "c": 3}
-(1 row)
-
-select '{"a":1, "b":2, "c":3}'::jsonb - -3;
-     ?column?     
-------------------
- {"b": 2, "c": 3}
-(1 row)
-
-select '{"a":1, "b":2, "c":3}'::jsonb - -4;
-         ?column?         
---------------------------
- {"a": 1, "b": 2, "c": 3}
-(1 row)
-
 select jsonb_set('{"n":null, "a":1, "b":[1,2], "c":{"1":2}, "d":{"1":[2,3]}}'::jsonb, '{n}', '[1,2,3]');
                                 jsonb_set                                 
 --------------------------------------------------------------------------
@@ -3192,12 +3144,8 @@ select '[]'::jsonb - 'a';
 
 select '"a"'::jsonb - 1; -- error
 ERROR:  cannot delete from scalar
-select '{}'::jsonb -  1 ;
+select '{}'::jsonb -  1; -- error
- ?column? 
+ERROR:  cannot delete from object using integer subscript
-----------
- {}
-(1 row)
-
 select '[]'::jsonb - 1;
  ?column? 
 ----------

src/test/regress/sql/jsonb.sql

@@ -738,15 +738,6 @@ select '["a","b","c"]'::jsonb - -2;
 select '["a","b","c"]'::jsonb - -3;
 select '["a","b","c"]'::jsonb - -4;
 
-select '{"a":1, "b":2, "c":3}'::jsonb - 3;
-select '{"a":1, "b":2, "c":3}'::jsonb - 2;
-select '{"a":1, "b":2, "c":3}'::jsonb - 1;
-select '{"a":1, "b":2, "c":3}'::jsonb - 0;
-select '{"a":1, "b":2, "c":3}'::jsonb - -1;
-select '{"a":1, "b":2, "c":3}'::jsonb - -2;
-select '{"a":1, "b":2, "c":3}'::jsonb - -3;
-select '{"a":1, "b":2, "c":3}'::jsonb - -4;
-
 select jsonb_set('{"n":null, "a":1, "b":[1,2], "c":{"1":2}, "d":{"1":[2,3]}}'::jsonb, '{n}', '[1,2,3]');
 select jsonb_set('{"n":null, "a":1, "b":[1,2], "c":{"1":2}, "d":{"1":[2,3]}}'::jsonb, '{b,-1}', '[1,2,3]');
 select jsonb_set('{"n":null, "a":1, "b":[1,2], "c":{"1":2}, "d":{"1":[2,3]}}'::jsonb, '{d,1,0}', '[1,2,3]');
@@ -775,7 +766,7 @@ select '"a"'::jsonb - 'a'; -- error
 select '{}'::jsonb - 'a';
 select '[]'::jsonb - 'a';
 select '"a"'::jsonb - 1; -- error
-select '{}'::jsonb -  1 ;
+select '{}'::jsonb -  1; -- error
 select '[]'::jsonb - 1;
 select '"a"'::jsonb - '{a}'::text[]; -- error
 select '{}'::jsonb - '{a}'::text[];