Get rid of more cases of the "must detoast before output function" meme.

I missed that json.c was doing this too, because for some bizarre reason
it wasn't doing it adjacent to the output function call.

src/backend/utils/adt/json.c

@@ -1425,8 +1425,7 @@ composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 
 	for (i = 0; i < tupdesc->natts; i++)
 	{
-		Datum		val,
-					origval;
+		Datum		val;
 		bool		isnull;
 		char	   *attname;
 		TYPCATEGORY tcategory;
@@ -1445,7 +1444,7 @@ composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 		escape_json(result, attname);
 		appendStringInfoChar(result, ':');
 
-		origval = heap_getattr(tuple, i + 1, tupdesc, &isnull);
+		val = heap_getattr(tuple, i + 1, tupdesc, &isnull);
 
 		getTypeOutputInfo(tupdesc->attrs[i]->atttypid,
 						  &typoutput, &typisvarlena);
@@ -1480,20 +1479,7 @@ composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 		else
 			tcategory = TypeCategory(tupdesc->attrs[i]->atttypid);
 
-		/*
-		 * If we have a toasted datum, forcibly detoast it here to avoid
-		 * memory leakage inside the type's output routine.
-		 */
-		if (typisvarlena && !isnull)
-			val = PointerGetDatum(PG_DETOAST_DATUM(origval));
-		else
-			val = origval;
-
 		datum_to_json(val, isnull, result, tcategory, typoutput);
-
-		/* Clean up detoasted copy, if any */
-		if (val != origval)
-			pfree(DatumGetPointer(val));
 	}
 
 	appendStringInfoChar(result, '}');
@@ -1572,10 +1558,9 @@ row_to_json_pretty(PG_FUNCTION_ARGS)
 Datum
 to_json(PG_FUNCTION_ARGS)
 {
+	Datum		val = PG_GETARG_DATUM(0);
 	Oid			val_type = get_fn_expr_argtype(fcinfo->flinfo, 0);
 	StringInfo	result;
-	Datum		orig_val,
-				val;
 	TYPCATEGORY tcategory;
 	Oid			typoutput;
 	bool		typisvarlena;
@@ -1586,11 +1571,8 @@ to_json(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("could not determine input data type")));
 
-
 	result = makeStringInfo();
 
-	orig_val = PG_ARGISNULL(0) ? (Datum) 0 : PG_GETARG_DATUM(0);
-
 	getTypeOutputInfo(val_type, &typoutput, &typisvarlena);
 
 	if (val_type > FirstNormalObjectId)
@@ -1623,21 +1605,8 @@ to_json(PG_FUNCTION_ARGS)
 	else
 		tcategory = TypeCategory(val_type);
 
-	/*
-	 * If we have a toasted datum, forcibly detoast it here to avoid memory
-	 * leakage inside the type's output routine.
-	 */
-	if (typisvarlena && orig_val != (Datum) 0)
-		val = PointerGetDatum(PG_DETOAST_DATUM(orig_val));
-	else
-		val = orig_val;
-
 	datum_to_json(val, false, result, tcategory, typoutput);
 
-	/* Clean up detoasted copy, if any */
-	if (val != orig_val)
-		pfree(DatumGetPointer(val));
-
 	PG_RETURN_TEXT_P(cstring_to_text(result->data));
 }
 
@@ -1651,8 +1620,7 @@ json_agg_transfn(PG_FUNCTION_ARGS)
 	MemoryContext aggcontext,
 				oldcontext;
 	StringInfo	state;
-	Datum		orig_val,
-				val;
+	Datum		val;
 	TYPCATEGORY tcategory;
 	Oid			typoutput;
 	bool		typisvarlena;
@@ -1692,13 +1660,12 @@ json_agg_transfn(PG_FUNCTION_ARGS)
 	/* fast path for NULLs */
 	if (PG_ARGISNULL(1))
 	{
-		orig_val = (Datum) 0;
-		datum_to_json(orig_val, true, state, 0, InvalidOid);
+		val = (Datum) 0;
+		datum_to_json(val, true, state, 0, InvalidOid);
 		PG_RETURN_POINTER(state);
 	}
 
-
-	orig_val = PG_GETARG_DATUM(1);
+	val = PG_GETARG_DATUM(1);
 
 	getTypeOutputInfo(val_type, &typoutput, &typisvarlena);
 
@@ -1732,15 +1699,6 @@ json_agg_transfn(PG_FUNCTION_ARGS)
 	else
 		tcategory = TypeCategory(val_type);
 
-	/*
-	 * If we have a toasted datum, forcibly detoast it here to avoid memory
-	 * leakage inside the type's output routine.
-	 */
-	if (typisvarlena)
-		val = PointerGetDatum(PG_DETOAST_DATUM(orig_val));
-	else
-		val = orig_val;
-
 	if (!PG_ARGISNULL(0) &&
 	  (tcategory == TYPCATEGORY_ARRAY || tcategory == TYPCATEGORY_COMPOSITE))
 	{
@@ -1749,10 +1707,6 @@ json_agg_transfn(PG_FUNCTION_ARGS)
 
 	datum_to_json(val, false, state, tcategory, typoutput);
 
-	/* Clean up detoasted copy, if any */
-	if (val != orig_val)
-		pfree(DatumGetPointer(val));
-
 	/*
 	 * The transition type for array_agg() is declared to be "internal", which
 	 * is a pass-by-value type the same size as a pointer.	So we can safely