Process variadic arguments consistently in json functions

json_build_object and json_build_array and the jsonb equivalents did not
correctly process explicit VARIADIC arguments. They are modified to use
the new extract_variadic_args() utility function which abstracts away
the details of the call method.

Michael Paquier, reviewed by Tom Lane and Dmitry Dolgov.

Backpatch to 9.5 for the jsonb fixes and 9.4 for the json fixes, as
that's where they originated.

Author: adunstan

src/backend/utils/adt/json.c

@@ -17,6 +17,7 @@
 #include "access/transam.h"
 #include "catalog/pg_type.h"
 #include "executor/spi.h"
+#include "funcapi.h"
 #include "lib/stringinfo.h"
 #include "libpq/pqformat.h"
 #include "mb/pg_wchar.h"
@@ -2111,10 +2112,17 @@ json_build_object(PG_FUNCTION_ARGS)
 {
 	int			nargs = PG_NARGS();
 	int			i;
-	Datum		arg;
 	const char *sep = "";
 	StringInfo	result;
-	Oid			val_type;
+	Datum	   *args;
+	bool	   *nulls;
+	Oid		   *types;
+
+	/* fetch argument values to build the object */
+	nargs = extract_variadic_args(fcinfo, 0, false, &args, &types, &nulls);
+
+	if (nargs < 0)
+		PG_RETURN_NULL();
 
 	if (nargs % 2 != 0)
 		ereport(ERROR,
@@ -2128,52 +2136,22 @@ json_build_object(PG_FUNCTION_ARGS)
 
 	for (i = 0; i < nargs; i += 2)
 	{
-		/*
-		 * Note: since json_build_object() is declared as taking type "any",
-		 * the parser will not do any type conversion on unknown-type literals
-		 * (that is, undecorated strings or NULLs).  Such values will arrive
-		 * here as type UNKNOWN, which fortunately does not matter to us,
-		 * since unknownout() works fine.
-		 */
 		appendStringInfoString(result, sep);
 		sep = ", ";
 
 		/* process key */
-		val_type = get_fn_expr_argtype(fcinfo->flinfo, i);
-
-		if (val_type == InvalidOid)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("could not determine data type for argument %d",
-							i + 1)));
-
-		if (PG_ARGISNULL(i))
+		if (nulls[i])
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 					 errmsg("argument %d cannot be null", i + 1),
 					 errhint("Object keys should be text.")));
 
-		arg = PG_GETARG_DATUM(i);
-
-		add_json(arg, false, result, val_type, true);
+		add_json(args[i], false, result, types[i], true);
 
 		appendStringInfoString(result, " : ");
 
 		/* process value */
-		val_type = get_fn_expr_argtype(fcinfo->flinfo, i + 1);
-
-		if (val_type == InvalidOid)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("could not determine data type for argument %d",
-							i + 2)));
-
-		if (PG_ARGISNULL(i + 1))
-			arg = (Datum) 0;
-		else
-			arg = PG_GETARG_DATUM(i + 1);
-
-		add_json(arg, PG_ARGISNULL(i + 1), result, val_type, false);
+		add_json(args[i + 1], nulls[i + 1], result, types[i + 1], false);
 	}
 
 	appendStringInfoChar(result, '}');
@@ -2196,43 +2174,29 @@ json_build_object_noargs(PG_FUNCTION_ARGS)
 Datum
 json_build_array(PG_FUNCTION_ARGS)
 {
-	int			nargs = PG_NARGS();
+	int			nargs;
 	int			i;
-	Datum		arg;
 	const char *sep = "";
 	StringInfo	result;
-	Oid			val_type;
+	Datum	   *args;
+	bool	   *nulls;
+	Oid		   *types;
+
+	/* fetch argument values to build the array */
+	nargs = extract_variadic_args(fcinfo, 0, false, &args, &types, &nulls);
+
+	if (nargs < 0)
+		PG_RETURN_NULL();
 
 	result = makeStringInfo();
 
 	appendStringInfoChar(result, '[');
 
 	for (i = 0; i < nargs; i++)
 	{
-		/*
-		 * Note: since json_build_array() is declared as taking type "any",
-		 * the parser will not do any type conversion on unknown-type literals
-		 * (that is, undecorated strings or NULLs).  Such values will arrive
-		 * here as type UNKNOWN, which fortunately does not matter to us,
-		 * since unknownout() works fine.
-		 */
 		appendStringInfoString(result, sep);
 		sep = ", ";
-
-		val_type = get_fn_expr_argtype(fcinfo->flinfo, i);
-
-		if (val_type == InvalidOid)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("could not determine data type for argument %d",
-							i + 1)));
-
-		if (PG_ARGISNULL(i))
-			arg = (Datum) 0;
-		else
-			arg = PG_GETARG_DATUM(i);
-
-		add_json(arg, PG_ARGISNULL(i), result, val_type, false);
+		add_json(args[i], nulls[i], result, types[i], false);
 	}
 
 	appendStringInfoChar(result, ']');

src/backend/utils/adt/jsonb.c

@@ -3,7 +3,7 @@
  * jsonb.c
  *		I/O routines for jsonb type
  *
- * Copyright (c) 2014-2017, PostgreSQL Global Development Group
+ * COPYRIGHT (c) 2014-2017, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
  *	  src/backend/utils/adt/jsonb.c
@@ -16,6 +16,7 @@
 #include "access/htup_details.h"
 #include "access/transam.h"
 #include "catalog/pg_type.h"
+#include "funcapi.h"
 #include "libpq/pqformat.h"
 #include "parser/parse_coerce.h"
 #include "utils/builtins.h"
@@ -1171,16 +1172,24 @@ to_jsonb(PG_FUNCTION_ARGS)
 Datum
 jsonb_build_object(PG_FUNCTION_ARGS)
 {
-	int			nargs = PG_NARGS();
+	int			nargs;
 	int			i;
-	Datum		arg;
-	Oid			val_type;
 	JsonbInState result;
+	Datum	   *args;
+	bool	   *nulls;
+	Oid		   *types;
+
+	/* build argument values to build the object */
+	nargs = extract_variadic_args(fcinfo, 0, true, &args, &types, &nulls);
+
+	if (nargs < 0)
+		PG_RETURN_NULL();
 
 	if (nargs % 2 != 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("invalid number of arguments: object must be matched key value pairs")));
+				 errmsg("argument list must have even number of elements"),
+				 errhint("The arguments of jsonb_build_object() must consist of alternating keys and values.")));
 
 	memset(&result, 0, sizeof(JsonbInState));
 
@@ -1189,54 +1198,15 @@ jsonb_build_object(PG_FUNCTION_ARGS)
 	for (i = 0; i < nargs; i += 2)
 	{
 		/* process key */
-
-		if (PG_ARGISNULL(i))
+		if (nulls[i])
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 					 errmsg("argument %d: key must not be null", i + 1)));
-		val_type = get_fn_expr_argtype(fcinfo->flinfo, i);
-
-		/*
-		 * turn a constant (more or less literal) value that's of unknown type
-		 * into text. Unknowns come in as a cstring pointer.
-		 */
-		if (val_type == UNKNOWNOID && get_fn_expr_arg_stable(fcinfo->flinfo, i))
-		{
-			val_type = TEXTOID;
-			arg = CStringGetTextDatum(PG_GETARG_POINTER(i));
-		}
-		else
-		{
-			arg = PG_GETARG_DATUM(i);
-		}
-		if (val_type == InvalidOid || val_type == UNKNOWNOID)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("could not determine data type for argument %d", i + 1)));
 
-		add_jsonb(arg, false, &result, val_type, true);
+		add_jsonb(args[i], false, &result, types[i], true);
 
 		/* process value */
-
-		val_type = get_fn_expr_argtype(fcinfo->flinfo, i + 1);
-		/* see comments above */
-		if (val_type == UNKNOWNOID && get_fn_expr_arg_stable(fcinfo->flinfo, i + 1))
-		{
-			val_type = TEXTOID;
-			if (PG_ARGISNULL(i + 1))
-				arg = (Datum) 0;
-			else
-				arg = CStringGetTextDatum(PG_GETARG_POINTER(i + 1));
-		}
-		else
-		{
-			arg = PG_GETARG_DATUM(i + 1);
-		}
-		if (val_type == InvalidOid || val_type == UNKNOWNOID)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("could not determine data type for argument %d", i + 2)));
-		add_jsonb(arg, PG_ARGISNULL(i + 1), &result, val_type, false);
+		add_jsonb(args[i + 1], nulls[i + 1], &result, types[i + 1], false);
 	}
 
 	result.res = pushJsonbValue(&result.parseState, WJB_END_OBJECT, NULL);
@@ -1266,38 +1236,25 @@ jsonb_build_object_noargs(PG_FUNCTION_ARGS)
 Datum
 jsonb_build_array(PG_FUNCTION_ARGS)
 {
-	int			nargs = PG_NARGS();
+	int			nargs;
 	int			i;
-	Datum		arg;
-	Oid			val_type;
 	JsonbInState result;
+	Datum	   *args;
+	bool	   *nulls;
+	Oid		   *types;
+
+	/* build argument values to build the array */
+	nargs = extract_variadic_args(fcinfo, 0, true, &args, &types, &nulls);
+
+	if (nargs < 0)
+		PG_RETURN_NULL();
 
 	memset(&result, 0, sizeof(JsonbInState));
 
 	result.res = pushJsonbValue(&result.parseState, WJB_BEGIN_ARRAY, NULL);
 
 	for (i = 0; i < nargs; i++)
-	{
-		val_type = get_fn_expr_argtype(fcinfo->flinfo, i);
-		/* see comments in jsonb_build_object above */
-		if (val_type == UNKNOWNOID && get_fn_expr_arg_stable(fcinfo->flinfo, i))
-		{
-			val_type = TEXTOID;
-			if (PG_ARGISNULL(i))
-				arg = (Datum) 0;
-			else
-				arg = CStringGetTextDatum(PG_GETARG_POINTER(i));
-		}
-		else
-		{
-			arg = PG_GETARG_DATUM(i);
-		}
-		if (val_type == InvalidOid || val_type == UNKNOWNOID)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("could not determine data type for argument %d", i + 1)));
-		add_jsonb(arg, PG_ARGISNULL(i), &result, val_type, false);
-	}
+		add_jsonb(args[i], nulls[i], &result, types[i], false);
 
 	result.res = pushJsonbValue(&result.parseState, WJB_END_ARRAY, NULL);