A fix and a test case for gh-300

A fix and a test case for gh-300: misleading error message for a
non-existing function.

First, check that a function exists. Then check access rights
to the function.

src/box/lua/call.cc

@@ -516,10 +516,16 @@ box_lua_call(struct request *request, struct txn *txn, struct port *port)
 	uint32_t name_len = mp_decode_strl(&name);
 
 	uint8_t access = PRIV_X & ~user->universal_access;
-	access_check_func(name, name_len, user, access);
 
-	/* proc name */
+	/* Try to find a function by name */
 	int oc = box_lua_find(L, name, name + name_len);
+	/**
+	 * Check access to the function. Sic: the order
+	 * is important, as is described in
+	 * https://github.com/tarantool/tarantool/issues/300
+	 * - if a function does not exist, say it first.
+	 */
+	access_check_func(name, name_len, user, access);
 	/* Push the rest of args (a tuple). */
 	const char *args = request->tuple;
 	uint32_t arg_count = mp_decode_array(&args);

test/box/access.result

@@ -158,3 +158,29 @@ box.schema.user.create('Петя_Иванов')
 box.schema.user.drop('Петя_Иванов')
 ---
 ...
+-- gh-300: misleading error message if a function does not exist
+c = box.net.box.new("localhost", box.cfg.primary_port)
+---
+...
+c:call('nosuchfunction')
+---
+- error: Procedure 'nosuchfunction' is not defined
+...
+function nosuchfunction() end
+---
+...
+c:call('nosuchfunction')
+---
+- error: Execute access denied for user 'guest' to function 'nosuchfunction'
+...
+nosuchfunction = nil
+---
+...
+c:call('nosuchfunction')
+---
+- error: Procedure 'nosuchfunction' is not defined
+...
+c:close()
+---
+- true
+...

test/box/access.test.lua

@@ -72,3 +72,12 @@ box.schema.user.create(' ')
 -- valid identifiers
 box.schema.user.create('Петя_Иванов')
 box.schema.user.drop('Петя_Иванов')
+
+-- gh-300: misleading error message if a function does not exist
+c = box.net.box.new("localhost", box.cfg.primary_port)
+c:call('nosuchfunction')
+function nosuchfunction() end
+c:call('nosuchfunction')
+nosuchfunction = nil
+c:call('nosuchfunction')
+c:close()