tests/capi: support floor division operation

The PUC Rio Lua 5.3 has introduced a floor division (//)
operation. It is a division that rounds the quotient towards
minus infinity, that is, the floor of the division of its operands.
The patch adds support of the aforementioned operation to a
protobuf schema, serializer and preamble.

Author: ligurio

tests/capi/luaL_loadbuffer_proto/lua_grammar.proto

@@ -383,6 +383,9 @@ message BinaryOperator {
         uint32 notEqual = 13;
         uint32 and = 14;
         uint32 or = 15;
+
+        /* Arithmetic operators (5.3+). */
+        uint32 idiv = 16;
     }
 }
 

tests/capi/luaL_loadbuffer_proto/preamble.lua

@@ -8,6 +8,8 @@ local not_nan_and_nil = function(val)
     return (val ~= val or val == nil) and DEFAULT_NUMBER or val
 end
 
+_G.always_number = always_number
+
 local __add = function(v1, v2)
     return always_number(v1) + always_number(v2)
 end
@@ -70,11 +72,16 @@ end
 local __unm = function(v)
     return - always_number(v)
 end
+local __idiv = load([[
+    local v1, v2 = ...
+    return always_number(v1) // always_number(v2)
+]])
 
 debug.setmetatable('string', {
     __add = __add,
     __call = __call,
     __div = __div,
+    __idiv = __idiv,
     __index = __index,
     __mod = __mod,
     __mul = __mul,
@@ -88,6 +95,7 @@ debug.setmetatable(0, {
     __call = __call,
     __concat = __concat,
     __div = __div,
+    __idiv = __idiv,
     __index = __index,
     __len = __len,
     __newindex = __newindex,
@@ -97,6 +105,7 @@ debug.setmetatable(nil, {
     __call = __call,
     __concat = __concat,
     __div = __div,
+    __idiv = __idiv,
     __index = __index,
     __le = __le,
     __len = __len,
@@ -112,6 +121,7 @@ debug.setmetatable(function() end, {
     __add = __add,
     __concat = __concat,
     __div = __div,
+    __idiv = __idiv,
     __index = __index,
     __le = __le,
     __len = __len,
@@ -128,6 +138,7 @@ debug.setmetatable(true, {
     __call = __call,
     __concat = __concat,
     __div = __div,
+    __idiv = __idiv,
     __index = __index,
     __le = __le,
     __len = __len,
@@ -144,6 +155,7 @@ local table_mt = {
     __call = __call,
     __concat = __concat,
     __div = __div,
+    __idiv = __idiv,
     __le = __le,
     __len = __len,
     __lt = __lt,

tests/capi/luaL_loadbuffer_proto/serializer.cc

@@ -1157,6 +1157,10 @@ PROTO_TOSTRING(BinaryOperator, op)
 		return "*";
 	case BinopType::kDiv:
 		return "/";
+#if LUA_VERSION_NUM >= 503
+	case BinopType::kIDiv:
+		return "//";
+#endif
 	case BinopType::kExp:
 		return "^";
 	case BinopType::kMod: