feat(util/lua): add helper functions for checking expected number of arguments in the Lua API

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

src/util/lua.cpp

@@ -195,5 +195,13 @@ lua_migrate_fn get_migrate_fn(lua_State * L, int i) {
     }
     return nullptr;
 }
+
+void check_num_args(lua_State * L, int num) {
+    if (lua_gettop(L) != num) throw exception("incorrect number of arguments in function application");
+}
+
+void check_atmost_num_args(lua_State * L, int high) {
+    if (lua_gettop(L) > high) throw exception("too many arguments in function application");
+}
 }
 

src/util/lua.h

@@ -64,12 +64,9 @@ DECL_PUSH_CORE(T, T, T &&)
 
 #define DECL_GC(T) static int T ## _gc(lua_State * L) { static_cast<T*>(lua_touserdata(L, 1))->~T(); return 0; }
 
-#define DECL_PRED(T)                                                     \
+#define DECL_PRED(T)                                                    \
 bool is_ ## T(lua_State * L, int idx) { return testudata(L, idx, T ## _mt); } \
-static int T ## _pred(lua_State * L) {                                  \
-    lua_pushboolean(L, is_ ## T(L, 1));                                 \
-    return 1;                                                           \
-}
+static int T ## _pred(lua_State * L) { check_num_args(L, 1); return push_boolean(L, is_ ## T(L, 1)); }
 
 void throw_bad_arg_error(lua_State * L, int i, char const * expected_type);
 
@@ -138,4 +135,13 @@ inline int push_integer(lua_State * L, lua_Integer v) { lua_pushinteger(L, v); r
 inline int push_number(lua_State * L, lua_Number v) { lua_pushnumber(L, v); return 1; }
 inline int push_nil(lua_State * L) { lua_pushnil(L); return 1; }
 // =======================================
+
+// =======================================
+// Extra validation functions
+
+/** \brief Throw an exception if lua_gettop(L) != num */
+void check_num_args(lua_State * L, int num);
+/** \brief Throw an exception if lua_gettop(L) > high */
+void check_atmost_num_args(lua_State * L, int high);
+// =======================================
 }

src/util/name.cpp

@@ -530,7 +530,7 @@ static int name_tostring(lua_State * L) { return push_string(L, to_name(L, 1).to
 static int name_eq(lua_State * L) { return push_boolean(L, to_name(L, 1) == to_name(L, 2)); }
 static int name_lt(lua_State * L) { return push_boolean(L, to_name(L, 1) < to_name(L, 2)); }
 static int name_hash(lua_State * L) { return push_integer(L, to_name(L, 1).hash()); }
-#define NAME_PRED(P) static int name_ ## P(lua_State * L) { return push_boolean(L, to_name(L, 1).P()); }
+#define NAME_PRED(P) static int name_ ## P(lua_State * L) { check_num_args(L, 1); return push_boolean(L, to_name(L, 1).P()); }
 NAME_PRED(is_atomic)
 NAME_PRED(is_anonymous)
 NAME_PRED(is_string)

src/util/sexpr/sexpr.cpp

@@ -408,7 +408,7 @@ static int mk_sexpr(lua_State * L) {
 static int sexpr_eq(lua_State * L)        { return push_boolean(L, to_sexpr(L, 1) == to_sexpr(L, 2)); }
 static int sexpr_lt(lua_State * L)        { return push_boolean(L, to_sexpr(L, 1) < to_sexpr(L, 2)); }
 
-#define SEXPR_PRED(P) static int sexpr_ ## P(lua_State * L) { return push_boolean(L, P(to_sexpr(L, 1))); }
+#define SEXPR_PRED(P) static int sexpr_ ## P(lua_State * L) { check_num_args(L, 1); return push_boolean(L, P(to_sexpr(L, 1))); }
 
 SEXPR_PRED(is_nil)
 SEXPR_PRED(is_cons)