[Tarantool-patches] [PATCH 03/14] WIP: module api/lua: add luaL_iscdata() function

[Alexander Turenko <alexander.turenko@tarantool.org>]

It is useful to provide a module specific error when cdata expected, but
a value of another type is passed.

Alternative would be using of lua_type() to check against LUA_TCDATA,
but this constant is not exposed for modules. See more in the
luaL_iscdata() API comment.

XXX: Add a test to test/app-tap/module_api.{c,test.lua}.

Part of #5273
---
 src/exports.h   |  1 +
 src/lua/utils.c |  6 ++++++
 src/lua/utils.h | 20 ++++++++++++++++++++
 3 files changed, 27 insertions(+)

diff --git a/src/exports.h b/src/exports.h
index 7861bb529..08ca03507 100644
--- a/src/exports.h
+++ b/src/exports.h
@@ -355,6 +355,7 @@ EXPORT(luaL_fileresult)
 EXPORT(luaL_findtable)
 EXPORT(luaL_getmetafield)
 EXPORT(luaL_gsub)
+EXPORT(luaL_iscdata)
 EXPORT(luaL_iscallable)
 EXPORT(luaL_loadbuffer)
 EXPORT(luaL_loadbufferx)
diff --git a/src/lua/utils.c b/src/lua/utils.c
index af114b0a2..bf5452d3e 100644
--- a/src/lua/utils.c
+++ b/src/lua/utils.c
@@ -112,6 +112,12 @@ luaL_pushuuid(struct lua_State *L)
 	return luaL_pushcdata(L, CTID_UUID);
 }
 
+int
+luaL_iscdata(struct lua_State *L, int idx)
+{
+	return lua_type(L, idx) == LUA_TCDATA;
+}
+
 void *
 luaL_checkcdata(struct lua_State *L, int idx, uint32_t *ctypeid)
 {
diff --git a/src/lua/utils.h b/src/lua/utils.h
index 7e02a05f2..e9dd27d08 100644
--- a/src/lua/utils.h
+++ b/src/lua/utils.h
@@ -78,6 +78,26 @@ luaL_pushuuid(struct lua_State *L);
 
 /** \cond public */
 
+/**
+ * @brief Checks whether a value on the Lua stack is a cdata.
+ *
+ * Unlike <luaL_checkcdata>() this function does not raise an
+ * error. It is useful to raise a domain specific error.
+ *
+ * Lua API and module API don't expose LUA_TCDATA constant.
+ * We have no guarantee that this constant will remain the same in
+ * future LuaJIT versions. So this function should be used in
+ * modules instead of `lua_type(L, idx) == LUA_TCDATA`.
+ *
+ * @param L Lua State
+ * @param idx stack index
+ *
+ * @return 1 if the value at the given acceptable index is a cdata
+ * and 0 otherwise.
+ */
+LUA_API int
+luaL_iscdata(struct lua_State *L, int idx);
+
 /**
  * @brief Push cdata of given \a ctypeid onto the stack.
  * CTypeID must be used from FFI at least once. Allocated memory returned
-- 
2.25.0