[PATCH 1/3] Add luaT_iscallable with support of cdata metatype

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

Needed for #3276.
---
 extra/exports                    |  1 +
 src/lua/utils.c                  | 43 ++++++++++++++++
 src/lua/utils.h                  | 10 ++++
 test/app-tap/module_api.c        | 10 ++++
 test/app-tap/module_api.test.lua | 85 +++++++++++++++++++++++++++++++-
 5 files changed, 147 insertions(+), 2 deletions(-)

diff --git a/extra/exports b/extra/exports
index 5f69e0730..52f0b2378 100644
--- a/extra/exports
+++ b/extra/exports
@@ -134,6 +134,7 @@ luaT_call
 luaT_cpcall
 luaT_state
 luaT_tolstring
+luaT_iscallable
 box_txn
 box_txn_begin
 box_txn_commit
diff --git a/src/lua/utils.c b/src/lua/utils.c
index 978fe61f1..7a6069fbb 100644
--- a/src/lua/utils.c
+++ b/src/lua/utils.c
@@ -920,6 +920,49 @@ luaT_tolstring(lua_State *L, int idx, size_t *len)
 	return lua_tolstring(L, -1, len);
 }
 
+/* Based on ffi_meta___call() from luajit/src/lib_ffi.c. */
+static int
+luaT_cdata_iscallable(lua_State *L, int idx)
+{
+	/* Calculate absolute value in the stack. */
+	if (idx < 0)
+		idx = lua_gettop(L) + idx + 1;
+
+	/* Get cdata from the stack. */
+	assert(lua_type(L, idx) == LUA_TCDATA);
+	GCcdata *cd = cdataV(L->base + idx - 1);
+
+	CTState *cts = ctype_cts(L);
+	CTypeID id = cd->ctypeid;
+	CType *ct = ctype_raw(cts, id);
+	if (ctype_isptr(ct->info))
+		id = ctype_cid(ct->info);
+
+	/* Get ctype metamethod. */
+	cTValue *tv = lj_ctype_meta(cts, id, MM_call);
+
+	return tv != NULL;
+}
+
+int
+luaT_iscallable(lua_State *L, int idx)
+{
+	/* Whether it is function. */
+	int res = lua_isfunction(L, idx);
+	if (res == 1)
+		return 1;
+
+	/* Whether it is cdata with metatype with __call field. */
+	if (lua_type(L, idx) == LUA_TCDATA)
+		return luaT_cdata_iscallable(L, idx);
+
+	/* Whether it has metatable with __call field. */
+	res = luaL_getmetafield(L, idx, "__call");
+	if (res == 1)
+		lua_pop(L, 1); /* Pop __call value. */
+	return res;
+}
+
 lua_State *
 luaT_state(void)
 {
diff --git a/src/lua/utils.h b/src/lua/utils.h
index a47e3d2b4..b62327217 100644
--- a/src/lua/utils.h
+++ b/src/lua/utils.h
@@ -438,6 +438,16 @@ luaT_state(void);
 LUA_API const char *
 luaT_tolstring(lua_State *L, int idx, size_t *ssize);
 
+/**
+ * Check whether a Lua object is a function or has
+ * metatable/metatype with a __call field.
+ *
+ * Note: It does not check type of __call metatable/metatype
+ * field.
+ */
+LUA_API int
+luaT_iscallable(lua_State *L, int idx);
+
 /** \endcond public */
 
 /**
diff --git a/test/app-tap/module_api.c b/test/app-tap/module_api.c
index 4abe1af48..ef0c292e8 100644
--- a/test/app-tap/module_api.c
+++ b/test/app-tap/module_api.c
@@ -440,6 +440,15 @@ test_tostring(lua_State *L)
 	return 1;
 }
 
+static int
+test_iscallable(lua_State *L)
+{
+	int exp = lua_toboolean(L, 2);
+	int res = luaT_iscallable(L, 1);
+	lua_pushboolean(L, res == exp);
+	return 1;
+}
+
 LUA_API int
 luaopen_module_api(lua_State *L)
 {
@@ -467,6 +476,7 @@ luaopen_module_api(lua_State *L)
 		{"test_cpcall", test_cpcall},
 		{"test_state", test_state},
 		{"test_tostring", test_tostring},
+		{"iscallable", test_iscallable},
 		{NULL, NULL}
 	};
 	luaL_register(L, "module_api", lib);
diff --git a/test/app-tap/module_api.test.lua b/test/app-tap/module_api.test.lua
index f93257236..a6658cc61 100755
--- a/test/app-tap/module_api.test.lua
+++ b/test/app-tap/module_api.test.lua
@@ -3,7 +3,9 @@
 local fio = require('fio')
 
 box.cfg{log = "tarantool.log"}
-build_path = os.getenv("BUILDDIR")
+-- Use BUILDDIR passed from test-run or cwd when run w/o
+-- test-run to find test/app-tap/module_api.{so,dylib}.
+build_path = os.getenv("BUILDDIR") or '.'
 package.cpath = fio.pathjoin(build_path, 'test/app-tap/?.so'   ) .. ';' ..
                 fio.pathjoin(build_path, 'test/app-tap/?.dylib') .. ';' ..
                 package.cpath
@@ -36,8 +38,86 @@ local function test_pushcdata(test, module)
     test:is(gc_counter, 1, 'pushcdata gc')
 end
 
+local function test_iscallable(test, module)
+    local ffi = require('ffi')
+
+    ffi.cdef([[
+        struct cdata_1 { int foo; };
+        struct cdata_2 { int foo; };
+    ]])
+
+    local cdata_1 = ffi.new('struct cdata_1')
+    local cdata_1_ref = ffi.new('struct cdata_1 &')
+    local cdata_2 = ffi.new('struct cdata_2')
+    local cdata_2_ref = ffi.new('struct cdata_2 &')
+
+    local nop = function() end
+
+    ffi.metatype('struct cdata_2', {
+        __call = nop,
+    })
+
+    local cases = {
+        {
+            obj = nop,
+            exp = true,
+            description = 'function',
+        },
+        {
+            obj = nil,
+            exp = false,
+            description = 'nil',
+        },
+        {
+            obj = 1,
+            exp = false,
+            description = 'number',
+        },
+        {
+            obj = {},
+            exp = false,
+            description = 'table without metatable',
+        },
+        {
+            obj = setmetatable({}, {}),
+            exp = false,
+            description = 'table without __call metatable field',
+        },
+        {
+            obj = setmetatable({}, {__call = nop}),
+            exp = true,
+            description = 'table with __call metatable field'
+        },
+        {
+            obj = cdata_1,
+            exp = false,
+            description = 'cdata without __call metatable field',
+        },
+        {
+            obj = cdata_1_ref,
+            exp = false,
+            description = 'cdata reference without __call metatable field',
+        },
+        {
+            obj = cdata_2,
+            exp = true,
+            description = 'cdata with __call metatable field',
+        },
+        {
+            obj = cdata_2_ref,
+            exp = true,
+            description = 'cdata reference with __call metatable field',
+        },
+    }
+
+    test:plan(#cases)
+    for _, case in ipairs(cases) do
+        test:ok(module.iscallable(case.obj, case.exp), case.description)
+    end
+end
+
 local test = require('tap').test("module_api", function(test)
-    test:plan(23)
+    test:plan(24)
     local status, module = pcall(require, 'module_api')
     test:is(status, true, "module")
     test:ok(status, "module is loaded")
@@ -62,6 +142,7 @@ local test = require('tap').test("module_api", function(test)
     test:like(msg, 'luaT_error', 'luaT_error')
 
     test:test("pushcdata", test_pushcdata, module)
+    test:test("iscallable", test_iscallable, module)
 
     space:drop()
 end)
-- 
2.19.2