lua: Add ability to pass tables with __call

vim-patch:8.2.1054: not so easy to pass a lua function to Vim
vim-patch:8.2.1084: Lua: registering function has useless code

I think I have also opened up the possibility for people to use these
callbacks elsewhere, since I've added a new struct that we should be
able to use.

Also, this should allow us to determine what the state of a list is in
Lua or a dictionary in Lua, since we now can track the luaref as we go.

9 files changed, 268 insertions, 50 deletions

diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 27c2ed1ea5..e1f9fe0253 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -7143,6 +7143,16 @@ bool callback_from_typval(Callback *const callback, typval_T *const arg)
     func_ref(name);
     callback->data.funcref = vim_strsave(name);
     callback->type = kCallbackFuncref;
+  } else if (nlua_is_table_from_lua(arg)) {
+    char_u *name = nlua_register_table_as_callable(arg);
+
+    if (name != NULL) {
+      func_ref(name);
+      callback->data.funcref = vim_strsave(name);
+      callback->type = kCallbackFuncref;
+    } else {
+      r = FAIL;
+    }
   } else if (arg->v_type == VAR_NUMBER && arg->vval.v_number == 0) {
     callback->type = kCallbackNone;
   } else {
diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index 1071e75c06..99014d1a09 100644
--- a/src/nvim/eval/funcs.c
+++ b/src/nvim/eval/funcs.c
@@ -824,9 +824,12 @@ static void f_call(typval_T *argvars, typval_T *rettv, FunPtr fptr)
   } else if (argvars[0].v_type == VAR_PARTIAL) {
     partial = argvars[0].vval.v_partial;
     func = partial_name(partial);
+  } else if (nlua_is_table_from_lua(&argvars[0])) {
+    func = nlua_register_table_as_callable(&argvars[0]);
   } else {
     func = (char_u *)tv_get_string(&argvars[0]);
   }
+
   if (*func == NUL) {
     return;             // type error or empty name
   }
diff --git a/src/nvim/eval/typval.c b/src/nvim/eval/typval.c
index 0daaf6c878..89ca2db59b 100644
--- a/src/nvim/eval/typval.c
+++ b/src/nvim/eval/typval.c
@@ -16,6 +16,7 @@
 #include "nvim/eval/typval_encode.h"
 #include "nvim/eval.h"
 #include "nvim/eval/userfunc.h"
+#include "nvim/lua/executor.h"
 #include "nvim/types.h"
 #include "nvim/assert.h"
 #include "nvim/memory.h"
@@ -301,6 +302,7 @@ void tv_list_free_list(list_T *const l)
   }
   list_log(l, NULL, NULL, "freelist");
 
+  nlua_free_typval_list(l);
   xfree(l);
 }
 
@@ -1374,6 +1376,7 @@ void tv_dict_free_dict(dict_T *const d)
     d->dv_used_next->dv_used_prev = d->dv_used_prev;
   }
 
+  nlua_free_typval_dict(d);
   xfree(d);
 }
 
diff --git a/src/nvim/eval/typval.h b/src/nvim/eval/typval.h
index cb13bec50d..503a32a81e 100644
--- a/src/nvim/eval/typval.h
+++ b/src/nvim/eval/typval.h
@@ -180,6 +180,8 @@ struct listvar_S {
   int lv_idx;  ///< Index of a cached item, used for optimising repeated l[idx].
   int lv_copyID;  ///< ID used by deepcopy().
   VarLockStatus lv_lock;  ///< Zero, VAR_LOCKED, VAR_FIXED.
+
+  LuaRef lua_table_ref;
 };
 
 // Static list with 10 items. Use tv_list_init_static10() to initialize.
@@ -245,6 +247,8 @@ struct dictvar_S {
   dict_T *dv_used_next;   ///< Next dictionary in used dictionaries list.
   dict_T *dv_used_prev;   ///< Previous dictionary in used dictionaries list.
   QUEUE watchers;         ///< Dictionary key watchers set by user code.
+
+  LuaRef lua_table_ref;
 };
 
 /// Type used for script ID
@@ -271,9 +275,10 @@ typedef struct {
 /// Number of fixed variables used for arguments
 #define FIXVAR_CNT 12
 
-/// Callback interface for C function reference
+/// Callback interface for C function reference>
+///     Used for managing functions that were registered with |register_cfunc|
 typedef int (*cfunc_T)(int argcount, typval_T *argvars, typval_T *rettv, void *state);  // NOLINT
-/// Callback to clear cfunc_T
+/// Callback to clear cfunc_T and any associated state.
 typedef void (*cfunc_free_T)(void *state);
 
 // Structure to hold info for a function that is currently being executed.
diff --git a/src/nvim/eval/userfunc.c b/src/nvim/eval/userfunc.c
index ca2f4a32ca..229f0e8dde 100644
--- a/src/nvim/eval/userfunc.c
+++ b/src/nvim/eval/userfunc.c
@@ -3458,7 +3458,6 @@ char_u *register_cfunc(cfunc_T cb, cfunc_free_T cb_free, void *state)
 {
   char_u *name = get_lambda_name();
   ufunc_T *fp = NULL;
-  int flags = FC_CFUNC;
 
   fp = xcalloc(1, offsetof(ufunc_T, uf_name) + STRLEN(name) + 1);
   if (fp == NULL) {
@@ -3467,7 +3466,7 @@ char_u *register_cfunc(cfunc_T cb, cfunc_free_T cb_free, void *state)
 
   fp->uf_refcount = 1;
   fp->uf_varargs = true;
-  fp->uf_flags = flags;
+  fp->uf_flags = FC_CFUNC;
   fp->uf_calls = 0;
   fp->uf_script_ctx = current_sctx;
   fp->uf_cb = cb;
@@ -3477,5 +3476,5 @@ char_u *register_cfunc(cfunc_T cb, cfunc_free_T cb_free, void *state)
   STRCPY(fp->uf_name, name);
   hash_add(&func_hashtab, UF2HIKEY(fp));
 
-  return name;
+  return fp->uf_name;
 }
diff --git a/src/nvim/lua/converter.c b/src/nvim/lua/converter.c
index 9fc4ca7e7e..32e804d213 100644
--- a/src/nvim/lua/converter.c
+++ b/src/nvim/lua/converter.c
@@ -316,6 +316,13 @@ bool nlua_pop_typval(lua_State *lstate, typval_T *ret_tv)
         break;
       }
       case LUA_TTABLE: {
+        // Only need to track table refs if we have a metatable associated.
+        LuaRef table_ref = LUA_NOREF;
+        if (lua_getmetatable(lstate, -1)) {
+          lua_pop(lstate, 1);
+          table_ref = nlua_ref(lstate, -1);
+        }
+
         const LuaTableProps table_props = nlua_traverse_table(lstate);
 
         for (size_t i = 0; i < kv_size(stack); i++) {
@@ -331,6 +338,7 @@ bool nlua_pop_typval(lua_State *lstate, typval_T *ret_tv)
           case kObjectTypeArray: {
             cur.tv->v_type = VAR_LIST;
             cur.tv->vval.v_list = tv_list_alloc((ptrdiff_t)table_props.maxidx);
+            cur.tv->vval.v_list->lua_table_ref = table_ref;
             tv_list_ref(cur.tv->vval.v_list);
             if (table_props.maxidx != 0) {
               cur.container = true;
@@ -344,6 +352,7 @@ bool nlua_pop_typval(lua_State *lstate, typval_T *ret_tv)
               cur.tv->v_type = VAR_DICT;
               cur.tv->vval.v_dict = tv_dict_alloc();
               cur.tv->vval.v_dict->dv_refcount++;
+              cur.tv->vval.v_dict->lua_table_ref = table_ref;
             } else {
               cur.special = table_props.has_string_with_nul;
               if (table_props.has_string_with_nul) {
@@ -354,11 +363,13 @@ bool nlua_pop_typval(lua_State *lstate, typval_T *ret_tv)
                                                         S_LEN("_VAL"));
                 assert(val_di != NULL);
                 cur.tv = &val_di->di_tv;
+                cur.tv->vval.v_list->lua_table_ref = table_ref;
                 assert(cur.tv->v_type == VAR_LIST);
               } else {
                 cur.tv->v_type = VAR_DICT;
                 cur.tv->vval.v_dict = tv_dict_alloc();
                 cur.tv->vval.v_dict->dv_refcount++;
+                cur.tv->vval.v_dict->lua_table_ref = table_ref;
               }
               cur.container = true;
               cur.idx = lua_gettop(lstate);
@@ -388,8 +399,8 @@ nlua_pop_typval_table_processing_end:
       }
       case LUA_TFUNCTION: {
         LuaCFunctionState *state = xmalloc(sizeof(LuaCFunctionState));
-
         state->lua_callable.func_ref = nlua_ref(lstate, -1);
+        state->lua_callable.table_ref = LUA_NOREF;
 
         char_u *name = register_cfunc(
             &nlua_CFunction_func_call,
diff --git a/src/nvim/lua/converter.h b/src/nvim/lua/converter.h
index e74e3fb084..8601a32418 100644
--- a/src/nvim/lua/converter.h
+++ b/src/nvim/lua/converter.h
@@ -10,11 +10,12 @@
 #include "nvim/eval.h"
 
 typedef struct {
-    LuaRef func_ref;
+  LuaRef func_ref;
+  LuaRef table_ref;
 } LuaCallable;
 
 typedef struct {
-    LuaCallable lua_callable;
+  LuaCallable lua_callable;
 } LuaCFunctionState;
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
diff --git a/src/nvim/lua/executor.c b/src/nvim/lua/executor.c
index 5e924a9f90..9f30609d66 100644
--- a/src/nvim/lua/executor.c
+++ b/src/nvim/lua/executor.c
@@ -53,6 +53,15 @@ typedef struct {
 # include "lua/executor.c.generated.h"
 #endif
 
+#define PUSH_ALL_TYPVALS(lstate, args, argcount, special) \
+  for (int i = 0; i < argcount; i++) { \
+    if (args[i].v_type == VAR_UNKNOWN) { \
+      lua_pushnil(lstate); \
+    } else { \
+      nlua_push_typval(lstate, &args[i], special); \
+    } \
+  }
+
 /// Convert lua error into a Vim error message
 ///
 /// @param  lstate  Lua interpreter state.
@@ -700,24 +709,25 @@ int nlua_call(lua_State *lstate)
   }
 
   TRY_WRAP({
-  // TODO(bfredl): this should be simplified in error handling refactor
-  force_abort = false;
-  suppress_errthrow = false;
-  current_exception = NULL;
-  did_emsg = false;
-
-  try_start();
-  typval_T rettv;
-  int dummy;
-  // call_func() retval is deceptive, ignore it.  Instead we set `msg_list`
-  // (TRY_WRAP) to capture abort-causing non-exception errors.
-  (void)call_func(name, (int)name_len, &rettv, nargs,
-                  vim_args, NULL, curwin->w_cursor.lnum, curwin->w_cursor.lnum,
-                  &dummy, true, NULL, NULL);
-  if (!try_end(&err)) {
-    nlua_push_typval(lstate, &rettv, false);
-  }
-  tv_clear(&rettv);
+    // TODO(bfredl): this should be simplified in error handling refactor
+    force_abort = false;
+    suppress_errthrow = false;
+    current_exception = NULL;
+    did_emsg = false;
+
+    try_start();
+    typval_T rettv;
+    int dummy;
+    // call_func() retval is deceptive, ignore it.  Instead we set `msg_list`
+    // (TRY_WRAP) to capture abort-causing non-exception errors.
+    (void)call_func(name, (int)name_len, &rettv, nargs,
+                    vim_args, NULL,
+                    curwin->w_cursor.lnum, curwin->w_cursor.lnum,
+                    &dummy, true, NULL, NULL);
+    if (!try_end(&err)) {
+      nlua_push_typval(lstate, &rettv, false);
+    }
+    tv_clear(&rettv);
   });
 
 free_vim_args:
@@ -839,6 +849,19 @@ void nlua_pushref(lua_State *lstate, LuaRef ref)
   lua_rawgeti(lstate, LUA_REGISTRYINDEX, ref);
 }
 
+/// Gets a new reference to an object stored at original_ref
+///
+/// NOTE: It does not copy the value, it creates a new ref to the lua object.
+///       Leaves the stack unchanged.
+LuaRef nlua_newref(lua_State *lstate, LuaRef original_ref)
+{
+  nlua_pushref(lstate, original_ref);
+  LuaRef new_ref = nlua_ref(lstate, -1);
+  lua_pop(lstate, 1);
+
+  return new_ref;
+}
+
 /// Evaluate lua string
 ///
 /// Used for luaeval().
@@ -916,13 +939,8 @@ static void typval_exec_lua(const char *lcmd, size_t lcmd_len, const char *name,
     return;
   }
 
-  for (int i = 0; i < argcount; i++) {
-    if (args[i].v_type == VAR_UNKNOWN) {
-      lua_pushnil(lstate);
-    } else {
-      nlua_push_typval(lstate, &args[i], special);
-    }
-  }
+  PUSH_ALL_TYPVALS(lstate, args, argcount, special);
+
   if (lua_pcall(lstate, argcount, ret_tv ? 1 : 0, 0)) {
     nlua_error(lstate, _("E5108: Error executing lua %.*s"));
     return;
@@ -934,6 +952,14 @@ static void typval_exec_lua(const char *lcmd, size_t lcmd_len, const char *name,
 }
 
 /// Call a LuaCallable given some typvals
+///
+/// Used to call any lua callable passed from Lua into VimL
+///
+/// @param[in]  lstate Lua State
+/// @param[in]  lua_cb Lua Callable
+/// @param[in]  argcount Count of typval arguments
+/// @param[in]  argvars Typval Arguments
+/// @param[out] rettv The return value from the called function.
 int typval_exec_lua_callable(
     lua_State *lstate,
     LuaCallable lua_cb,
@@ -942,22 +968,32 @@ int typval_exec_lua_callable(
     typval_T *rettv
 )
 {
-    LuaRef cb = lua_cb.func_ref;
+  int offset = 0;
+  LuaRef cb = lua_cb.func_ref;
 
-    nlua_pushref(lstate, cb);
+  if (cb == LUA_NOREF) {
+    // This shouldn't happen.
+    luaL_error(lstate, "Invalid function passed to VimL");
+    return ERROR_OTHER;
+  }
 
-    for (int i = 0; i < argcount; i++) {
-        nlua_push_typval(lstate, &argvars[i], false);
-    }
+  nlua_pushref(lstate, cb);
 
-    if (lua_pcall(lstate, argcount, 1, 0)) {
-        luaL_error(lstate, "nlua_CFunction_func_call failed.");
-        return ERROR_OTHER;
-    }
+  if (lua_cb.table_ref != LUA_NOREF) {
+    offset += 1;
+    nlua_pushref(lstate, lua_cb.table_ref);
+  }
+
+  PUSH_ALL_TYPVALS(lstate, argvars, argcount, false);
+
+  if (lua_pcall(lstate, argcount + offset, 1, 0)) {
+    luaL_error(lstate, "nlua_CFunction_func_call failed.");
+    return ERROR_OTHER;
+  }
 
-    nlua_pop_typval(lstate, rettv);
+  nlua_pop_typval(lstate, rettv);
 
-    return ERROR_NONE;
+  return ERROR_NONE;
 }
 
 /// Execute Lua string
@@ -1331,7 +1367,91 @@ void nlua_CFunction_func_free(void *state)
     LuaCFunctionState *funcstate = (LuaCFunctionState *)state;
 
     nlua_unref(lstate, funcstate->lua_callable.func_ref);
+    nlua_unref(lstate, funcstate->lua_callable.table_ref);
     xfree(funcstate);
 }
 
+bool nlua_is_table_from_lua(typval_T *const arg)
+{
+  if (arg->v_type != VAR_DICT && arg->v_type != VAR_LIST) {
+    return false;
+  }
+
+  if (arg->v_type == VAR_DICT) {
+    return arg->vval.v_dict->lua_table_ref > 0
+      && arg->vval.v_dict->lua_table_ref != LUA_NOREF;
+  } else if (arg->v_type == VAR_LIST) {
+    return arg->vval.v_list->lua_table_ref > 0
+      && arg->vval.v_list->lua_table_ref != LUA_NOREF;
+  }
+
+  return false;
+}
 
+char_u *nlua_register_table_as_callable(typval_T *const arg)
+{
+  if (!nlua_is_table_from_lua(arg)) {
+    return NULL;
+  }
+
+  LuaRef table_ref;
+  if (arg->v_type == VAR_DICT) {
+    table_ref = arg->vval.v_dict->lua_table_ref;
+  } else if (arg->v_type == VAR_LIST) {
+    table_ref = arg->vval.v_list->lua_table_ref;
+  } else {
+    return NULL;
+  }
+
+  lua_State *const lstate = nlua_enter();
+
+  int top = lua_gettop(lstate);
+
+  nlua_pushref(lstate, table_ref);
+  if (!lua_getmetatable(lstate, -1)) {
+    return NULL;
+  }
+
+  lua_getfield(lstate, -1, "__call");
+  if (!lua_isfunction(lstate, -1)) {
+    return NULL;
+  }
+
+  LuaRef new_table_ref = nlua_newref(lstate, table_ref);
+
+  LuaCFunctionState *state = xmalloc(sizeof(LuaCFunctionState));
+  state->lua_callable.func_ref = nlua_ref(lstate, -1);
+  state->lua_callable.table_ref = new_table_ref;
+
+  char_u *name = register_cfunc(
+      &nlua_CFunction_func_call,
+      &nlua_CFunction_func_free,
+      state);
+
+
+  lua_pop(lstate, 3);
+  assert(top == lua_gettop(lstate));
+
+  return name;
+}
+
+/// Helper function to free a list_T
+void nlua_free_typval_list(list_T *const l)
+{
+  if (l->lua_table_ref != LUA_NOREF && l->lua_table_ref > 0) {
+    lua_State *const lstate = nlua_enter();
+    nlua_unref(lstate, l->lua_table_ref);
+    l->lua_table_ref = LUA_NOREF;
+  }
+}
+
+
+/// Helper function to free a dict_T
+void nlua_free_typval_dict(dict_T *const d)
+{
+  if (d->lua_table_ref != LUA_NOREF && d->lua_table_ref > 0) {
+    lua_State *const lstate = nlua_enter();
+    nlua_unref(lstate, d->lua_table_ref);
+    d->lua_table_ref = LUA_NOREF;
+  }
+}
diff --git a/test/functional/lua/luaeval_spec.lua b/test/functional/lua/luaeval_spec.lua
index 4faacecd86..964ea4561e 100644
--- a/test/functional/lua/luaeval_spec.lua
+++ b/test/functional/lua/luaeval_spec.lua
@@ -295,13 +295,12 @@ describe('luaeval()', function()
     ]])
   end)
 
-  -- TODO(tjdevries): Need to figure
-  pending('should work with metatables using __call', function()
-    eq(true, exec_lua [[
+  it('should work with metatables using __call', function()
+    eq(1, exec_lua [[
       local this_is_local_variable = false
-      local callable_table = setmetatable({}, {
-        __call = function(...)
-          this_is_local_variable = true
+      local callable_table = setmetatable({x = 1}, {
+        __call = function(t, ...)
+          this_is_local_variable = t.x
         end
       })
 
@@ -315,6 +314,73 @@ describe('luaeval()', function()
     ]])
   end)
 
+  it('should handle being called from a timer once.', function()
+    eq(3, exec_lua [[
+      local this_is_local_variable = false
+      local callable_table = setmetatable({5, 4, 3, 2, 1}, {
+        __call = function(t, ...) this_is_local_variable = t[3] end
+      })
+
+      vim.fn.timer_start(5, callable_table)
+      vim.wait(1000, function()
+        return this_is_local_variable
+      end)
+
+      return this_is_local_variable
+    ]])
+  end)
+
+  it('should call functions once with __call metamethod', function()
+    eq(true, exec_lua [[
+      local this_is_local_variable = false
+      local callable_table = setmetatable({a = true, b = false}, {
+        __call = function(t, ...) this_is_local_variable = t.a end
+      })
+
+      assert(getmetatable(callable_table).__call)
+      vim.fn.call(callable_table, {})
+
+      return this_is_local_variable
+    ]])
+  end)
+
+  it('should work with lists using __call', function()
+    eq(3, exec_lua [[
+      local this_is_local_variable = false
+      local mt = {
+        __call = function(t, ...)
+          this_is_local_variable = t[3]
+        end
+      }
+      local callable_table = setmetatable({5, 4, 3, 2, 1}, mt)
+
+      -- Call it once...
+      vim.fn.timer_start(5, callable_table)
+      vim.wait(1000, function()
+        return this_is_local_variable
+      end)
+
+      assert(this_is_local_variable)
+      this_is_local_variable = false
+
+      vim.fn.timer_start(5, callable_table)
+      vim.wait(1000, function()
+        return this_is_local_variable
+      end)
+
+      return this_is_local_variable
+    ]])
+  end)
+
+  it('should not work with tables not using __call', function()
+    eq({false, 'Vim:E921: Invalid callback argument'}, exec_lua [[
+      local this_is_local_variable = false
+      local callable_table = setmetatable({x = 1}, {})
+
+      return {pcall(function() vim.fn.timer_start(5, callable_table) end)}
+    ]])
+  end)
+
   it('correctly converts containers with type_idx', function()
     eq(5, eval('type(luaeval("{[vim.type_idx]=vim.types.float, [vim.val_idx]=0}"))'))
     eq(4, eval([[type(luaeval('{[vim.type_idx]=vim.types.dictionary}'))]]))