lua: Add ability to pass lua functions directly to vimL

src/nvim/lua/converter.c

@@ -19,6 +19,7 @@
 #include "nvim/globals.h"
 #include "nvim/message.h"
 #include "nvim/eval/typval.h"
+#include "nvim/eval/userfunc.h"
 #include "nvim/ascii.h"
 #include "nvim/macros.h"
 
@@ -50,6 +51,7 @@ typedef struct {
 #define LUA_PUSH_STATIC_STRING(lstate, s) \
     lua_pushlstring(lstate, s, sizeof(s) - 1)
 
+
 static LuaTableProps nlua_traverse_table(lua_State *const lstate)
   FUNC_ATTR_NONNULL_ALL FUNC_ATTR_WARN_UNUSED_RESULT
 {
@@ -384,6 +386,20 @@ bool nlua_pop_typval(lua_State *lstate, typval_T *ret_tv)
 nlua_pop_typval_table_processing_end:
         break;
       }
+      case LUA_TFUNCTION: {
+        LuaCFunctionState *state = xmalloc(sizeof(LuaCFunctionState));
+
+        state->lua_callable.func_ref = nlua_ref(lstate, -1);
+
+        char_u *name = register_cfunc(
+            &nlua_CFunction_func_call,
+            &nlua_CFunction_func_free,
+            state);
+
+        cur.tv->v_type = VAR_FUNC;
+        cur.tv->vval.v_string = vim_strsave(name);
+        break;
+      }
       case LUA_TUSERDATA: {
         nlua_pushref(lstate, nlua_nil_ref);
         bool is_nil = lua_rawequal(lstate, -2, -1);

src/nvim/lua/converter.h

@@ -9,6 +9,14 @@
 #include "nvim/func_attr.h"
 #include "nvim/eval.h"
 
+typedef struct {
+    LuaRef func_ref;
+} LuaCallable;
+
+typedef struct {
+    LuaCallable lua_callable;
+} LuaCFunctionState;
+
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "lua/converter.h.generated.h"
 #endif

src/nvim/lua/executor.c

@@ -35,8 +35,8 @@
 #include "nvim/os/os.h"
 #endif
 
-#include "nvim/lua/executor.h"
 #include "nvim/lua/converter.h"
+#include "nvim/lua/executor.h"
 #include "nvim/lua/treesitter.h"
 
 #include "luv/luv.h"
@@ -833,7 +833,7 @@ void executor_free_luaref(LuaRef ref)
   nlua_unref(lstate, ref);
 }
 
-/// push a value referenced in the regirstry
+/// push a value referenced in the registry
 void nlua_pushref(lua_State *lstate, LuaRef ref)
 {
   lua_rawgeti(lstate, LUA_REGISTRYINDEX, ref);
@@ -933,6 +933,33 @@ static void typval_exec_lua(const char *lcmd, size_t lcmd_len, const char *name,
   }
 }
 
+/// Call a LuaCallable given some typvals
+int typval_exec_lua_callable(
+    lua_State *lstate,
+    LuaCallable lua_cb,
+    int argcount,
+    typval_T *argvars,
+    typval_T *rettv
+)
+{
+    LuaRef cb = lua_cb.func_ref;
+
+    nlua_pushref(lstate, cb);
+
+    for (int i = 0; i < argcount; i++) {
+        nlua_push_typval(lstate, &argvars[i], false);
+    }
+
+    if (lua_pcall(lstate, argcount, 1, 0)) {
+        luaL_error(lstate, "nlua_CFunction_func_call failed.");
+        return ERROR_OTHER;
+    }
+
+    nlua_pop_typval(lstate, rettv);
+
+    return ERROR_NONE;
+}
+
 /// Execute Lua string
 ///
 /// Used for nvim_exec_lua().
@@ -1280,3 +1307,31 @@ static int regex_match_line(lua_State *lstate)
 
   return nret;
 }
+
+int nlua_CFunction_func_call(
+    int argcount,
+    typval_T *argvars,
+    typval_T *rettv,
+    void *state)
+{
+    lua_State *const lstate = nlua_enter();
+    LuaCFunctionState *funcstate = (LuaCFunctionState *)state;
+
+    return typval_exec_lua_callable(
+        lstate,
+        funcstate->lua_callable,
+        argcount,
+        argvars,
+        rettv);
+}
+/// Required functions for lua c functions as VimL callbacks
+void nlua_CFunction_func_free(void *state)
+{
+    lua_State *const lstate = nlua_enter();
+    LuaCFunctionState *funcstate = (LuaCFunctionState *)state;
+
+    nlua_unref(lstate, funcstate->lua_callable.func_ref);
+    xfree(funcstate);
+}
+
+

src/nvim/lua/executor.h

@@ -8,6 +8,7 @@
 #include "nvim/func_attr.h"
 #include "nvim/eval/typval.h"
 #include "nvim/ex_cmds_defs.h"
+#include "nvim/lua/converter.h"
 
 // Generated by msgpack-gen.lua
 void nlua_add_api_functions(lua_State *lstate) REAL_FATTR_NONNULL_ALL;

src/nvim/lua/vim.lua

@@ -272,6 +272,10 @@ vim.fn = setmetatable({}, {
   end
 })
 
+vim.funcref = function(viml_func_name)
+  return vim.fn[viml_func_name]
+end
+
 -- These are for loading runtime modules lazily since they aren't available in
 -- the nvim binary as specified in executor.c
 local function __index(t, key)