refactor(typval): change FC_CFUNC abstraction into FC_LUAREF

"cfuncs" was only ever used to wrap luarefs. As vim8script is
finished and will not be developed further, support for "cfuncs"
for other usecases are not planned. This abstraction was immediately
broken anyway in order to get luarefs out of userfuncs again.

Even if a new kind of userfunc needs to be invented in the future,
likely just extending the FC_... flag union directy, instead of
invoking unnecessary heap object and c function pointer indirection,
will be a more straightforward design pattern.

7 files changed, 36 insertions, 85 deletions

diff --git a/src/nvim/api/private/converter.c b/src/nvim/api/private/converter.c
index 8724ef4432..b6b3c83f3c 100644
--- a/src/nvim/api/private/converter.c
+++ b/src/nvim/api/private/converter.c
@@ -65,8 +65,8 @@ typedef struct {
 #define TYPVAL_ENCODE_CONV_FUNC_START(tv, fun) \
   do { \
     ufunc_T *fp = find_func(fun); \
-    if (fp != NULL && fp->uf_cb == nlua_CFunction_func_call) { \
-      LuaRef ref = api_new_luaref(((LuaCFunctionState *)fp->uf_cb_state)->lua_callable.func_ref); \
+    if (fp != NULL && (fp->uf_flags & FC_LUAREF)) { \
+      LuaRef ref = api_new_luaref(fp->uf_luaref); \
       kvi_push(edata->stack, LUAREF_OBJ(ref)); \
     } else { \
       TYPVAL_ENCODE_CONV_NIL(tv); \
@@ -351,10 +351,7 @@ bool object_to_vim(Object obj, typval_T *tv, Error *err)
   }
 
   case kObjectTypeLuaRef: {
-    LuaCFunctionState *state = xmalloc(sizeof(LuaCFunctionState));
-    state->lua_callable.func_ref = api_new_luaref(obj.data.luaref);
-    char *name =
-      (char *)register_cfunc(&nlua_CFunction_func_call, &nlua_CFunction_func_free, state);
+    char *name = (char *)register_luafunc(api_new_luaref(obj.data.luaref));
     tv->v_type = VAR_FUNC;
     tv->vval.v_string = xstrdup(name);
     break;
diff --git a/src/nvim/eval/typval.h b/src/nvim/eval/typval.h
index cf7b04c8ce..6373ead1a3 100644
--- a/src/nvim/eval/typval.h
+++ b/src/nvim/eval/typval.h
@@ -286,12 +286,6 @@ typedef struct {
 /// Number of fixed variables used for arguments
 #define FIXVAR_CNT 12
 
-/// 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 and any associated state.
-typedef void (*cfunc_free_T)(void *state);
-
 // Structure to hold info for a function that is currently being executed.
 typedef struct funccall_S funccall_T;
 
@@ -330,10 +324,7 @@ struct ufunc {
   garray_T uf_lines;         ///< function lines
   int uf_profiling;     ///< true when func is being profiled
   int uf_prof_initialized;
-  // Managing cfuncs
-  cfunc_T uf_cb;            ///< C function extension callback
-  cfunc_free_T uf_cb_free;       ///< C function extension free callback
-  void *uf_cb_state;      ///< State of C function extension.
+  LuaRef uf_luaref;      ///< lua callback, used if (uf_flags & FC_LUAREF)
   // Profiling the function as a whole.
   int uf_tm_count;      ///< nr of calls
   proftime_T uf_tm_total;      ///< time spent in function + children
diff --git a/src/nvim/eval/userfunc.c b/src/nvim/eval/userfunc.c
index 36bc51179c..a899e1579b 100644
--- a/src/nvim/eval/userfunc.c
+++ b/src/nvim/eval/userfunc.c
@@ -28,20 +28,6 @@
 #include "nvim/ui.h"
 #include "nvim/vim.h"
 
-// flags used in uf_flags
-#define FC_ABORT    0x01          // abort function on error
-#define FC_RANGE    0x02          // function accepts range
-#define FC_DICT     0x04          // Dict function, uses "self"
-#define FC_CLOSURE  0x08          // closure, uses outer scope variables
-#define FC_DELETED  0x10          // :delfunction used while uf_refcount > 0
-#define FC_REMOVED  0x20          // function redefined while uf_refcount > 0
-#define FC_SANDBOX  0x40          // function defined in the sandbox
-#define FC_DEAD     0x80          // function kept only for reference to dfunc
-#define FC_EXPORT   0x100         // "export def Func()"
-#define FC_NOARGS   0x200         // no a: variables in lambda
-#define FC_VIM9     0x400         // defined in vim9 script file
-#define FC_CFUNC    0x800         // C function extension
-
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "eval/userfunc.c.generated.h"
 #endif
@@ -758,9 +744,9 @@ static void func_clear_items(ufunc_T *fp)
   ga_clear_strings(&(fp->uf_lines));
   XFREE_CLEAR(fp->uf_name_exp);
 
-  if (fp->uf_cb_free != NULL) {
-    fp->uf_cb_free(fp->uf_cb_state);
-    fp->uf_cb_free = NULL;
+  if (fp->uf_flags & FC_LUAREF) {
+    api_free_luaref(fp->uf_luaref);
+    fp->uf_luaref = LUA_NOREF;
   }
 
   XFREE_CLEAR(fp->uf_tml_count);
@@ -1538,9 +1524,8 @@ int call_func(const char *funcname, int len, typval_T *rettv, int argcount_in, t
 
       if (fp != NULL && (fp->uf_flags & FC_DELETED)) {
         error = ERROR_DELETED;
-      } else if (fp != NULL && (fp->uf_flags & FC_CFUNC)) {
-        cfunc_T cb = fp->uf_cb;
-        error = (*cb)(argcount, argvars, rettv, fp->uf_cb_state);
+      } else if (fp != NULL && (fp->uf_flags & FC_LUAREF)) {
+        error = typval_exec_lua_callable(fp->uf_luaref, argcount, argvars, rettv);
       } else if (fp != NULL) {
         if (funcexe->argv_func != NULL) {
           // postponed filling in the arguments, do it now
@@ -3552,20 +3537,18 @@ bool set_ref_in_func(char_u *name, ufunc_T *fp_in, int copyID)
   return abort;
 }
 
-/// Registers a C extension user function.
-char_u *register_cfunc(cfunc_T cb, cfunc_free_T cb_free, void *state)
+/// Registers a luaref as a lambda.
+char_u *register_luafunc(LuaRef ref)
 {
   char_u *name = get_lambda_name();
   ufunc_T *fp = xcalloc(1, offsetof(ufunc_T, uf_name) + STRLEN(name) + 1);
 
   fp->uf_refcount = 1;
   fp->uf_varargs = true;
-  fp->uf_flags = FC_CFUNC;
+  fp->uf_flags = FC_LUAREF;
   fp->uf_calls = 0;
   fp->uf_script_ctx = current_sctx;
-  fp->uf_cb = cb;
-  fp->uf_cb_free = cb_free;
-  fp->uf_cb_state = state;
+  fp->uf_luaref = ref;
 
   STRCPY(fp->uf_name, name);
   hash_add(&func_hashtab, UF2HIKEY(fp));
diff --git a/src/nvim/eval/userfunc.h b/src/nvim/eval/userfunc.h
index 4b7007aae9..9811f2afb3 100644
--- a/src/nvim/eval/userfunc.h
+++ b/src/nvim/eval/userfunc.h
@@ -9,6 +9,20 @@
 #define HIKEY2UF(p)  ((ufunc_T *)(p - offsetof(ufunc_T, uf_name)))
 #define HI2UF(hi)    HIKEY2UF((hi)->hi_key)
 
+// flags used in uf_flags
+#define FC_ABORT    0x01          // abort function on error
+#define FC_RANGE    0x02          // function accepts range
+#define FC_DICT     0x04          // Dict function, uses "self"
+#define FC_CLOSURE  0x08          // closure, uses outer scope variables
+#define FC_DELETED  0x10          // :delfunction used while uf_refcount > 0
+#define FC_REMOVED  0x20          // function redefined while uf_refcount > 0
+#define FC_SANDBOX  0x40          // function defined in the sandbox
+#define FC_DEAD     0x80          // function kept only for reference to dfunc
+#define FC_EXPORT   0x100         // "export def Func()"
+#define FC_NOARGS   0x200         // no a: variables in lambda
+#define FC_VIM9     0x400         // defined in vim9 script file
+#define FC_LUAREF  0x800          // luaref callback
+
 ///< Structure used by trans_function_name()
 typedef struct {
   dict_T *fd_dict;  ///< Dictionary used.
diff --git a/src/nvim/lua/converter.c b/src/nvim/lua/converter.c
index 21dd5139d7..735a75a6f1 100644
--- a/src/nvim/lua/converter.c
+++ b/src/nvim/lua/converter.c
@@ -385,12 +385,9 @@ nlua_pop_typval_table_processing_end:
       break;
     }
     case LUA_TFUNCTION: {
-      LuaCFunctionState *state = xmalloc(sizeof(LuaCFunctionState));
-      state->lua_callable.func_ref = nlua_ref_global(lstate, -1);
+      LuaRef func = nlua_ref_global(lstate, -1);
 
-      char *name = (char *)register_cfunc(&nlua_CFunction_func_call,
-                                          &nlua_CFunction_func_free,
-                                          state);
+      char *name = (char *)register_luafunc(func);
 
       cur.tv->v_type = VAR_FUNC;
       cur.tv->vval.v_string = xstrdup(name);
@@ -476,8 +473,8 @@ static bool typval_conv_special = false;
 #define TYPVAL_ENCODE_CONV_FUNC_START(tv, fun) \
   do { \
     ufunc_T *fp = find_func(fun); \
-    if (fp != NULL && fp->uf_cb == nlua_CFunction_func_call) { \
-      nlua_pushref(lstate, ((LuaCFunctionState *)fp->uf_cb_state)->lua_callable.func_ref); \
+    if (fp != NULL && fp->uf_flags & FC_LUAREF) { \
+      nlua_pushref(lstate, fp->uf_luaref); \
     } else { \
       TYPVAL_ENCODE_CONV_NIL(tv); \
     } \
diff --git a/src/nvim/lua/converter.h b/src/nvim/lua/converter.h
index f6a85900ba..ddc0acfbfa 100644
--- a/src/nvim/lua/converter.h
+++ b/src/nvim/lua/converter.h
@@ -9,14 +9,6 @@
 #include "nvim/eval/typval.h"
 #include "nvim/func_attr.h"
 
-typedef struct {
-  LuaRef func_ref;
-} LuaCallable;
-
-typedef struct {
-  LuaCallable lua_callable;
-} LuaCFunctionState;
-
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "lua/converter.h.generated.h"
 #endif
diff --git a/src/nvim/lua/executor.c b/src/nvim/lua/executor.c
index 1013cf76f9..857e2111d6 100644
--- a/src/nvim/lua/executor.c
+++ b/src/nvim/lua/executor.c
@@ -1425,12 +1425,11 @@ int nlua_source_using_linegetter(LineGetter fgetline, void *cookie, char *name)
 /// @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, int argcount, typval_T *argvars,
-                             typval_T *rettv)
+int typval_exec_lua_callable(LuaRef lua_cb, int argcount, typval_T *argvars, typval_T *rettv)
 {
-  LuaRef cb = lua_cb.func_ref;
+  lua_State *lstate = global_lstate;
 
-  nlua_pushref(lstate, cb);
+  nlua_pushref(lstate, lua_cb);
 
   PUSH_ALL_TYPVALS(lstate, argvars, argcount, false);
 
@@ -1833,26 +1832,6 @@ static int nlua_is_thread(lua_State *lstate)
   return 1;
 }
 
-// Required functions for lua c functions as VimL callbacks
-
-int nlua_CFunction_func_call(int argcount, typval_T *argvars, typval_T *rettv, void *state)
-{
-  lua_State *const lstate = global_lstate;
-  LuaCFunctionState *funcstate = (LuaCFunctionState *)state;
-
-  return typval_exec_lua_callable(lstate, funcstate->lua_callable,
-                                  argcount, argvars, rettv);
-}
-
-void nlua_CFunction_func_free(void *state)
-{
-  lua_State *const lstate = global_lstate;
-  LuaCFunctionState *funcstate = (LuaCFunctionState *)state;
-
-  nlua_unref_global(lstate, funcstate->lua_callable.func_ref);
-  xfree(funcstate);
-}
-
 bool nlua_is_table_from_lua(typval_T *const arg)
 {
   if (arg->v_type == VAR_DICT) {
@@ -1898,11 +1877,9 @@ char_u *nlua_register_table_as_callable(typval_T *const arg)
   }
   lua_pop(lstate, 2);  // [table]
 
-  LuaCFunctionState *state = xmalloc(sizeof(LuaCFunctionState));
-  state->lua_callable.func_ref = nlua_ref_global(lstate, -1);
+  LuaRef func = nlua_ref_global(lstate, -1);
 
-  char_u *name = register_cfunc(&nlua_CFunction_func_call,
-                                &nlua_CFunction_func_free, state);
+  char_u *name = register_luafunc(func);
 
   lua_pop(lstate, 1);  // []
   assert(top == lua_gettop(lstate));