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.

3 files changed, 24 insertions, 36 deletions

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.