vim-patch:9.0.0419: the :defer command does not check the function arguments

Problem:    The :defer command does not check the function argument count and
            types.
Solution:   Check the function arguments when adding a deferred function.

169003289f

Cherry-pick check_internal_func() from Vim, but use EvalFuncDef pointer
as first argument.

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/eval/funcs.c

@@ -228,6 +228,31 @@ const EvalFuncDef *find_internal_func(const char *const name)
   return index >= 0 ? &functions[index] : NULL;
 }
 
+/// Check the argument count to use for internal function "fdef".
+/// @return  -1 for failure, 0 if no method base accepted, 1 if method base is
+/// first argument, 2 if method base is second argument, etc.
+int check_internal_func(const EvalFuncDef *const fdef, const int argcount)
+  FUNC_ATTR_NONNULL_ALL
+{
+  int res;
+
+  if (argcount < fdef->min_argc) {
+    res = FCERR_TOOFEW;
+  } else if (argcount > fdef->max_argc) {
+    res = FCERR_TOOMANY;
+  } else {
+    return fdef->base_arg;
+  }
+
+  const char *const name = fdef->name;
+  if (res == FCERR_TOOMANY) {
+    semsg(_(e_toomanyarg), name);
+  } else {
+    semsg(_(e_toofewarg), name);
+  }
+  return -1;
+}
+
 int call_internal_func(const char *const fname, const int argcount, typval_T *const argvars,
                        typval_T *const rettv)
   FUNC_ATTR_NONNULL_ALL

src/nvim/eval/userfunc.c

@@ -72,7 +72,7 @@ static funccall_T *current_funccal = NULL;
 // item in it is still being used.
 static funccall_T *previous_funccal = NULL;
 
-static const char *e_unknownfunc = N_("E117: Unknown function: %s");
+static const char *e_unknown_function_str = N_("E117: Unknown function: %s");
 static const char *e_funcexts = N_("E122: Function %s already exists, add ! to replace it");
 static const char *e_funcdict = N_("E717: Dictionary entry already exists");
 static const char *e_funcref = N_("E718: Funcref required");
@@ -1523,14 +1523,14 @@ varnumber_T callback_call_retnr(Callback *callback, int argcount, typval_T *argv
 /// Give an error message for the result of a function.
 /// Nothing if "error" is FCERR_NONE.
 static void user_func_error(int error, const char *name, funcexe_T *funcexe)
-  FUNC_ATTR_NONNULL_ALL
+  FUNC_ATTR_NONNULL_ARG(2)
 {
   switch (error) {
   case FCERR_UNKNOWN:
     if (funcexe->fe_found_var) {
       semsg(_(e_not_callable_type_str), name);
     } else {
-      emsg_funcname(e_unknownfunc, name);
+      emsg_funcname(e_unknown_function_str, name);
     }
     break;
   case FCERR_NOTMETHOD:
@@ -1543,7 +1543,7 @@ static void user_func_error(int error, const char *name, funcexe_T *funcexe)
     emsg_funcname(_(e_toomanyarg), name);
     break;
   case FCERR_TOOFEW:
-    emsg_funcname(N_("E119: Not enough arguments for function: %s"), name);
+    emsg_funcname(_(e_toofewarg), name);
     break;
   case FCERR_SCRIPT:
     emsg_funcname(N_("E120: Using <SID> not in a script context: %s"), name);
@@ -3172,6 +3172,29 @@ static int ex_defer_inner(char *name, char **arg, const partial_T *const partial
   }
   int r = get_func_arguments(arg, evalarg, false, argvars + partial_argc, &argcount);
   argcount += partial_argc;
+
+  if (r == OK) {
+    if (builtin_function(name, -1)) {
+      const EvalFuncDef *const fdef = find_internal_func(name);
+      if (fdef == NULL) {
+        emsg_funcname(e_unknown_function_str, name);
+        r = FAIL;
+      } else if (check_internal_func(fdef, argcount) == -1) {
+        r = FAIL;
+      }
+    } else {
+      ufunc_T *ufunc = find_func(name);
+      // we tolerate an unknown function here, it might be defined later
+      if (ufunc != NULL) {
+        int error = check_user_func_argcount(ufunc, argcount);
+        if (error != FCERR_UNKNOWN) {
+          user_func_error(error, name, NULL);
+          r = FAIL;
+        }
+      }
+    }
+  }
+
   if (r == FAIL) {
     while (--argcount >= 0) {
       tv_clear(&argvars[argcount]);

src/nvim/globals.h

@@ -953,6 +953,7 @@ EXTERN const char e_dictreq[] INIT(= N_("E715: Dictionary required"));
 EXTERN const char e_blobidx[] INIT(= N_("E979: Blob index out of range: %" PRId64));
 EXTERN const char e_invalblob[] INIT(= N_("E978: Invalid operation for Blob"));
 EXTERN const char e_toomanyarg[] INIT(= N_("E118: Too many arguments for function: %s"));
+EXTERN const char e_toofewarg[] INIT(= N_("E119: Not enough arguments for function: %s"));
 EXTERN const char e_dictkey[] INIT(= N_("E716: Key not present in Dictionary: \"%s\""));
 EXTERN const char e_listreq[] INIT(= N_("E714: List required"));
 EXTERN const char e_listblobreq[] INIT(= N_("E897: List or Blob required"));