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.

https://github.com/vim/vim/commit/169003289fb4b2ad18fd7f5807e0d05efff0be85

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

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

1 files changed, 25 insertions, 0 deletions

diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index f53b283c79..b064379210 100644
--- a/src/nvim/eval/funcs.c
+++ b/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