vim-patch:8.2.3783: confusing error for using a variable as a function

Problem:    Confusing error for using a variable as a function.
Solution:   If a function is not found but there is a variable, give a more
            useful error. (issue vim/vim#9310)

https://github.com/vim/vim/commit/2ef9156b4284e4a52613c36e3d4667245273a28d

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

7 files changed, 46 insertions, 19 deletions

diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index ccb615602f..f80ca5346c 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -1236,7 +1236,7 @@ Note that the dot is also used for String concatenation.  To avoid confusion
 always put spaces around the dot for String concatenation.
 
 
-expr8(expr1, ...)	|Funcref| function call
+expr8(expr1, ...)	|Funcref| function call		*E1085*
 
 When expr8 is a |Funcref| type variable, invoke the function it refers to.
 
diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 1d9061186a..b8daa78c79 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -2220,6 +2220,7 @@ static int eval_func(char **const arg, evalarg_T *const evalarg, char *const nam
   const bool evaluate = flags & EVAL_EVALUATE;
   char *s = name;
   int len = name_len;
+  bool found_var = false;
 
   if (!evaluate) {
     check_vars(s, (size_t)len);
@@ -2228,7 +2229,7 @@ static int eval_func(char **const arg, evalarg_T *const evalarg, char *const nam
   // If "s" is the name of a variable of type VAR_FUNC
   // use its contents.
   partial_T *partial;
-  s = deref_func_name(s, &len, &partial, !evaluate);
+  s = deref_func_name(s, &len, &partial, !evaluate, &found_var);
 
   // Need to make a copy, in case evaluating the arguments makes
   // the name invalid.
@@ -2241,6 +2242,7 @@ static int eval_func(char **const arg, evalarg_T *const evalarg, char *const nam
   funcexe.fe_evaluate = evaluate;
   funcexe.fe_partial = partial;
   funcexe.fe_basetv = basetv;
+  funcexe.fe_found_var = found_var;
   int ret = get_func_tv(s, len, rettv, arg, evalarg, &funcexe);
 
   xfree(s);
diff --git a/src/nvim/eval/userfunc.c b/src/nvim/eval/userfunc.c
index 9705bc93db..a348588106 100644
--- a/src/nvim/eval/userfunc.c
+++ b/src/nvim/eval/userfunc.c
@@ -65,6 +65,7 @@ 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_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");
@@ -401,9 +402,11 @@ errret:
 ///                        is not needed.
 /// @param[in]  no_autoload  If true, do not source autoload scripts if function
 ///                          was not found.
+/// @param[out]  found_var  If not NULL and a variable was found set it to true.
 ///
 /// @return name of the function.
-char *deref_func_name(const char *name, int *lenp, partial_T **const partialp, bool no_autoload)
+char *deref_func_name(const char *name, int *lenp, partial_T **const partialp, bool no_autoload,
+                      bool *found_var)
   FUNC_ATTR_NONNULL_ARG(1, 2)
 {
   if (partialp != NULL) {
@@ -411,18 +414,25 @@ char *deref_func_name(const char *name, int *lenp, partial_T **const partialp, b
   }
 
   dictitem_T *const v = find_var(name, (size_t)(*lenp), NULL, no_autoload);
-  if (v != NULL && v->di_tv.v_type == VAR_FUNC) {
-    if (v->di_tv.vval.v_string == NULL) {  // just in case
+  if (v == NULL) {
+    return (char *)name;
+  }
+  typval_T *const tv = &v->di_tv;
+  if (found_var != NULL) {
+    *found_var = true;
+  }
+
+  if (tv->v_type == VAR_FUNC) {
+    if (tv->vval.v_string == NULL) {  // just in case
       *lenp = 0;
       return "";
     }
-    *lenp = (int)strlen(v->di_tv.vval.v_string);
-    return v->di_tv.vval.v_string;
+    *lenp = (int)strlen(tv->vval.v_string);
+    return tv->vval.v_string;
   }
 
-  if (v != NULL && v->di_tv.v_type == VAR_PARTIAL) {
-    partial_T *const pt = v->di_tv.vval.v_partial;
-
+  if (tv->v_type == VAR_PARTIAL) {
+    partial_T *const pt = tv->vval.v_partial;
     if (pt == NULL) {  // just in case
       *lenp = 0;
       return "";
@@ -1454,12 +1464,16 @@ 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)
+static void user_func_error(int error, const char *name, funcexe_T *funcexe)
   FUNC_ATTR_NONNULL_ALL
 {
   switch (error) {
   case FCERR_UNKNOWN:
-    emsg_funcname(N_("E117: Unknown function: %s"), name);
+    if (funcexe->fe_found_var) {
+      semsg(_(e_not_callable_type_str), name);
+    } else {
+      emsg_funcname(e_unknownfunc, name);
+    }
     break;
   case FCERR_NOTMETHOD:
     emsg_funcname(N_("E276: Cannot use function as a method: %s"), name);
@@ -1654,7 +1668,7 @@ theend:
   // Report an error unless the argument evaluation or function call has been
   // cancelled due to an aborting error, an interrupt, or an exception.
   if (!aborting()) {
-    user_func_error(error, (name != NULL) ? name : funcname);
+    user_func_error(error, (name != NULL) ? name : funcname, funcexe);
   }
 
   // clear the copies made from the partial
@@ -1846,14 +1860,13 @@ char *trans_function_name(char **pp, bool skip, int flags, funcdict_T *fdp, part
   // Check if the name is a Funcref.  If so, use the value.
   if (lv.ll_exp_name != NULL) {
     len = (int)strlen(lv.ll_exp_name);
-    name = deref_func_name(lv.ll_exp_name, &len, partial,
-                           flags & TFN_NO_AUTOLOAD);
+    name = deref_func_name(lv.ll_exp_name, &len, partial, flags & TFN_NO_AUTOLOAD, NULL);
     if (name == lv.ll_exp_name) {
       name = NULL;
     }
   } else if (!(flags & TFN_NO_DEREF)) {
     len = (int)(end - *pp);
-    name = deref_func_name(*pp, &len, partial, flags & TFN_NO_AUTOLOAD);
+    name = deref_func_name(*pp, &len, partial, flags & TFN_NO_AUTOLOAD, NULL);
     if (name == *pp) {
       name = NULL;
     }
@@ -3070,7 +3083,8 @@ void ex_call(exarg_T *eap)
   // contents. For VAR_PARTIAL get its partial, unless we already have one
   // from trans_function_name().
   len = (int)strlen(tofree);
-  name = deref_func_name(tofree, &len, partial != NULL ? NULL : &partial, false);
+  bool found_var = false;
+  name = deref_func_name(tofree, &len, partial != NULL ? NULL : &partial, false, &found_var);
 
   // Skip white space to allow ":call func ()".  Not good, but required for
   // backward compatibility.
@@ -3104,6 +3118,7 @@ void ex_call(exarg_T *eap)
     funcexe.fe_evaluate = true;
     funcexe.fe_partial = partial;
     funcexe.fe_selfdict = fudi.fd_dict;
+    funcexe.fe_found_var = found_var;
     if (get_func_tv(name, -1, &rettv, &arg, &evalarg, &funcexe) == FAIL) {
       failed = true;
       break;
diff --git a/src/nvim/eval/userfunc.h b/src/nvim/eval/userfunc.h
index d0ad53c43d..4a98afb00e 100644
--- a/src/nvim/eval/userfunc.h
+++ b/src/nvim/eval/userfunc.h
@@ -75,6 +75,8 @@ typedef struct {
   partial_T *fe_partial;  ///< for extra arguments
   dict_T *fe_selfdict;    ///< Dictionary for "self"
   typval_T *fe_basetv;    ///< base for base->method()
+  bool fe_found_var;      ///< if the function is not found then give an
+                          ///< error that a variable is not callable.
 } funcexe_T;
 
 #define FUNCEXE_INIT (funcexe_T) { \
@@ -86,6 +88,7 @@ typedef struct {
   .fe_partial = NULL, \
   .fe_selfdict = NULL, \
   .fe_basetv = NULL, \
+  .fe_found_var = false, \
 }
 
 #define FUNCARG(fp, j)  ((char **)(fp->uf_args.ga_data))[j]
diff --git a/src/nvim/globals.h b/src/nvim/globals.h
index 11888a5df8..3c31d07e33 100644
--- a/src/nvim/globals.h
+++ b/src/nvim/globals.h
@@ -1000,6 +1000,7 @@ EXTERN const char e_fnametoolong[] INIT(= N_("E856: Filename too long"));
 EXTERN const char e_float_as_string[] INIT(= N_("E806: using Float as a String"));
 EXTERN const char e_inval_string[] INIT(= N_("E908: using an invalid value as a String"));
 EXTERN const char e_cannot_edit_other_buf[] INIT(= N_("E788: Not allowed to edit another buffer now"));
+EXTERN const char e_not_callable_type_str[] INIT(= N_("E1085: Not a callable type: %s"));
 
 EXTERN const char e_cmdmap_err[] INIT(= N_("E5520: <Cmd> mapping must end with <CR>"));
 EXTERN const char e_cmdmap_repeated[]
diff --git a/test/functional/lua/luaeval_spec.lua b/test/functional/lua/luaeval_spec.lua
index 9f313eab9e..32bb894be1 100644
--- a/test/functional/lua/luaeval_spec.lua
+++ b/test/functional/lua/luaeval_spec.lua
@@ -545,7 +545,7 @@ describe('v:lua', function()
 
     eq("Vim:E15: Invalid expression: v:['lua'].foo()", pcall_err(eval, "v:['lua'].foo()"))
     eq("Vim(call):E461: Illegal variable name: v:['lua']", pcall_err(command, "call v:['lua'].baar()"))
-    eq("Vim:E117: Unknown function: v:lua", pcall_err(eval, "v:lua()"))
+    eq("Vim:E1085: Not a callable type: v:lua", pcall_err(eval, "v:lua()"))
 
     eq("Vim(let):E46: Cannot change read-only variable \"v:['lua']\"", pcall_err(command, "let v:['lua'] = 'xx'"))
     eq("Vim(let):E46: Cannot change read-only variable \"v:lua\"", pcall_err(command, "let v:lua = 'xx'"))
@@ -553,7 +553,7 @@ describe('v:lua', function()
     eq("Vim:E107: Missing parentheses: v:lua.func", pcall_err(eval, "'bad'->v:lua.func"))
     eq("Vim:E274: No white space allowed before parenthesis", pcall_err(eval, "'bad'->v:lua.func ()"))
     eq("Vim:E107: Missing parentheses: v:lua", pcall_err(eval, "'bad'->v:lua"))
-    eq("Vim:E117: Unknown function: v:lua", pcall_err(eval, "'bad'->v:lua()"))
+    eq("Vim:E1085: Not a callable type: v:lua", pcall_err(eval, "'bad'->v:lua()"))
     eq("Vim:E15: Invalid expression: v:lua.()", pcall_err(eval, "'bad'->v:lua.()"))
   end)
 end)
diff --git a/test/old/testdir/test_functions.vim b/test/old/testdir/test_functions.vim
index abea3b2538..fb53248d5a 100644
--- a/test/old/testdir/test_functions.vim
+++ b/test/old/testdir/test_functions.vim
@@ -2019,6 +2019,12 @@ func Test_call()
   " call assert_fails('call test_null_function()()', 'E1192:')
   " Nvim doesn't have null partials
   " call assert_fails('call test_null_partial()()', 'E117:')
+
+  let lines =<< trim END
+      let Time = 'localtime'
+      call Time()
+  END
+  CheckScriptFailure(lines, 'E1085:')
 endfunc
 
 func Test_char2nr()