vim-patch:8.2.3751: cannot assign a lambda to an option that takes a function

Problem:    Cannot assign a lambda to an option that takes a function.
Solution:   Automatically convert the lambda to a string. (Yegappan
            Lakshmanan, closes vim/vim#9286)

https://github.com/vim/vim/commit/6409553b6e3b4de4e1d72b8ee5445595214581ff

Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>

11 files changed, 287 insertions, 48 deletions

diff --git a/src/nvim/api/options.c b/src/nvim/api/options.c
index ec1f19cf6a..92f20fff48 100644
--- a/src/nvim/api/options.c
+++ b/src/nvim/api/options.c
@@ -487,7 +487,7 @@ static getoption_T access_option_value(char *key, long *numval, char **stringval
                                        bool get, Error *err)
 {
   if (get) {
-    return get_option_value(key, numval, stringval, opt_flags);
+    return get_option_value(key, numval, stringval, NULL, opt_flags);
   } else {
     char *errmsg;
     if ((errmsg = set_option_value(key, *numval, *stringval, opt_flags))) {
diff --git a/src/nvim/context.c b/src/nvim/context.c
index 34692cdf64..c765b95733 100644
--- a/src/nvim/context.c
+++ b/src/nvim/context.c
@@ -131,7 +131,7 @@ bool ctx_restore(Context *ctx, const int flags)
   }
 
   char *op_shada;
-  get_option_value("shada", NULL, &op_shada, OPT_GLOBAL);
+  get_option_value("shada", NULL, &op_shada, NULL, OPT_GLOBAL);
   set_option_value("shada", 0L, "!,'100,%", OPT_GLOBAL);
 
   if (flags & kCtxRegs) {
diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 0848326d90..a4fadcd7bc 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -3689,10 +3689,10 @@ static int eval_index(char **arg, typval_T *rettv, int evaluate, int verbose)
 int get_option_tv(const char **const arg, typval_T *const rettv, const bool evaluate)
   FUNC_ATTR_NONNULL_ARG(1)
 {
-  int opt_flags;
+  int scope;
 
   // Isolate the option name and find its value.
-  char *option_end = (char *)find_option_end(arg, &opt_flags);
+  char *option_end = (char *)find_option_end(arg, &scope);
   if (option_end == NULL) {
     if (rettv != NULL) {
       semsg(_("E112: Option name missing: %s"), *arg);
@@ -3712,7 +3712,7 @@ int get_option_tv(const char **const arg, typval_T *const rettv, const bool eval
   char c = *option_end;
   *option_end = NUL;
   getoption_T opt_type = get_option_value(*arg, &numval,
-                                          rettv == NULL ? NULL : &stringval, opt_flags);
+                                          rettv == NULL ? NULL : &stringval, NULL, scope);
 
   if (opt_type == gov_unknown) {
     if (rettv != NULL) {
@@ -7794,19 +7794,19 @@ void ex_execute(exarg_T *eap)
 ///
 /// @return  NULL when no option name found.  Otherwise pointer to the char
 ///          after the option name.
-const char *find_option_end(const char **const arg, int *const opt_flags)
+const char *find_option_end(const char **const arg, int *const scope)
 {
   const char *p = *arg;
 
   p++;
   if (*p == 'g' && p[1] == ':') {
-    *opt_flags = OPT_GLOBAL;
+    *scope = OPT_GLOBAL;
     p += 2;
   } else if (*p == 'l' && p[1] == ':') {
-    *opt_flags = OPT_LOCAL;
+    *scope = OPT_LOCAL;
     p += 2;
   } else {
-    *opt_flags = 0;
+    *scope = 0;
   }
 
   if (!ASCII_ISALPHA(*p)) {
diff --git a/src/nvim/eval/vars.c b/src/nvim/eval/vars.c
index 139e7ed66b..6c4d33df89 100644
--- a/src/nvim/eval/vars.c
+++ b/src/nvim/eval/vars.c
@@ -560,8 +560,6 @@ static char *ex_let_one(char *arg, typval_T *const tv, const bool copy, const bo
 {
   char *arg_end = NULL;
   int len;
-  int opt_flags;
-  char *tofree = NULL;
 
   // ":let $VAR = expr": Set environment variable.
   if (*arg == '$') {
@@ -582,12 +580,12 @@ static char *ex_let_one(char *arg, typval_T *const tv, const bool copy, const bo
                  && vim_strchr(endchars, *skipwhite(arg)) == NULL) {
         emsg(_(e_letunexp));
       } else if (!check_secure()) {
+        char *tofree = NULL;
         const char c1 = name[len];
         name[len] = NUL;
         const char *p = tv_get_string_chk(tv);
         if (p != NULL && op != NULL && *op == '.') {
           char *s = vim_getenv(name);
-
           if (s != NULL) {
             tofree = concat_str(s, p);
             p = (const char *)tofree;
@@ -611,7 +609,8 @@ static char *ex_let_one(char *arg, typval_T *const tv, const bool copy, const bo
       return NULL;
     }
     // Find the end of the name.
-    char *const p = (char *)find_option_end((const char **)&arg, &opt_flags);
+    int scope;
+    char *const p = (char *)find_option_end((const char **)&arg, &scope);
     if (p == NULL
         || (endchars != NULL
             && vim_strchr(endchars, *skipwhite(p)) == NULL)) {
@@ -623,11 +622,13 @@ static char *ex_let_one(char *arg, typval_T *const tv, const bool copy, const bo
       char *stringval = NULL;
       const char *s = NULL;
       bool failed = false;
+      uint32_t opt_p_flags;
+      char *tofree = NULL;
 
       const char c1 = *p;
       *p = NUL;
 
-      opt_type = get_option_value(arg, &numval, &stringval, opt_flags);
+      opt_type = get_option_value(arg, &numval, &stringval, &opt_p_flags, scope);
       if (opt_type == gov_bool
           || opt_type == gov_number
           || opt_type == gov_hidden_bool
@@ -636,8 +637,13 @@ static char *ex_let_one(char *arg, typval_T *const tv, const bool copy, const bo
         n = (long)tv_get_number(tv);
       }
 
-      // Avoid setting a string option to the text "v:false" or similar.
-      if (tv->v_type != VAR_BOOL && tv->v_type != VAR_SPECIAL) {
+      if ((opt_p_flags & P_FUNC) && tv_is_func(*tv)) {
+        // If the option can be set to a function reference or a lambda
+        // and the passed value is a function reference, then convert it to
+        // the name (string) of the function reference.
+        s = tofree = encode_tv2string(tv, NULL);
+      } else if (tv->v_type != VAR_BOOL && tv->v_type != VAR_SPECIAL) {
+        // Avoid setting a string option to the text "v:false" or similar.
         s = tv_get_string_chk(tv);
       }
 
@@ -674,7 +680,7 @@ static char *ex_let_one(char *arg, typval_T *const tv, const bool copy, const bo
 
       if (!failed) {
         if (opt_type != gov_string || s != NULL) {
-          char *err = set_option_value(arg, n, s, opt_flags);
+          char *err = set_option_value(arg, n, s, scope);
           arg_end = p;
           if (err != NULL) {
             emsg(_(err));
@@ -685,6 +691,7 @@ static char *ex_let_one(char *arg, typval_T *const tv, const bool copy, const bo
       }
       *p = c1;
       xfree(stringval);
+      xfree(tofree);
     }
     // ":let @r = expr": Set register contents.
   } else if (*arg == '@') {
diff --git a/src/nvim/generators/gen_options.lua b/src/nvim/generators/gen_options.lua
index 4e4dd83367..af21d44eaf 100644
--- a/src/nvim/generators/gen_options.lua
+++ b/src/nvim/generators/gen_options.lua
@@ -29,14 +29,14 @@ local type_flags={
 }
 
 local redraw_flags={
+  ui_option='P_UI_OPTION',
+  tabline='P_RTABL',
   statuslines='P_RSTAT',
-  tabline = 'P_RTABL',
   current_window='P_RWIN',
   current_window_only='P_RWINONLY',
   current_buffer='P_RBUF',
   all_windows='P_RALL',
   curswant='P_CURSWANT',
-  ui_option='P_UI_OPTION',
 }
 
 local list_flags={
@@ -78,6 +78,7 @@ local get_flags = function(o)
     {'deny_in_modelines', 'P_NO_ML'},
     {'deny_duplicates', 'P_NODUP'},
     {'modelineexpr', 'P_MLE'},
+    {'func'}
   }) do
     local key_name = flag_desc[1]
     local def_name = flag_desc[2] or ('P_' .. key_name:upper())
diff --git a/src/nvim/option.c b/src/nvim/option.c
index da3fad0d61..c0a1f14463 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -2842,6 +2842,7 @@ int findoption(const char *const arg)
 /// Gets the value for an option.
 ///
 /// @param stringval  NULL when only checking existence
+/// @param flagsp     set to the option flags (P_xxxx) (if not NULL)
 ///
 /// @returns:
 ///           Number option: gov_number, *numval gets value.
@@ -2851,7 +2852,8 @@ int findoption(const char *const arg)
 ///           Hidden Toggle option: gov_hidden_bool.
 ///           Hidden String option: gov_hidden_string.
 ///           Unknown option: gov_unknown.
-getoption_T get_option_value(const char *name, long *numval, char **stringval, int opt_flags)
+getoption_T get_option_value(const char *name, long *numval, char **stringval, uint32_t *flagsp,
+                             int scope)
 {
   if (get_tty_option(name, stringval)) {
     return gov_string;
@@ -2862,7 +2864,12 @@ getoption_T get_option_value(const char *name, long *numval, char **stringval, i
     return gov_unknown;
   }
 
-  char_u *varp = (char_u *)get_varp_scope(&(options[opt_idx]), opt_flags);
+  char_u *varp = (char_u *)get_varp_scope(&(options[opt_idx]), scope);
+
+  if (flagsp != NULL) {
+    // Return the P_xxxx option flags.
+    *flagsp = options[opt_idx].flags;
+  }
 
   if (options[opt_idx].flags & P_STRING) {
     if (varp == NULL) {  // hidden option
@@ -3092,7 +3099,7 @@ char *set_option_value(const char *const name, const long number, const char *co
           numval = -1;
         } else {
           char *s = NULL;
-          (void)get_option_value(name, &numval, &s, OPT_GLOBAL);
+          (void)get_option_value(name, &numval, &s, NULL, OPT_GLOBAL);
         }
       }
       if (flags & P_NUM) {
@@ -3701,15 +3708,17 @@ void unset_global_local_option(char *name, void *from)
 }
 
 /// Get pointer to option variable, depending on local or global scope.
-char *get_varp_scope(vimoption_T *p, int opt_flags)
+///
+/// @param scope  can be OPT_LOCAL, OPT_GLOBAL or a combination.
+char *get_varp_scope(vimoption_T *p, int scope)
 {
-  if ((opt_flags & OPT_GLOBAL) && p->indir != PV_NONE) {
+  if ((scope & OPT_GLOBAL) && p->indir != PV_NONE) {
     if (p->var == VAR_WIN) {
       return GLOBAL_WO(get_varp(p));
     }
     return (char *)p->var;
   }
-  if ((opt_flags & OPT_LOCAL) && ((int)p->indir & PV_BOTH)) {
+  if ((scope & OPT_LOCAL) && ((int)p->indir & PV_BOTH)) {
     switch ((int)p->indir) {
     case PV_FP:
       return (char *)&(curbuf->b_p_fp);
@@ -4863,9 +4872,9 @@ void ExpandOldSetting(int *num_file, char ***file)
 /// NameBuff[].  Must not be called with a hidden option!
 ///
 /// @param opt_flags  OPT_GLOBAL and/or OPT_LOCAL
-static void option_value2string(vimoption_T *opp, int opt_flags)
+static void option_value2string(vimoption_T *opp, int scope)
 {
-  char_u *varp = (char_u *)get_varp_scope(opp, opt_flags);
+  char_u *varp = (char_u *)get_varp_scope(opp, scope);
 
   if (opp->flags & P_NUM) {
     long wc = 0;
diff --git a/src/nvim/option_defs.h b/src/nvim/option_defs.h
index 7c33773e41..d505e75be4 100644
--- a/src/nvim/option_defs.h
+++ b/src/nvim/option_defs.h
@@ -24,6 +24,7 @@
 #define P_NO_MKRC      0x200U       ///< don't include in :mkvimrc output
 
 // when option changed, what to display:
+#define P_UI_OPTION    0x400U       ///< send option to remote UI
 #define P_RTABL        0x800U       ///< redraw tabline
 #define P_RSTAT        0x1000U      ///< redraw status lines
 #define P_RWIN         0x2000U      ///< redraw current window and recompute text
@@ -50,9 +51,9 @@
 #define P_NDNAME       0x8000000U   ///< only normal dir name chars allowed
 #define P_RWINONLY     0x10000000U  ///< only redraw current window
 #define P_MLE          0x20000000U  ///< under control of 'modelineexpr'
+#define P_FUNC         0x40000000U  ///< accept a function reference or a lambda
 
-#define P_NO_DEF_EXP   0x40000000U  ///< Do not expand default value.
-#define P_UI_OPTION    0x80000000U  ///< send option to remote ui
+#define P_NO_DEF_EXP   0x80000000U  ///< Do not expand default value.
 
 /// Flags for option-setting functions
 ///
diff --git a/src/nvim/options.lua b/src/nvim/options.lua
index 3a59becb33..e938760e67 100644
--- a/src/nvim/options.lua
+++ b/src/nvim/options.lua
@@ -10,6 +10,7 @@
 --    secure=nil, gettext=nil, noglob=nil, normal_fname_chars=nil,
 --    pri_mkrc=nil, deny_in_modelines=nil, normal_dname_chars=nil,
 --    modelineexpr=nil,
+--    func=nil,
 --    expand=nil, nodefault=nil, no_mkrc=nil,
 --    alloced=nil,
 --    save_pv_indir=nil,
@@ -455,6 +456,7 @@ return {
       type='string', scope={'buffer'},
       secure=true,
       alloced=true,
+      func=true,
       varname='p_cfu',
       defaults={if_true=""}
     },
@@ -1638,6 +1640,7 @@ return {
       type='string', scope={'buffer'},
       secure=true,
       alloced=true,
+      func=true,
       varname='p_ofu',
       defaults={if_true=""}
     },
@@ -1653,6 +1656,7 @@ return {
       short_desc=N_("function to be called for |g@| operator"),
       type='string', scope={'global'},
       secure=true,
+      func=true,
       varname='p_opfunc',
       defaults={if_true=""}
     },
@@ -1835,6 +1839,8 @@ return {
       full_name='quickfixtextfunc', abbreviation='qftf',
       short_desc=N_("customize the quickfix window"),
       type='string', scope={'global'},
+      secure=true,
+      func=true,
       varname='p_qftf',
       defaults={if_true=""}
     },
@@ -2408,6 +2414,8 @@ return {
       full_name='tagfunc', abbreviation='tfu',
       short_desc=N_("function used to perform tag searches"),
       type='string', scope={'buffer'},
+      secure=true,
+      func=true,
       varname='p_tfu',
       defaults={if_true=""}
     },
@@ -2538,6 +2546,7 @@ return {
       type='string', scope={'global', 'buffer'},
       secure=true,
       alloced=true,
+      func=true,
       varname='p_tsrfu',
       defaults={if_true=""}
     },
diff --git a/src/nvim/spell.c b/src/nvim/spell.c
index e76ac49b5d..1b78aa4d72 100644
--- a/src/nvim/spell.c
+++ b/src/nvim/spell.c
@@ -3145,7 +3145,7 @@ void ex_spelldump(exarg_T *eap)
   }
   char *spl;
   long dummy;
-  (void)get_option_value("spl", &dummy, &spl, OPT_LOCAL);
+  (void)get_option_value("spl", &dummy, &spl, NULL, OPT_LOCAL);
 
   // Create a new empty buffer in a new window.
   do_cmdline_cmd("new");
diff --git a/src/nvim/testdir/test_ins_complete.vim b/src/nvim/testdir/test_ins_complete.vim
index 0478ad1516..8b5f9a189f 100644
--- a/src/nvim/testdir/test_ins_complete.vim
+++ b/src/nvim/testdir/test_ins_complete.vim
@@ -1302,13 +1302,22 @@ func Test_completefunc_callback()
 
   " Using a funcref variable to set 'completefunc'
   let Fn = function('MycompleteFunc1')
+  let &completefunc = Fn
+  new | only
+  call setline(1, 'two')
+  let g:MycompleteFunc1_args = []
+  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+  call assert_equal([[1, ''], [0, 'two']], g:MycompleteFunc1_args)
+  bw!
+
+  " Using string(funcref_variable) to set 'completefunc'
+  let Fn = function('MycompleteFunc1')
   let &completefunc = string(Fn)
   new | only
   call setline(1, 'two')
   let g:MycompleteFunc1_args = []
   call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
   call assert_equal([[1, ''], [0, 'two']], g:MycompleteFunc1_args)
-  call assert_fails('let &completefunc = Fn', 'E729:')
   bw!
 
   " Test for using a funcref()
@@ -1326,13 +1335,22 @@ func Test_completefunc_callback()
 
   " Using a funcref variable to set 'completefunc'
   let Fn = funcref('MycompleteFunc2')
+  let &completefunc = Fn
+  new | only
+  call setline(1, 'four')
+  let g:MycompleteFunc2_args = []
+  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+  call assert_equal([[1, ''], [0, 'four']], g:MycompleteFunc2_args)
+  bw!
+
+  " Using a string(funcref_variable) to set 'completefunc'
+  let Fn = funcref('MycompleteFunc2')
   let &completefunc = string(Fn)
   new | only
   call setline(1, 'four')
   let g:MycompleteFunc2_args = []
   call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
   call assert_equal([[1, ''], [0, 'four']], g:MycompleteFunc2_args)
-  call assert_fails('let &completefunc = Fn', 'E729:')
   bw!
 
   " Test for using a lambda function
@@ -1349,6 +1367,15 @@ func Test_completefunc_callback()
   bw!
 
   " Set 'completefunc' to a lambda expression
+  let &completefunc = {a, b -> MycompleteFunc3(a, b)}
+  new | only
+  call setline(1, 'six')
+  let g:MycompleteFunc3_args = []
+  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+  call assert_equal([[1, ''], [0, 'six']], g:MycompleteFunc3_args)
+  bw!
+
+  " Set 'completefunc' to string(lambda_expression)
   let &completefunc = '{a, b -> MycompleteFunc3(a, b)}'
   new | only
   call setline(1, 'six')
@@ -1359,18 +1386,27 @@ func Test_completefunc_callback()
 
   " Set 'completefunc' to a variable with a lambda expression
   let Lambda = {a, b -> MycompleteFunc3(a, b)}
+  let &completefunc = Lambda
+  new | only
+  call setline(1, 'seven')
+  let g:MycompleteFunc3_args = []
+  call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+  call assert_equal([[1, ''], [0, 'seven']], g:MycompleteFunc3_args)
+  bw!
+
+  " Set 'completefunc' to a string(variable with a lambda expression)
+  let Lambda = {a, b -> MycompleteFunc3(a, b)}
   let &completefunc = string(Lambda)
   new | only
   call setline(1, 'seven')
   let g:MycompleteFunc3_args = []
   call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
   call assert_equal([[1, ''], [0, 'seven']], g:MycompleteFunc3_args)
-  call assert_fails('let &completefunc = Lambda', 'E729:')
   bw!
 
   " Test for using a lambda function with incorrect return value
   let Lambda = {s -> strlen(s)}
-  let &completefunc = string(Lambda)
+  let &completefunc = Lambda
   new | only
   call setline(1, 'eight')
   call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
@@ -1382,7 +1418,7 @@ func Test_completefunc_callback()
 
   call assert_fails("set completefunc=function('abc')", "E700:")
   call assert_fails("set completefunc=funcref('abc')", "E700:")
-  let &completefunc = "{a -> 'abc'}"
+  let &completefunc = {a -> 'abc'}
   call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
 
   " Vim9 tests
@@ -1407,6 +1443,15 @@ func Test_completefunc_callback()
       add(g:LambdaComplete1_args, [findstart, base])
       return findstart ? 0 : []
     enddef
+    &completefunc = (a, b) => LambdaComplete1(a, b)
+    new | only
+    setline(1, 'two')
+    g:LambdaComplete1_args = []
+    feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+    assert_equal([[1, ''], [0, 'two']], g:LambdaComplete1_args)
+    bw!
+
+    # Test for using a string(lambda)
     &completefunc = '(a, b) => LambdaComplete1(a, b)'
     new | only
     setline(1, 'two')
@@ -1420,6 +1465,15 @@ func Test_completefunc_callback()
             add(g:LambdaComplete2_args, [findstart, base])
             return findstart ? 0 : []
         }
+    &completefunc = Fn
+    new | only
+    setline(1, 'three')
+    g:LambdaComplete2_args = []
+    feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+    assert_equal([[1, ''], [0, 'three']], g:LambdaComplete2_args)
+    bw!
+
+    # Test for using a string(variable with a lambda expression)
     &completefunc = string(Fn)
     new | only
     setline(1, 'three')
@@ -1462,13 +1516,22 @@ func Test_omnifunc_callback()
 
   " Using a funcref variable to set 'omnifunc'
   let Fn = function('MyomniFunc1')
+  let &omnifunc = Fn
+  new | only
+  call setline(1, 'two')
+  let g:MyomniFunc1_args = []
+  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+  call assert_equal([[1, ''], [0, 'two']], g:MyomniFunc1_args)
+  bw!
+
+  " Using a string(funcref_variable) to set 'omnifunc'
+  let Fn = function('MyomniFunc1')
   let &omnifunc = string(Fn)
   new | only
   call setline(1, 'two')
   let g:MyomniFunc1_args = []
   call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
   call assert_equal([[1, ''], [0, 'two']], g:MyomniFunc1_args)
-  call assert_fails('let &omnifunc = Fn', 'E729:')
   bw!
 
   " Test for using a funcref()
@@ -1486,13 +1549,22 @@ func Test_omnifunc_callback()
 
   " Using a funcref variable to set 'omnifunc'
   let Fn = funcref('MyomniFunc2')
+  let &omnifunc = Fn
+  new | only
+  call setline(1, 'four')
+  let g:MyomniFunc2_args = []
+  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+  call assert_equal([[1, ''], [0, 'four']], g:MyomniFunc2_args)
+  bw!
+
+  " Using a string(funcref_variable) to set 'omnifunc'
+  let Fn = funcref('MyomniFunc2')
   let &omnifunc = string(Fn)
   new | only
   call setline(1, 'four')
   let g:MyomniFunc2_args = []
   call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
   call assert_equal([[1, ''], [0, 'four']], g:MyomniFunc2_args)
-  call assert_fails('let &omnifunc = Fn', 'E729:')
   bw!
 
   " Test for using a lambda function
@@ -1509,6 +1581,15 @@ func Test_omnifunc_callback()
   bw!
 
   " Set 'omnifunc' to a lambda expression
+  let &omnifunc = {a, b -> MyomniFunc3(a, b)}
+  new | only
+  call setline(1, 'six')
+  let g:MyomniFunc3_args = []
+  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+  call assert_equal([[1, ''], [0, 'six']], g:MyomniFunc3_args)
+  bw!
+
+  " Set 'omnifunc' to a string(lambda_expression)
   let &omnifunc = '{a, b -> MyomniFunc3(a, b)}'
   new | only
   call setline(1, 'six')
@@ -1519,18 +1600,27 @@ func Test_omnifunc_callback()
 
   " Set 'omnifunc' to a variable with a lambda expression
   let Lambda = {a, b -> MyomniFunc3(a, b)}
+  let &omnifunc = Lambda
+  new | only
+  call setline(1, 'seven')
+  let g:MyomniFunc3_args = []
+  call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+  call assert_equal([[1, ''], [0, 'seven']], g:MyomniFunc3_args)
+  bw!
+
+  " Set 'omnifunc' to a string(variable with a lambda expression)
+  let Lambda = {a, b -> MyomniFunc3(a, b)}
   let &omnifunc = string(Lambda)
   new | only
   call setline(1, 'seven')
   let g:MyomniFunc3_args = []
   call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
   call assert_equal([[1, ''], [0, 'seven']], g:MyomniFunc3_args)
-  call assert_fails('let &omnifunc = Lambda', 'E729:')
   bw!
 
   " Test for using a lambda function with incorrect return value
   let Lambda = {s -> strlen(s)}
-  let &omnifunc = string(Lambda)
+  let &omnifunc = Lambda
   new | only
   call setline(1, 'eight')
   call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
@@ -1542,7 +1632,7 @@ func Test_omnifunc_callback()
 
   call assert_fails("set omnifunc=function('abc')", "E700:")
   call assert_fails("set omnifunc=funcref('abc')", "E700:")
-  let &omnifunc = "{a -> 'abc'}"
+  let &omnifunc = {a -> 'abc'}
   call feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
 
   " Vim9 tests
@@ -1567,6 +1657,15 @@ func Test_omnifunc_callback()
       add(g:MyomniFunc2_args, [findstart, base])
       return findstart ? 0 : []
     enddef
+    &omnifunc = (a, b) => MyomniFunc2(a, b)
+    new | only
+    setline(1, 'two')
+    g:MyomniFunc2_args = []
+    feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+    assert_equal([[1, ''], [0, 'two']], g:MyomniFunc2_args)
+    bw!
+
+    # Test for using a string(lambda)
     &omnifunc = '(a, b) => MyomniFunc2(a, b)'
     new | only
     setline(1, 'two')
@@ -1577,6 +1676,15 @@ func Test_omnifunc_callback()
 
     # Test for using a variable with a lambda expression
     var Fn: func = (a, b) => MyomniFunc2(a, b)
+    &omnifunc = Fn
+    new | only
+    setline(1, 'three')
+    g:MyomniFunc2_args = []
+    feedkeys("A\<C-X>\<C-O>\<Esc>", 'x')
+    assert_equal([[1, ''], [0, 'three']], g:MyomniFunc2_args)
+    bw!
+
+    # Test for using a string(variable with a lambda expression)
     &omnifunc = string(Fn)
     new | only
     setline(1, 'three')
@@ -1619,13 +1727,22 @@ func Test_thesaurusfunc_callback()
 
   " Using a funcref variable to set 'thesaurusfunc'
   let Fn = function('MytsrFunc1')
+  let &thesaurusfunc = Fn
+  new | only
+  call setline(1, 'two')
+  let g:MytsrFunc1_args = []
+  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+  call assert_equal([[1, ''], [0, 'two']], g:MytsrFunc1_args)
+  bw!
+
+  " Using a string(funcref_variable) to set 'thesaurusfunc'
+  let Fn = function('MytsrFunc1')
   let &thesaurusfunc = string(Fn)
   new | only
   call setline(1, 'two')
   let g:MytsrFunc1_args = []
   call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
   call assert_equal([[1, ''], [0, 'two']], g:MytsrFunc1_args)
-  call assert_fails('let &thesaurusfunc = Fn', 'E729:')
   bw!
 
   " Test for using a funcref()
@@ -1643,13 +1760,22 @@ func Test_thesaurusfunc_callback()
 
   " Using a funcref variable to set 'thesaurusfunc'
   let Fn = funcref('MytsrFunc2')
+  let &thesaurusfunc = Fn
+  new | only
+  call setline(1, 'four')
+  let g:MytsrFunc2_args = []
+  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+  call assert_equal([[1, ''], [0, 'four']], g:MytsrFunc2_args)
+  bw!
+
+  " Using a string(funcref_variable) to set 'thesaurusfunc'
+  let Fn = funcref('MytsrFunc2')
   let &thesaurusfunc = string(Fn)
   new | only
   call setline(1, 'four')
   let g:MytsrFunc2_args = []
   call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
   call assert_equal([[1, ''], [0, 'four']], g:MytsrFunc2_args)
-  call assert_fails('let &thesaurusfunc = Fn', 'E729:')
   bw!
 
   " Test for using a lambda function
@@ -1666,6 +1792,15 @@ func Test_thesaurusfunc_callback()
   bw!
 
   " Set 'thesaurusfunc' to a lambda expression
+  let &thesaurusfunc = {a, b -> MytsrFunc3(a, b)}
+  new | only
+  call setline(1, 'six')
+  let g:MytsrFunc3_args = []
+  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+  call assert_equal([[1, ''], [0, 'six']], g:MytsrFunc3_args)
+  bw!
+
+  " Set 'thesaurusfunc' to a string(lambda expression)
   let &thesaurusfunc = '{a, b -> MytsrFunc3(a, b)}'
   new | only
   call setline(1, 'six')
@@ -1676,18 +1811,27 @@ func Test_thesaurusfunc_callback()
 
   " Set 'thesaurusfunc' to a variable with a lambda expression
   let Lambda = {a, b -> MytsrFunc3(a, b)}
+  let &thesaurusfunc = Lambda
+  new | only
+  call setline(1, 'seven')
+  let g:MytsrFunc3_args = []
+  call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+  call assert_equal([[1, ''], [0, 'seven']], g:MytsrFunc3_args)
+  bw!
+
+  " Set 'thesaurusfunc' to a string(variable with a lambda expression)
+  let Lambda = {a, b -> MytsrFunc3(a, b)}
   let &thesaurusfunc = string(Lambda)
   new | only
   call setline(1, 'seven')
   let g:MytsrFunc3_args = []
   call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
   call assert_equal([[1, ''], [0, 'seven']], g:MytsrFunc3_args)
-  call assert_fails('let &thesaurusfunc = Lambda', 'E729:')
   bw!
 
   " Test for using a lambda function with incorrect return value
   let Lambda = {s -> strlen(s)}
-  let &thesaurusfunc = string(Lambda)
+  let &thesaurusfunc = Lambda
   new | only
   call setline(1, 'eight')
   call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
@@ -1699,7 +1843,7 @@ func Test_thesaurusfunc_callback()
 
   call assert_fails("set thesaurusfunc=function('abc')", "E700:")
   call assert_fails("set thesaurusfunc=funcref('abc')", "E700:")
-  let &thesaurusfunc = "{a -> 'abc'}"
+  let &thesaurusfunc = {a -> 'abc'}
   call feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
 
   " Vim9 tests
@@ -1724,6 +1868,15 @@ func Test_thesaurusfunc_callback()
       add(g:MytsrFunc2_args, [findstart, base])
       return findstart ? 0 : []
     enddef
+    &thesaurusfunc = (a, b) => MytsrFunc2(a, b)
+    new | only
+    setline(1, 'two')
+    g:MytsrFunc2_args = []
+    feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+    assert_equal([[1, ''], [0, 'two']], g:MytsrFunc2_args)
+    bw!
+
+    # Test for using a string(lambda)
     &thesaurusfunc = '(a, b) => MytsrFunc2(a, b)'
     new | only
     setline(1, 'two')
@@ -1734,6 +1887,15 @@ func Test_thesaurusfunc_callback()
 
     # Test for using a variable with a lambda expression
     var Fn: func = (a, b) => MytsrFunc2(a, b)
+    &thesaurusfunc = Fn
+    new | only
+    setline(1, 'three')
+    g:MytsrFunc2_args = []
+    feedkeys("A\<C-X>\<C-T>\<Esc>", 'x')
+    assert_equal([[1, ''], [0, 'three']], g:MytsrFunc2_args)
+    bw!
+
+    # Test for using a string(variable with a lambda expression)
     &thesaurusfunc = string(Fn)
     new | only
     setline(1, 'three')
diff --git a/src/nvim/testdir/test_tagfunc.vim b/src/nvim/testdir/test_tagfunc.vim
index 8690e30e77..06d074c261 100644
--- a/src/nvim/testdir/test_tagfunc.vim
+++ b/src/nvim/testdir/test_tagfunc.vim
@@ -138,12 +138,19 @@ func Test_tagfunc_callback()
 
   " Using a funcref variable to set 'tagfunc'
   let Fn = function('MytagFunc1')
+  let &tagfunc = Fn
+  new | only
+  let g:MytagFunc1_args = []
+  call assert_fails('tag a12', 'E433:')
+  call assert_equal(['a12', '', {}], g:MytagFunc1_args)
+
+  " Using a string(funcref_variable) to set 'tagfunc'
+  let Fn = function('MytagFunc1')
   let &tagfunc = string(Fn)
   new | only
   let g:MytagFunc1_args = []
   call assert_fails('tag a12', 'E433:')
   call assert_equal(['a12', '', {}], g:MytagFunc1_args)
-  call assert_fails('let &tagfunc = Fn', 'E729:')
 
   " Test for using a funcref()
   func MytagFunc2(pat, flags, info)
@@ -158,12 +165,19 @@ func Test_tagfunc_callback()
 
   " Using a funcref variable to set 'tagfunc'
   let Fn = funcref('MytagFunc2')
+  let &tagfunc = Fn
+  new | only
+  let g:MytagFunc2_args = []
+  call assert_fails('tag a14', 'E433:')
+  call assert_equal(['a14', '', {}], g:MytagFunc2_args)
+
+  " Using a string(funcref_variable) to set 'tagfunc'
+  let Fn = funcref('MytagFunc2')
   let &tagfunc = string(Fn)
   new | only
   let g:MytagFunc2_args = []
   call assert_fails('tag a14', 'E433:')
   call assert_equal(['a14', '', {}], g:MytagFunc2_args)
-  call assert_fails('let &tagfunc = Fn', 'E729:')
 
   " Test for using a script local function
   set tagfunc=<SID>ScriptLocalTagFunc
@@ -174,6 +188,14 @@ func Test_tagfunc_callback()
 
   " Test for using a script local funcref variable
   let Fn = function("s:ScriptLocalTagFunc")
+  let &tagfunc= Fn
+  new | only
+  let g:ScriptLocalFuncArgs = []
+  call assert_fails('tag a16', 'E433:')
+  call assert_equal(['a16', '', {}], g:ScriptLocalFuncArgs)
+
+  " Test for using a string(script local funcref variable)
+  let Fn = function("s:ScriptLocalTagFunc")
   let &tagfunc= string(Fn)
   new | only
   let g:ScriptLocalFuncArgs = []
@@ -192,6 +214,13 @@ func Test_tagfunc_callback()
   call assert_equal(['a17', '', {}], g:MytagFunc3_args)
 
   " Set 'tagfunc' to a lambda expression
+  let &tagfunc = {a, b, c -> MytagFunc3(a, b, c)}
+  new | only
+  let g:MytagFunc3_args = []
+  call assert_fails('tag a18', 'E433:')
+  call assert_equal(['a18', '', {}], g:MytagFunc3_args)
+
+  " Set 'tagfunc' to a string(lambda expression)
   let &tagfunc = '{a, b, c -> MytagFunc3(a, b, c)}'
   new | only
   let g:MytagFunc3_args = []
@@ -200,12 +229,19 @@ func Test_tagfunc_callback()
 
   " Set 'tagfunc' to a variable with a lambda expression
   let Lambda = {a, b, c -> MytagFunc3(a, b, c)}
+  let &tagfunc = Lambda
+  new | only
+  let g:MytagFunc3_args = []
+  call assert_fails("tag a19", "E433:")
+  call assert_equal(['a19', '', {}], g:MytagFunc3_args)
+
+  " Set 'tagfunc' to a string(variable with a lambda expression)
+  let Lambda = {a, b, c -> MytagFunc3(a, b, c)}
   let &tagfunc = string(Lambda)
   new | only
   let g:MytagFunc3_args = []
   call assert_fails("tag a19", "E433:")
   call assert_equal(['a19', '', {}], g:MytagFunc3_args)
-  call assert_fails('let &tagfunc = Lambda', 'E729:')
 
   " Test for using a lambda function with incorrect return value
   let Lambda = {s -> strlen(s)}
@@ -242,6 +278,13 @@ func Test_tagfunc_callback()
       g:MytagFunc2_args = [pat, flags, info]
       return null
     enddef
+    &tagfunc = (a, b, c) => MytagFunc2(a, b, c)
+    new | only
+    g:MytagFunc2_args = []
+    assert_fails('tag a20', 'E433:')
+    assert_equal(['a20', '', {}], g:MytagFunc2_args)
+
+    # Test for using a string(lambda)
     &tagfunc = '(a, b, c) => MytagFunc2(a, b, c)'
     new | only
     g:MytagFunc2_args = []
@@ -250,6 +293,13 @@ func Test_tagfunc_callback()
 
     # Test for using a variable with a lambda expression
     var Fn: func = (a, b, c) => MytagFunc2(a, b, c)
+    &tagfunc = Fn
+    new | only
+    g:MytagFunc2_args = []
+    assert_fails('tag a30', 'E433:')
+    assert_equal(['a30', '', {}], g:MytagFunc2_args)
+
+    # Test for using a variable with a lambda expression
     &tagfunc = string(Fn)
     new | only
     g:MytagFunc2_args = []