patch 8.2.3276: Vim9: exists() can only be evaluated at runtime

Problem:    Vim9: exists() can only be evaluated at runtime.
Solution:   Evaluate at compile time for option name literals. (closes #8437)

src/evalfunc.c

@@ -49,7 +49,6 @@ static void f_escape(typval_T *argvars, typval_T *rettv);
 static void f_eval(typval_T *argvars, typval_T *rettv);
 static void f_eventhandler(typval_T *argvars, typval_T *rettv);
 static void f_execute(typval_T *argvars, typval_T *rettv);
-static void f_exists(typval_T *argvars, typval_T *rettv);
 static void f_expand(typval_T *argvars, typval_T *rettv);
 static void f_expandcmd(typval_T *argvars, typval_T *rettv);
 static void f_feedkeys(typval_T *argvars, typval_T *rettv);
@@ -3521,7 +3520,7 @@ f_execute(typval_T *argvars, typval_T *rettv)
 /*
  * "exists()" function
  */
-    static void
+    void
 f_exists(typval_T *argvars, typval_T *rettv)
 {
     char_u	*p;

src/proto/evalfunc.pro

@@ -18,6 +18,7 @@ buf_T *get_buf_arg(typval_T *arg);
 win_T *get_optional_window(typval_T *argvars, int idx);
 void execute_redir_str(char_u *value, int value_len);
 void execute_common(typval_T *argvars, typval_T *rettv, int arg_off);
+void f_exists(typval_T *argvars, typval_T *rettv);
 void f_has(typval_T *argvars, typval_T *rettv);
 int dynamic_feature(char_u *feature);
 void mzscheme_call_vim(char_u *name, typval_T *args, typval_T *rettv);

src/testdir/test_vim9_builtin.vim

@@ -790,6 +790,25 @@ enddef
 def Test_exists()
   CheckDefAndScriptFailure2(['exists(10)'], 'E1013: Argument 1: type mismatch, expected string but got number', 'E1174: String required for argument 1')
   call assert_equal(1, exists('&tabstop'))
+
+  if exists('+newoption')
+    if &newoption == 'ok'
+    endif
+  endif
+  if exists('&newoption')
+    if &newoption == 'ok'
+    endif
+  endif
+  if exists('+tabstop')
+    assert_equal(8, &tabstop)
+  else
+    assert_report('tabstop option not existing?')
+  endif
+  if exists('&tabstop')
+    assert_equal(8, &tabstop)
+  else
+    assert_report('tabstop option not existing?')
+  endif
 enddef
 
 def Test_expand()

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3276,
 /**/
     3275,
 /**/

src/vim9compile.c

@@ -3395,8 +3395,10 @@ compile_call(
     int		is_autoload;
     int		is_searchpair;
 
-    // we can evaluate "has('name')" at compile time
+    // We can evaluate "has('name')" at compile time.
-    if (varlen == 3 && STRNCMP(*arg, "has", 3) == 0)
+    // We can evaluate some "exists()" values at compile time.
+    if ((varlen == 3 && STRNCMP(*arg, "has", 3) == 0)
+	    || (varlen == 6 && STRNCMP(*arg, "exists", 6) == 0))
     {
 	char_u	    *s = skipwhite(*arg + varlen + 1);
 	typval_T    argvars[2];
@@ -3408,7 +3410,9 @@ compile_call(
 	    (void)eval_lit_string(&s, &argvars[0], TRUE);
 	s = skipwhite(s);
 	if (*s == ')' && argvars[0].v_type == VAR_STRING
-		&& !dynamic_feature(argvars[0].vval.v_string))
+	       && ((**arg == 'h' && !dynamic_feature(argvars[0].vval.v_string))
+		    || (**arg == 'e' && (*argvars[0].vval.v_string == '+'
+			    || *argvars[0].vval.v_string == '&'))))
 	{
 	    typval_T	*tv = &ppconst->pp_tv[ppconst->pp_used];
 
@@ -3416,7 +3420,10 @@ compile_call(
 	    argvars[1].v_type = VAR_UNKNOWN;
 	    tv->v_type = VAR_NUMBER;
 	    tv->vval.v_number = 0;
+	    if (**arg == 'h')
 		f_has(argvars, tv);
+	    else
+		f_exists(argvars, tv);
 	    clear_tv(&argvars[0]);
 	    ++ppconst->pp_used;
 	    return OK;