patch 8.2.0625: Vim9: confusing error when calling unknown function

Problem:    Vim9: confusing error when calling unknown function.
Solution:   Give error while compiling.

src/testdir/test_vim9_func.vim

@@ -193,10 +193,23 @@ def Test_using_var_as_arg()
 enddef
 
 def Test_call_func_defined_later()
-  call assert_equal('one', DefinedLater('one'))
+  call assert_equal('one', g:DefinedLater('one'))
   call assert_fails('call NotDefined("one")', 'E117:')
 enddef
 
+func DefinedLater(arg)
+  return a:arg
+endfunc
+
+def Test_call_funcref()
+  assert_equal(3, g:SomeFunc('abc'))
+  assert_fails('NotAFunc()', 'E117:')
+  assert_fails('g:NotAFunc()', 'E117:')
+enddef
+
+let SomeFunc = function('len')
+let NotAFunc = 'text'
+
 def CombineFuncrefTypes()
   " same arguments, different return type
   let Ref1: func(bool): string
@@ -217,12 +230,8 @@ def CombineFuncrefTypes()
   Refb3 = g:cond ? Refb1 : Refb2
 enddef
 
-func DefinedLater(arg)
-  return a:arg
-endfunc
-
 def FuncWithForwardCall()
-  return DefinedEvenLater("yes")
+  return g:DefinedEvenLater("yes")
 enddef
 
 def DefinedEvenLater(arg: string): string
@@ -372,9 +381,9 @@ def Test_redef_failure()
   so Xdef
   call delete('Xdef')
 
-  call assert_equal(0, Func0())
-  call assert_equal('Func1', Func1())
-  call assert_equal('Func2', Func2())
+  call assert_equal(0, g:Func0())
+  call assert_equal('Func1', g:Func1())
+  call assert_equal('Func2', g:Func2())
 
   delfunc! Func0
   delfunc! Func1

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    625,
 /**/
     624,
 /**/

src/vim9compile.c

@@ -2463,8 +2463,12 @@ compile_call(char_u **arg, size_t varlen, cctx_T *cctx, int argcount_init)
 	goto theend;
     }
 
-    // The function may be defined only later.  Need to figure out at runtime.
+    // A global function may be defined only later.  Need to figure out at
+    // runtime.
+    if (STRNCMP(namebuf, "g:", 2) == 0)
 	res = generate_UCALL(cctx, name, argcount);
+    else
+	semsg(_(e_unknownfunc), namebuf);
 
 theend:
     vim_free(tofree);

src/vim9execute.c

@@ -460,14 +460,21 @@ call_eval_func(char_u *name, int argcount, ectx_T *ectx, isn_T *iptr)
     if (call_by_name(name, argcount, ectx, iptr) == FAIL
 					  && called_emsg == called_emsg_before)
     {
-	// "name" may be a variable that is a funcref or partial
-	//    if find variable
-	//      call_partial()
-	//    else
-	//      semsg(_(e_unknownfunc), name);
-	emsg("call_eval_func(partial) not implemented yet");
+	dictitem_T	*v;
+
+	v = find_var(name, NULL, FALSE);
+	if (v == NULL)
+	{
+	    semsg(_(e_unknownfunc), name);
 	    return FAIL;
 	}
+	if (v->di_tv.v_type != VAR_PARTIAL && v->di_tv.v_type != VAR_FUNC)
+	{
+	    semsg(_(e_unknownfunc), name);
+	    return FAIL;
+	}
+	return call_partial(&v->di_tv, argcount, ectx);
+    }
     return OK;
 }