patch 8.2.0657: Vim9: no check if called variable is a FuncRef

Problem:    Vim9: no check if called variable is a FuncRef.
Solution:   Add a type check.

src/testdir/test_vim9_expr.vim

@@ -213,6 +213,12 @@ def Test_expr4_equal()
   assert_equal(true, function('g:Test_expr4_equal', [123]) == function('g:Test_expr4_equal', [123]))
   assert_equal(false, function('g:Test_expr4_equal', [123]) == function('g:Test_expr4_is', [123]))
   assert_equal(false, function('g:Test_expr4_equal', [123]) == function('g:Test_expr4_equal', [999]))
+
+  let OneFunc: func
+  let TwoFunc: func
+  OneFunc = function('len')
+  TwoFunc = function('len')
+  assert_equal(true, OneFunc('abc') == TwoFunc('123'))
 enddef
 
 " test != comperator

src/testdir/test_vim9_script.vim

@@ -345,6 +345,9 @@ func Test_wrong_type()
   call CheckDefFailure(['let var: pam'], 'E1010:')
   call CheckDefFailure(['let var: sam'], 'E1010:')
   call CheckDefFailure(['let var: vim'], 'E1010:')
+
+  call CheckDefFailure(['let Ref: number', 'Ref()'], 'E1085:')
+  call CheckDefFailure(['let Ref: string', 'let res = Ref()'], 'E1085:')
 endfunc
 
 func Test_const()

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    657,
 /**/
     656,
 /**/

src/vim9compile.c

@@ -1327,15 +1327,32 @@ generate_UCALL(cctx_T *cctx, char_u *name, int argcount)
 
 /*
  * Generate an ISN_PCALL instruction.
+ * "type" is the type of the FuncRef.
  */
     static int
-generate_PCALL(cctx_T *cctx, int argcount, int at_top)
+generate_PCALL(
+	cctx_T	*cctx,
+	int	argcount,
+	char_u	*name,
+	type_T	*type,
+	int	at_top)
 {
     isn_T	*isn;
     garray_T	*stack = &cctx->ctx_type_stack;
+    type_T	*ret_type;
 
     RETURN_OK_IF_SKIP(cctx);
 
+    if (type->tt_type == VAR_ANY)
+	ret_type = &t_any;
+    else if (type->tt_type == VAR_FUNC || type->tt_type == VAR_PARTIAL)
+	ret_type = type->tt_member;
+    else
+    {
+	semsg(_("E1085: Not a callable type: %s"), name);
+	return FAIL;
+    }
+
     if ((isn = generate_instr(cctx, ISN_PCALL)) == NULL)
 	return FAIL;
     isn->isn_arg.pfunc.cpf_top = at_top;
@@ -1344,7 +1361,7 @@ generate_PCALL(cctx_T *cctx, int argcount, int at_top)
     stack->ga_len -= argcount; // drop the arguments
 
     // drop the funcref/partial, get back the return value
-    ((type_T **)stack->ga_data)[stack->ga_len - 1] = &t_any;
+    ((type_T **)stack->ga_data)[stack->ga_len - 1] = ret_type;
 
     // If partial is above the arguments it must be cleared and replaced with
     // the return value.
@@ -2465,12 +2482,16 @@ compile_call(char_u **arg, size_t varlen, cctx_T *cctx, int argcount_init)
     if (STRNCMP(namebuf, "g:", 2) != 0
 	    && compile_load(&p, namebuf + varlen, cctx, FALSE) == OK)
     {
-	res = generate_PCALL(cctx, argcount, FALSE);
+	garray_T    *stack = &cctx->ctx_type_stack;
+	type_T	    *type;
+
+	type = ((type_T **)stack->ga_data)[stack->ga_len - 1];
+	res = generate_PCALL(cctx, argcount, namebuf, type, FALSE);
 	goto theend;
     }
 
     // A global function may be defined only later.  Need to figure out at
-    // runtime.
+    // runtime.  Also handles a FuncRef at runtime.
     if (STRNCMP(namebuf, "g:", 2) == 0)
 	res = generate_UCALL(cctx, name, argcount);
     else
@@ -3120,13 +3141,17 @@ compile_subscript(
     {
 	if (**arg == '(')
 	{
+	    garray_T    *stack = &cctx->ctx_type_stack;
+	    type_T	*type;
 	    int		argcount = 0;
 
 	    // funcref(arg)
+	    type = ((type_T **)stack->ga_data)[stack->ga_len - 1];
+
 	    *arg = skipwhite(*arg + 1);
 	    if (compile_arguments(arg, cctx, &argcount) == FAIL)
 		return FAIL;
-	    if (generate_PCALL(cctx, argcount, TRUE) == FAIL)
+	    if (generate_PCALL(cctx, argcount, end_leader, type, TRUE) == FAIL)
 		return FAIL;
 	}
 	else if (**arg == '-' && (*arg)[1] == '>')