patch 8.2.2308: Vim9: no error when assigning lambda to funcref

Problem:    Vim9: no error when assigning lambda to funcref without return
            value.
Solution:   Default return value to "any". (closes #7629)

src/testdir/test_vim9_assign.vim

@@ -1091,6 +1091,13 @@ def Test_assign_lambda()
       assert_equal(123, FuncRef_Any())
   END
   CheckScriptSuccess(lines)
+
+  lines =<< trim END
+      var Ref: func(number)
+      Ref = (j) => !j
+  END
+  CheckDefFailure(lines, 'E1012: Type mismatch; expected func(number) but got func(any): bool')
+  CheckScriptFailure(['vim9script'] + lines, 'E1012: Type mismatch; expected func(number) but got func(any): any')
 enddef
 
 def Test_heredoc()

src/testdir/test_vim9_func.vim

@@ -1508,7 +1508,7 @@ def Test_unknown_function()
       'delfunc g:NotExist'], 'E700:')
 enddef
 
-def RefFunc(Ref: func(string): string): string
+def RefFunc(Ref: func(any): any): string
   return Ref('more')
 enddef
 

src/userfunc.c

@@ -668,7 +668,7 @@ get_lambda_tv(
 		    goto errret;
 	    }
 	    else
-		fp->uf_ret_type = &t_unknown;
+		fp->uf_ret_type = &t_any;
 	}
 
 	fp->uf_lines = newlines;

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2308,
 /**/
     2307,
 /**/

src/vim9compile.c

@@ -857,7 +857,9 @@ use_typecheck(type_T *actual, type_T *expected)
 	    || (actual->tt_type == VAR_FUNC
 		&& (expected->tt_type == VAR_FUNC
 					   || expected->tt_type == VAR_PARTIAL)
-		&& (actual->tt_member == &t_any || actual->tt_argcount < 0)))
+		&& (actual->tt_member == &t_any || actual->tt_argcount < 0)
+		&& ((actual->tt_member == &t_void)
+					 == (expected->tt_member == &t_void))))
 	return TRUE;
     if ((actual->tt_type == VAR_LIST || actual->tt_type == VAR_DICT)
 				       && actual->tt_type == expected->tt_type)
@@ -4812,7 +4814,8 @@ compile_return(char_u *arg, int check_return_type, cctx_T *cctx)
 	{
 	    stack_type = ((type_T **)stack->ga_data)[stack->ga_len - 1];
 	    if (check_return_type && (cctx->ctx_ufunc->uf_ret_type == NULL
-				|| cctx->ctx_ufunc->uf_ret_type == &t_unknown))
+				|| cctx->ctx_ufunc->uf_ret_type == &t_unknown
+				|| cctx->ctx_ufunc->uf_ret_type == &t_any))
 	    {
 		cctx->ctx_ufunc->uf_ret_type = stack_type;
 	    }