vim-patch:8.2.1471: :const only locks the variable, not the value (#12765)

Problem:    :const only locks the variable, not the value.
Solution:   Lock the value as ":lockvar 1 var" would do. (closes vim/vim#6719)
https://github.com/vim/vim/commit/241572794f7e93d2f8b762de2300e5f7e4f07628

2 files changed, 9 insertions, 5 deletions

diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index b37fd85659..8e3109b8be 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -9045,7 +9045,7 @@ static void set_var_const(const char *name, const size_t name_len,
   }
 
   if (is_const) {
-    v->di_tv.v_lock |= VAR_LOCKED;
+    tv_item_lock(&v->di_tv, 1, true);
   }
 }
 
diff --git a/src/nvim/testdir/test_const.vim b/src/nvim/testdir/test_const.vim
index eaf200e9bb..fc7ea71f6e 100644
--- a/src/nvim/testdir/test_const.vim
+++ b/src/nvim/testdir/test_const.vim
@@ -36,6 +36,7 @@ func Test_define_var_with_lock()
     call assert_fails('let s = "vim"', 'E741:')
     call assert_fails('let F = funcref("s:noop")', 'E741:')
     call assert_fails('let l = [1, 2, 3]', 'E741:')
+    call assert_fails('call filter(l, "v:val % 2 == 0")', 'E741:')
     call assert_fails('let d = {"foo": 10}', 'E741:')
     if has('channel')
         call assert_fails('let j = test_null_job()', 'E741:')
@@ -247,11 +248,14 @@ func Test_lock_depth_is_1()
     const l = [1, 2, 3]
     const d = {'foo': 10}
 
-    " Modify list
-    call add(l, 4)
+    " Modify list - setting item is OK, adding/removing items not
     let l[0] = 42
+    call assert_fails('call add(l, 4)', 'E741:')
+    call assert_fails('unlet l[1]', 'E741:')
 
-    " Modify dict
-    let d['bar'] = 'hello'
+    " Modify dict - changing item is OK, adding/removing items not
+    let d['foo'] = 'hello'
     let d.foo = 44
+    call assert_fails("let d['bar'] = 'hello'", 'E741:')
+    call assert_fails("unlet d['foo']", 'E741:')
 endfunc