vim-patch:8.2.0019: cannot number of lines of another buffer

Problem:    Cannot number of lines of another buffer.
Solution:   Add "linecount" to getbufinfo(). (Yasuhiro Matsumoto,
            closes vim/vim#5370)
a9e9679de3

runtime/doc/eval.txt

@@ -4138,6 +4138,8 @@ getbufinfo([{dict}])
 			hidden		TRUE if the buffer is hidden.
 			listed		TRUE if the buffer is listed.
 			lnum		current line number in buffer.
+			linecount	number of lines in the buffer (only
+					valid when loaded)
 			loaded		TRUE if the buffer is loaded.
 			name		full path to the file in the buffer.
 			signs		list of signs placed in the buffer.

src/nvim/eval.c

@@ -9922,6 +9922,7 @@ static dict_T *get_buffer_info(buf_T *buf)
                   buf->b_ffname != NULL ? (const char *)buf->b_ffname : "");
   tv_dict_add_nr(dict, S_LEN("lnum"),
                  buf == curbuf ? curwin->w_cursor.lnum : buflist_findlnum(buf));
+  tv_dict_add_nr(dict, S_LEN("linecount"), buf->b_ml.ml_line_count);
   tv_dict_add_nr(dict, S_LEN("loaded"), buf->b_ml.ml_mfp != NULL);
   tv_dict_add_nr(dict, S_LEN("listed"), buf->b_p_bl);
   tv_dict_add_nr(dict, S_LEN("changed"), bufIsChanged(buf));

src/nvim/testdir/test_bufwintabinfo.vim

@@ -139,3 +139,13 @@ function Test_get_win_options()
     set foldlevel=0
   endif
 endfunc
+
+func Test_getbufinfo_lines()
+  new Xfoo
+  call setline(1, ['a', 'bc', 'd'])
+  let bn = bufnr('%')
+  hide
+  call assert_equal(3, getbufinfo(bn)[0]["linecount"])
+  edit Xfoo
+  bw!
+endfunc