vim-patch:8.2.4719: ">" marker sometimes not displayed in the jumplist (#18056)

Problem:    ">" marker sometimes not displayed in the jumplist.
Solution:   If the buffer no longer exists show "-invalid-". (Christian
            Brabandt, closes vim/vim#10131, closes vim/vim#10100)
a0f659c76e

Add a modeline to test_jumplist.vim

src/nvim/mark.c

@@ -844,6 +844,11 @@ void ex_jumps(exarg_T *eap)
     if (curwin->w_jumplist[i].fmark.mark.lnum != 0) {
       name = fm_getname(&curwin->w_jumplist[i].fmark, 16);
 
+      // Make sure to output the current indicator, even when on an wiped
+      // out buffer.  ":filter" may still skip it.
+      if (name == NULL && i == curwin->w_jumplistidx) {
+        name = vim_strsave((char_u *)"-invalid-");
+      }
       // apply :filter /pat/ or file name not available
       if (name == NULL || message_filtered(name)) {
         xfree(name);

src/nvim/testdir/test_alot.vim

@@ -16,7 +16,6 @@ source test_fnamemodify.vim
 source test_ga.vim
 source test_glob2regpat.vim
 source test_global.vim
-source test_jumps.vim
 source test_lispwords.vim
 source test_menu.vim
 source test_move.vim

src/nvim/testdir/test_jumplist.vim

@@ -64,3 +64,44 @@ func Test_getjumplist()
 
   call delete("Xtest")
 endfunc
+
+func Test_jumplist_invalid()
+  new
+  clearjumps
+  " put some randome text
+  put ='a'
+  let prev = bufnr('%')
+  setl nomodified bufhidden=wipe
+  e XXJumpListBuffer
+  let bnr = bufnr('%')
+  " 1) empty jumplist
+  let expected = [[
+   \ {'lnum': 2, 'bufnr': prev, 'col': 0, 'coladd': 0}], 1]
+  call assert_equal(expected, getjumplist())
+  let jumps = execute(':jumps')
+  call assert_equal('>', jumps[-1:])
+  " now jump back
+  exe ":norm! \<c-o>"
+  let expected = [[
+    \ {'lnum': 2, 'bufnr': prev, 'col': 0, 'coladd': 0},
+    \ {'lnum': 1, 'bufnr': bnr,  'col': 0, 'coladd': 0}], 0]
+  call assert_equal(expected, getjumplist())
+  let jumps = execute(':jumps')
+  call assert_match('>  0     2    0 -invalid-', jumps)
+endfunc
+
+" Test for '' mark in an empty buffer
+
+func Test_empty_buffer()
+  new
+  insert
+a
+b
+c
+d
+.
+  call assert_equal(1, line("''"))
+  bwipe!
+endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab

src/nvim/testdir/test_jumps.vim

@@ -1,11 +0,0 @@
-func Test_empty_buffer()
-  new
-  insert
-a
-b
-c
-d
-.
-  call assert_equal(1, line("''"))
-  bwipe!
-endfunc