vim-patch:8.2.4731: the changelist index is not remembered per buffer

Problem:    The changelist index is not remembered per buffer.
Solution:   Keep the changelist index per window and buffer. (closes vim/vim#10135,
            closes vim/vim#2173)
https://github.com/vim/vim/commit/db0ea7f2b00c84d84f188c9e9953c4f1887528e7

Cherry-pick FOR_ALL_BUF_WININFO from patch 8.2.0500.
Cherry-pick test_changelist.vim change from patch 8.2.3795.

5 files changed, 55 insertions, 13 deletions

diff --git a/src/nvim/buffer.c b/src/nvim/buffer.c
index 4830b200af..10ce893fe8 100644
--- a/src/nvim/buffer.c
+++ b/src/nvim/buffer.c
@@ -2483,6 +2483,9 @@ void buflist_setfpos(buf_T *const buf, win_T *const win, linenr_T lnum, colnr_T
       wip->wi_mark.view = mark_view_make(win->w_topline, wip->wi_mark.mark);
     }
   }
+  if (win != NULL) {
+    wip->wi_changelistidx = win->w_changelistidx;
+  }
   if (copy_options && win != NULL) {
     // Save the window-specific option values.
     copy_winopt(&win->w_onebuf_opt, &wip->wi_opt);
@@ -2586,6 +2589,9 @@ void get_winopts(buf_T *buf)
   } else {
     copy_winopt(&curwin->w_allbuf_opt, &curwin->w_onebuf_opt);
   }
+  if (wip != NULL) {
+    curwin->w_changelistidx = wip->wi_changelistidx;
+  }
 
   if (curwin->w_float_config.style == kWinStyleMinimal) {
     didset_window_options(curwin);
diff --git a/src/nvim/buffer_defs.h b/src/nvim/buffer_defs.h
index 8c70765d30..c052c2fdfd 100644
--- a/src/nvim/buffer_defs.h
+++ b/src/nvim/buffer_defs.h
@@ -289,6 +289,7 @@ struct wininfo_S {
   winopt_T wi_opt;              // local window options
   bool wi_fold_manual;          // copy of w_fold_manual
   garray_T wi_folds;            // clone of w_folds
+  int wi_changelistidx;         // copy of w_changelistidx
 };
 
 /*
diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index 5ee499e006..dac6bb6e34 100644
--- a/src/nvim/eval/funcs.c
+++ b/src/nvim/eval/funcs.c
@@ -2824,13 +2824,23 @@ static void f_getchangelist(typval_T *argvars, typval_T *rettv, FunPtr fptr)
 
   list_T *const l = tv_list_alloc(buf->b_changelistlen);
   tv_list_append_list(rettv->vval.v_list, l);
-  // The current window change list index tracks only the position in the
-  // current buffer change list. For other buffers, use the change list
-  // length as the current index.
-  tv_list_append_number(rettv->vval.v_list,
-                        (buf == curwin->w_buffer)
-                        ? curwin->w_changelistidx
-                        : buf->b_changelistlen);
+  // The current window change list index tracks only the position for the
+  // current buffer. For other buffers use the stored index for the current
+  // window, or, if that's not available, the change list length.
+  int changelistindex;
+  if (buf == curwin->w_buffer) {
+    changelistindex = curwin->w_changelistidx;
+  } else {
+    wininfo_T *wip;
+
+    FOR_ALL_BUF_WININFO(buf, wip) {
+      if (wip->wi_win == curwin) {
+        break;
+      }
+    }
+    changelistindex = wip != NULL ? wip->wi_changelistidx : buf->b_changelistlen;
+  }
+  tv_list_append_number(rettv->vval.v_list, (varnumber_T)changelistindex);
 
   for (int i = 0; i < buf->b_changelistlen; i++) {
     if (buf->b_changelist[i].mark.lnum == 0) {
diff --git a/src/nvim/globals.h b/src/nvim/globals.h
index b585467bd0..9946085703 100644
--- a/src/nvim/globals.h
+++ b/src/nvim/globals.h
@@ -467,6 +467,9 @@ EXTERN buf_T *curbuf INIT(= NULL);    // currently active buffer
 #define FOR_ALL_BUFFERS_BACKWARDS(buf) \
   for (buf_T *buf = lastbuf; buf != NULL; buf = buf->b_prev)
 
+#define FOR_ALL_BUF_WININFO(buf, wip) \
+  for ((wip) = (buf)->b_wininfo; (wip) != NULL; (wip) = (wip)->wi_next)   // NOLINT
+
 // Iterate through all the signs placed in a buffer
 #define FOR_ALL_SIGNS_IN_BUF(buf, sign) \
   for ((sign) = (buf)->b_signlist; (sign) != NULL; (sign) = (sign)->se_next)   // NOLINT
diff --git a/src/nvim/testdir/test_changelist.vim b/src/nvim/testdir/test_changelist.vim
index 3741f32e69..f429968218 100644
--- a/src/nvim/testdir/test_changelist.vim
+++ b/src/nvim/testdir/test_changelist.vim
@@ -1,12 +1,30 @@
 " Tests for the changelist functionality
 
 " Tests for the getchangelist() function
-func Test_getchangelist()
-  if !has("jumplist")
-    return
-  endif
+func Test_changelist_index()
+  edit Xfile1.txt
+  exe "normal iabc\<C-G>u\ndef\<C-G>u\nghi"
+  call assert_equal(3, getchangelist('%')[1])
+  " Move one step back in the changelist.
+  normal 2g;
+
+  hide edit Xfile2.txt
+  exe "normal iabcd\<C-G>u\ndefg\<C-G>u\nghij"
+  call assert_equal(3, getchangelist('%')[1])
+  " Move to the beginning of the changelist.
+  normal 99g;
+
+  " Check the changelist indices.
+  call assert_equal(0, getchangelist('%')[1])
+  call assert_equal(1, getchangelist('#')[1])
 
   bwipe!
+  call delete('Xfile1.txt')
+  call delete('Xfile2.txt')
+endfunc
+
+func Test_getchangelist()
+  bwipe!
   enew
   call assert_equal([], 10->getchangelist())
   call assert_equal([[], 0], getchangelist())
@@ -15,6 +33,7 @@ func Test_getchangelist()
   call writefile(['line1', 'line2', 'line3'], 'Xfile2.txt')
 
   edit Xfile1.txt
+  let buf_1 = bufnr()
   exe "normal 1Goline\<C-G>u1.1"
   exe "normal 3Goline\<C-G>u2.1"
   exe "normal 5Goline\<C-G>u3.1"
@@ -26,6 +45,7 @@ func Test_getchangelist()
 	      \ getchangelist('%'))
 
   hide edit Xfile2.txt
+  let buf_2 = bufnr()
   exe "normal 1GOline\<C-G>u1.0"
   exe "normal 2Goline\<C-G>u2.0"
   call assert_equal([[
@@ -37,10 +57,12 @@ func Test_getchangelist()
   call assert_equal([[
 	      \ {'lnum' : 2, 'col' : 4, 'coladd' : 0},
 	      \ {'lnum' : 4, 'col' : 4, 'coladd' : 0},
-	      \ {'lnum' : 6, 'col' : 4, 'coladd' : 0}], 3], getchangelist(2))
+	      \ {'lnum' : 6, 'col' : 4, 'coladd' : 0}], 2],
+	      \ getchangelist(buf_1))
   call assert_equal([[
 	      \ {'lnum' : 1, 'col' : 6, 'coladd' : 0},
-	      \ {'lnum' : 3, 'col' : 6, 'coladd' : 0}], 2], getchangelist(3))
+	      \ {'lnum' : 3, 'col' : 6, 'coladd' : 0}], 2],
+	      \ getchangelist(buf_2))
 
   bwipe!
   call delete('Xfile1.txt')