vim-patch:8.0.1160: getting tab-local variable fails after closing window

Problem:    Getting tab-local variable fails after closing window.
Solution:   set tp_firstwin and tp_lastwin. (Jason Franklin, closes vim/vim#2170)
816968defc

src/nvim/eval.c

@@ -10222,7 +10222,8 @@ static void f_gettabvar(typval_T *argvars, typval_T *rettv, FunPtr fptr)
   if (tp != NULL && varname != NULL) {
     // Set tp to be our tabpage, temporarily.  Also set the window to the
     // first window in the tabpage, otherwise the window is not valid.
-    win_T *window = tp->tp_firstwin == NULL ? firstwin : tp->tp_firstwin;
+    win_T *window = tp == curtab || tp->tp_firstwin == NULL ? firstwin
+                                                            : tp->tp_firstwin;
     if (switch_win(&oldcurwin, &oldtabpage, window, tp, true) == OK) {
       // look up the variable
       // Let gettabvar({nr}, "") return the "t:" dictionary.

src/nvim/testdir/test_getvar.vim

@@ -86,3 +86,19 @@ func Test_var()
   call assert_equal(1, gettabwinvar(2, 3, '&nux', 1))
   tabonly
 endfunc
+
+" It was discovered that "gettabvar()" would fail if called from within the
+" tabline when the user closed a window.  This test confirms the fix.
+func Test_gettabvar_in_tabline()
+  let t:var_str = 'value'
+
+  set tabline=%{assert_equal('value',gettabvar(1,'var_str'))}
+  set showtabline=2
+
+  " Simulate the user opening a split (which becomes window #1) and then
+  " closing the split, which triggers the redrawing of the tabline.
+  leftabove split
+  redrawstatus!
+  close
+  redrawstatus!
+endfunc

src/nvim/window.c

@@ -3970,18 +3970,20 @@ win_remove (
     tabpage_T *tp                /* tab page "win" is in, NULL for current */
 )
 {
-  if (wp->w_prev != NULL)
+  if (wp->w_prev != NULL) {
     wp->w_prev->w_next = wp->w_next;
-  else if (tp == NULL)
+  } else if (tp == NULL) {
-    firstwin = wp->w_next;
+    firstwin = curtab->tp_firstwin = wp->w_next;
-  else
+  } else {
     tp->tp_firstwin = wp->w_next;
-  if (wp->w_next != NULL)
+  }
+  if (wp->w_next != NULL) {
     wp->w_next->w_prev = wp->w_prev;
-  else if (tp == NULL)
+  } else if (tp == NULL) {
-    lastwin = wp->w_prev;
+    lastwin = curtab->tp_lastwin = wp->w_prev;
-  else
+  } else {
     tp->tp_lastwin = wp->w_prev;
+  }
 }
 
 /*