vim-patch:8.2.1905: the wininfo list may contain stale entries (#14884)

Problem:    The wininfo list may contain stale entries.
Solution:   When closing a window remove any other entry where the window
            pointer is NULL.
4882d98339

src/nvim/buffer.c

@@ -840,11 +840,7 @@ static void clear_wininfo(buf_T *buf)
   while (buf->b_wininfo != NULL) {
     wip = buf->b_wininfo;
     buf->b_wininfo = wip->wi_next;
-    if (wip->wi_optset) {
-      clear_winopt(&wip->wi_opt);
-      deleteFoldRecurse(buf, &wip->wi_folds);
-    }
-    xfree(wip);
+    free_wininfo(wip, buf);
   }
 }
 

src/nvim/window.c

@@ -4597,6 +4597,18 @@ static win_T *win_alloc(win_T *after, int hidden)
 }
 
 
+// Free one wininfo_T.
+void
+free_wininfo(wininfo_T *wip, buf_T *bp)
+{
+  if (wip->wi_optset) {
+    clear_winopt(&wip->wi_opt);
+    deleteFoldRecurse(bp, &wip->wi_folds);
+  }
+  xfree(wip);
+}
+
+
 /*
  * Remove window 'wp' from the window list and free the structure.
  */
@@ -4647,10 +4659,31 @@ win_free (
   /* Remove the window from the b_wininfo lists, it may happen that the
    * freed memory is re-used for another window. */
   FOR_ALL_BUFFERS(buf) {
-    for (wip = buf->b_wininfo; wip != NULL; wip = wip->wi_next)
-      if (wip->wi_win == wp)
+    for (wip = buf->b_wininfo; wip != NULL; wip = wip->wi_next) {
+      if (wip->wi_win == wp) {
+        wininfo_T *wip2;
+
+        // If there already is an entry with "wi_win" set to NULL it
+        // must be removed, it would never be used.
+        for (wip2 = buf->b_wininfo; wip2 != NULL; wip2 = wip2->wi_next) {
+          if (wip2->wi_win == NULL) {
+            if (wip2->wi_next != NULL) {
+              wip2->wi_next->wi_prev = wip2->wi_prev;
+            }
+            if (wip2->wi_prev == NULL) {
+              buf->b_wininfo = wip2->wi_next;
+            } else {
+              wip2->wi_prev->wi_next = wip2->wi_next;
+            }
+            free_wininfo(wip2, buf);
+            break;
+          }
+        }
+
         wip->wi_win = NULL;
       }
+    }
+  }
 
   clear_matches(wp);
 

test/functional/legacy/memory_usage_spec.lua

@@ -166,4 +166,36 @@ describe('memory usage', function()
     check_result({before=before, after=after, last=last},
                  pcall(ok, last.last < upper))
   end)
+
+  it('releases memory when closing windows when folds exist', function()
+    local pid = eval('getpid()')
+    source([[
+      new
+      " Insert lines
+      call nvim_buf_set_lines(0, 0, 0, v:false, repeat([''], 999))
+      " Create folds
+      normal! gg
+      for _ in range(500)
+        normal! zfjj
+      endfor
+    ]])
+    poke_eventloop()
+    local before = monitor_memory_usage(pid)
+    source([[
+      " Split and close window multiple times
+      for _ in range(1000)
+        split
+        close
+      endfor
+    ]])
+    poke_eventloop()
+    local after = monitor_memory_usage(pid)
+    source('bwipe!')
+    poke_eventloop()
+    -- Allow for an increase of 5% in memory usage, which accommodates minor fluctuation,
+    -- but is small enough that if memory were not released (prior to PR #14884), the test
+    -- would fail.
+    local upper = before.last * 1.05
+    check_result({before=before, after=after}, pcall(ok, after.last <= upper))
+  end)
 end)