fix(fs): prevent endless EPERM when deleting a parent directory #42635

Problem:
On Windows, libuv emits endless EPERM errors when another process
deletes the parent directory of an open file, causing nvim to hang.

Solution:
Ideally, bump libuv version once the issue is fixed upstream.
For now, we have to stop handle immediately to prevent endless EPERM
errors from starving the debounced cleanup callback in autoread.lua.

runtime/lua/vim/_watch.lua

@@ -1,5 +1,6 @@
 local uv = vim.uv
 local log = vim.log.new({ name = 'nvim-watch' })
+local is_win = package.config:sub(1, 1) == '\\'
 
 local M = {}
 
@@ -451,6 +452,10 @@ local function watch(path, opts, callback)
     if events.rename then
       local _, staterr, staterrname = uv.fs_stat(fullpath)
       if staterrname == 'ENOENT' then
+        -- stop handle to prevent endless EPERM errors (neovim#41851, libuv#5399)
+        if is_win and not watching_dir then
+          handle:stop()
+        end
         change_type = M.FileChangeType.Deleted
       else
         if staterr then

test/functional/lua/watch_spec.lua

@@ -389,6 +389,62 @@ describe('vim._watch', function()
     }, result)
   end)
 
+  it('watch() stops when the parent directory of watched file is deleted #41851', function()
+    local root_dir = t.tmpname(false)
+    t.finally(function()
+      n.rmdir(root_dir)
+    end)
+    n.mkdir_p(root_dir)
+    local file = ('%s/file'):format(root_dir)
+    vim.fn.writefile({ 'x' }, file)
+
+    exec_lua(
+      [[
+      local f = ...
+      _G.events = {}
+      _G.errors = {}
+      _G.cancel = vim._watch.watch(f, {
+        on_error = function(err)
+          _G.errors[#_G.errors + 1] = err
+        end,
+      }, function(p, change_type)
+        _G.events[#_G.events + 1] = { path = p, change_type = change_type }
+      end)
+      vim.wait(0)
+      ]],
+      file
+    )
+
+    assert(vim.uv.fs_unlink(file))
+    assert(vim.uv.fs_rmdir(root_dir))
+
+    exec_lua([[
+      assert(
+        vim.wait(3000, function()
+          return #_G.events >= 1
+        end), 'Timed out waiting for event')
+    ]])
+    eq({
+      path = file,
+      change_type = exec_lua([[return vim._watch.FileChangeType.Deleted]]),
+    }, exec_lua [=[return _G.events[#_G.events]]=])
+
+    eq(
+      not is_os('win'),
+      exec_lua(function()
+        local active
+        vim.uv.walk(function(handle)
+          if handle:get_type() == 'fs_event' then
+            active = handle:is_active()
+          end
+        end)
+        return active
+      end)
+    )
+    exec_lua [[_G.cancel()]]
+    eq(0, exec_lua [[return vim._watch.active().watch]])
+  end)
+
   it('watchdirs() tracks directories for matching files until cancelled', function()
     local root_dir = t.tmpname(false)
     n.mkdir_p(root_dir .. '/src')