feat(lsp): drop fswatch, use inotifywait (#29374)

This patch replaces fswatch with inotifywait from inotify-toools:

https://github.com/inotify-tools/inotify-tools

fswatch takes ~1min to set up recursively for the Samba source code
directory. inotifywait needs less than a second to do the same thing.

https://github.com/emcrisostomo/fswatch/issues/321

Also it fswatch seems to be unmaintained in the meantime.

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>

7 files changed, 54 insertions, 53 deletions

diff --git a/.github/scripts/install_deps.sh b/.github/scripts/install_deps.sh
index 66f418eb10..b90a84fc24 100755
--- a/.github/scripts/install_deps.sh
+++ b/.github/scripts/install_deps.sh
@@ -30,7 +30,7 @@ if [[ $os == Linux ]]; then
   fi
 
   if [[ -n $TEST ]]; then
-    sudo apt-get install -y locales-all cpanminus attr libattr1-dev gdb fswatch
+    sudo apt-get install -y locales-all cpanminus attr libattr1-dev gdb inotify-tools
 
     # Use default CC to avoid compilation problems when installing Python modules
     CC=cc python3 -m pip -q install --user --upgrade pynvim
diff --git a/runtime/doc/lua.txt b/runtime/doc/lua.txt
index 39a047cbab..dfaf666874 100644
--- a/runtime/doc/lua.txt
+++ b/runtime/doc/lua.txt
@@ -543,16 +543,19 @@ Example: File-change detection                                    *watch-file*
     vim.api.nvim_command(
       "command! -nargs=1 Watch call luaeval('watch_file(_A)', expand('<args>'))")
 <
-                                                         *fswatch-limitations*
-When on Linux and using fswatch, you may need to increase the maximum number
-of `inotify` watches and queued events as the default limit can be too low. To
-increase the limit, run: >sh
-    sysctl fs.inotify.max_user_watches=100000
-    sysctl fs.inotify.max_queued_events=100000
+                                                         *inotify-limitations*
+When on Linux you may need to increase the maximum number of `inotify` watches
+and queued events as the default limit can be too low. To increase the limit,
+run: >sh
+    sysctl fs.inotify.max_user_watches=494462
 <
-This will increase the limit to 100000 watches and queued events. These lines
+This will increase the limit to 494462 watches and queued events. These lines
 can be added to `/etc/sysctl.conf` to make the changes persistent.
 
+Note that each watch is a structure in the Kernel, thus available memory is
+also a bottleneck for using inotify. In fact, a watch can take up to 1KB of
+space. This means a million watches could result in 1GB of extra RAM usage.
+
 Example: TCP echo-server                                          *tcp-server*
     1. Save this code to a file.
     2. Execute it with ":luafile %".
diff --git a/runtime/lua/vim/_watch.lua b/runtime/lua/vim/_watch.lua
index 02b3f536c2..40f18ce5b0 100644
--- a/runtime/lua/vim/_watch.lua
+++ b/runtime/lua/vim/_watch.lua
@@ -227,11 +227,12 @@ end
 --- @param data string
 --- @param opts vim._watch.Opts?
 --- @param callback vim._watch.Callback
-local function fswatch_output_handler(data, opts, callback)
+local function on_inotifywait_output(data, opts, callback)
   local d = vim.split(data, '%s+')
 
   -- only consider the last reported event
-  local fullpath, event = d[1], d[#d]
+  local path, event, file = d[1], d[2], d[#d]
+  local fullpath = vim.fs.joinpath(path, file)
 
   if skip(fullpath, opts) then
     return
@@ -240,20 +241,16 @@ local function fswatch_output_handler(data, opts, callback)
   --- @type integer
   local change_type
 
-  if event == 'Created' then
+  if event == 'CREATE' then
     change_type = M.FileChangeType.Created
-  elseif event == 'Removed' then
+  elseif event == 'DELETE' then
     change_type = M.FileChangeType.Deleted
-  elseif event == 'Updated' then
+  elseif event == 'MODIFY' then
     change_type = M.FileChangeType.Changed
-  elseif event == 'Renamed' then
-    local _, staterr, staterrname = uv.fs_stat(fullpath)
-    if staterrname == 'ENOENT' then
-      change_type = M.FileChangeType.Deleted
-    else
-      assert(not staterr, staterr)
-      change_type = M.FileChangeType.Created
-    end
+  elseif event == 'MOVED_FROM' then
+    change_type = M.FileChangeType.Deleted
+  elseif event == 'MOVED_TO' then
+    change_type = M.FileChangeType.Created
   end
 
   if change_type then
@@ -265,24 +262,22 @@ end
 --- @param opts vim._watch.Opts?
 --- @param callback vim._watch.Callback Callback for new events
 --- @return fun() cancel Stops the watcher
-function M.fswatch(path, opts, callback)
-  -- debounce isn't the same as latency but close enough
-  local latency = 0.5 -- seconds
-  if opts and opts.debounce then
-    latency = opts.debounce / 1000
-  end
-
+function M.inotify(path, opts, callback)
   local obj = vim.system({
-    'fswatch',
-    '--event=Created',
-    '--event=Removed',
-    '--event=Updated',
-    '--event=Renamed',
-    '--event-flags',
+    'inotifywait',
+    '--quiet', -- suppress startup messages
+    '--no-dereference', -- don't follow symlinks
+    '--monitor', -- keep listening for events forever
     '--recursive',
-    '--latency=' .. tostring(latency),
-    '--exclude',
-    '/.git/',
+    '--event',
+    'create',
+    '--event',
+    'delete',
+    '--event',
+    'modify',
+    '--event',
+    'move',
+    '@.git', -- ignore git directory
     path,
   }, {
     stderr = function(err, data)
@@ -292,11 +287,11 @@ function M.fswatch(path, opts, callback)
 
       if data and #vim.trim(data) > 0 then
         vim.schedule(function()
-          if vim.fn.has('linux') == 1 and vim.startswith(data, 'Event queue overflow') then
-            data = 'inotify(7) limit reached, see :h fswatch-limitations for more info.'
+          if vim.fn.has('linux') == 1 and vim.startswith(data, 'Failed to watch') then
+            data = 'inotify(7) limit reached, see :h inotify-limitations for more info.'
           end
 
-          vim.notify('fswatch: ' .. data, vim.log.levels.ERROR)
+          vim.notify('inotify: ' .. data, vim.log.levels.ERROR)
         end)
       end
     end,
@@ -306,7 +301,7 @@ function M.fswatch(path, opts, callback)
       end
 
       for line in vim.gsplit(data or '', '\n', { plain = true, trimempty = true }) do
-        fswatch_output_handler(line, opts, callback)
+        on_inotifywait_output(line, opts, callback)
       end
     end,
     -- --latency is locale dependent but tostring() isn't and will always have '.' as decimal point.
diff --git a/runtime/lua/vim/lsp/_watchfiles.lua b/runtime/lua/vim/lsp/_watchfiles.lua
index 49328fbe9b..98e9818bcd 100644
--- a/runtime/lua/vim/lsp/_watchfiles.lua
+++ b/runtime/lua/vim/lsp/_watchfiles.lua
@@ -9,8 +9,8 @@ local M = {}
 
 if vim.fn.has('win32') == 1 or vim.fn.has('mac') == 1 then
   M._watchfunc = watch.watch
-elseif vim.fn.executable('fswatch') == 1 then
-  M._watchfunc = watch.fswatch
+elseif vim.fn.executable('inotifywait') == 1 then
+  M._watchfunc = watch.inotify
 else
   M._watchfunc = watch.watchdirs
 end
diff --git a/runtime/lua/vim/lsp/health.lua b/runtime/lua/vim/lsp/health.lua
index ffe595ab37..18066a84db 100644
--- a/runtime/lua/vim/lsp/health.lua
+++ b/runtime/lua/vim/lsp/health.lua
@@ -90,8 +90,8 @@ local function check_watcher()
     watchfunc_name = 'libuv-watch'
   elseif watchfunc == vim._watch.watchdirs then
     watchfunc_name = 'libuv-watchdirs'
-  elseif watchfunc == vim._watch.fswatch then
-    watchfunc_name = 'fswatch'
+  elseif watchfunc == vim._watch.inotifywait then
+    watchfunc_name = 'inotifywait'
   else
     local nm = debug.getinfo(watchfunc, 'S').source
     watchfunc_name = string.format('Custom (%s)', nm)
@@ -99,7 +99,7 @@ local function check_watcher()
 
   report_info('File watch backend: ' .. watchfunc_name)
   if watchfunc_name == 'libuv-watchdirs' then
-    report_warn('libuv-watchdirs has known performance issues. Consider installing fswatch.')
+    report_warn('libuv-watchdirs has known performance issues. Consider installing inotify-tools.')
   end
 end
 
diff --git a/test/functional/lua/watch_spec.lua b/test/functional/lua/watch_spec.lua
index bd8faadf5b..3d2dda716e 100644
--- a/test/functional/lua/watch_spec.lua
+++ b/test/functional/lua/watch_spec.lua
@@ -23,10 +23,13 @@ describe('vim._watch', function()
 
   local function run(watchfunc)
     it('detects file changes (watchfunc=' .. watchfunc .. '())', function()
-      if watchfunc == 'fswatch' then
+      if watchfunc == 'inotify' then
         skip(is_os('win'), 'not supported on windows')
         skip(is_os('mac'), 'flaky test on mac')
-        skip(not is_ci() and n.fn.executable('fswatch') == 0, 'fswatch not installed and not on CI')
+        skip(
+          not is_ci() and n.fn.executable('inotifywait') == 0,
+          'inotify-tools not installed and not on CI'
+        )
       end
 
       if watchfunc == 'watch' then
@@ -123,5 +126,5 @@ describe('vim._watch', function()
 
   run('watch')
   run('watchdirs')
-  run('fswatch')
+  run('inotify')
 end)
diff --git a/test/functional/plugin/lsp_spec.lua b/test/functional/plugin/lsp_spec.lua
index 0630df65d5..2b8a7aed9e 100644
--- a/test/functional/plugin/lsp_spec.lua
+++ b/test/functional/plugin/lsp_spec.lua
@@ -5128,12 +5128,12 @@ describe('LSP', function()
       it(
         string.format('sends notifications when files change (watchfunc=%s)', watchfunc),
         function()
-          if watchfunc == 'fswatch' then
+          if watchfunc == 'inotify' then
             skip(is_os('win'), 'not supported on windows')
             skip(is_os('mac'), 'flaky test on mac')
             skip(
-              not is_ci() and fn.executable('fswatch') == 0,
-              'fswatch not installed and not on CI'
+              not is_ci() and fn.executable('inotifywait') == 0,
+              'inotify-tools not installed and not on CI'
             )
           end
 
@@ -5265,7 +5265,7 @@ describe('LSP', function()
 
     test_filechanges('watch')
     test_filechanges('watchdirs')
-    test_filechanges('fswatch')
+    test_filechanges('inotify')
 
     it('correctly registers and unregisters', function()
       local root_dir = '/some_dir'