fix(watcher): improve debounce to be unique per file

lua/gitsigns/debounce.lua

@@ -7,14 +7,21 @@ local M = {}
 --- @generic F: function
 --- @param ms number Timeout in ms
 --- @param fn F Function to debounce
+--- @param hash? fun(...): any Function that determines id from arguments to fn
 --- @return F Debounced function.
-function M.debounce_trailing(ms, fn)
-  local timer = assert(uv.new_timer())
+function M.debounce_trailing(ms, fn, hash)
+  local running = {} --- @type table<any,uv.uv_timer_t>
   return function(...)
+    local id = hash and hash(...) or true
+    if running[id] == nil then
+      running[id] = assert(uv.new_timer())
+    end
+    local timer = running[id]
     local argv = { ... }
     timer:start(ms, 0, function()
       timer:stop()
-      fn(unpack(argv))
+      running[id] = nil
+      fn(unpack(argv, 1, table.maxn(argv)))
     end)
   end
 end

lua/gitsigns/watcher.lua

@@ -59,7 +59,9 @@ local function handle_moved(bufnr, old_relpath)
   dprintf('%s buffer %d from %s to %s', msg, bufnr, old_name, bcache.file)
 end
 
-local watch_gitdir_handler = async.void(function(bufnr)
+local handler = async.void(function(bufnr, file)
+  local __FUNC__ = 'watcher_handler'
+  dprint(file)
   buf_check(bufnr)
 
   local git_obj = cache[bufnr].git_obj
@@ -83,11 +85,28 @@ local watch_gitdir_handler = async.void(function(bufnr)
     buf_check(bufnr)
   end
 
-  cache[bufnr]:invalidate()
+  local bcache = cache[bufnr]
+
+  if not bcache.base and file == 'index' then
+    bcache.compare_text = nil
+  end
+
+  if file == 'HEAD' then
+    bcache.compare_text_head = nil
+  end
+
+  bcache.hunks = nil
+  bcache.hunks_staged = nil
 
   require('gitsigns.manager').update(bufnr)
 end)
 
+local function handler_hash(bufnr, filename)
+  return string.format('%d:%s', bufnr, filename)
+end
+
+local handler_db = debounce_trailing(200, handler, handler_hash)
+
 -- vim.inspect but on one line
 --- @param x any
 --- @return string
@@ -97,14 +116,15 @@ end
 
 local M = {}
 
+local WATCH_IGNORE = {
+  ORIG_HEAD = true,
+  FETCH_HEAD = true
+}
+
 --- @param bufnr integer
 --- @param gitdir string
 --- @return uv.uv_fs_event_t
 function M.watch_gitdir(bufnr, gitdir)
-  -- Setup debounce as we create the luv object so the debounce is independent
-  -- to each watcher
-  local watch_gitdir_handler_db = debounce_trailing(200, watch_gitdir_handler)
-
   dprintf('Watching git dir')
   local w = assert(uv.new_fs_event())
   w:start(gitdir, {}, function(err, filename, events)
@@ -119,14 +139,14 @@ function M.watch_gitdir(bufnr, gitdir)
     -- The luv docs say filename is passed as a string but it has been observed
     -- to sometimes be nil.
     --    https://github.com/lewis6991/gitsigns.nvim/issues/848
-    if filename == nil or vim.endswith(filename, '.lock') then
+    if filename == nil or WATCH_IGNORE[filename] or vim.endswith(filename, '.lock') then
       dprintf('%s (ignoring)', info)
       return
     end
 
     dprint(info)
 
-    watch_gitdir_handler_db(bufnr)
+    handler_db(bufnr, filename)
   end)
   return w
 end