fix(compiler): broken .git dir path resolution

Currently, in the file `lua/github-theme/init.lua`, the code
`util.join_paths(debug.getinfo(1).source:sub(2, -23), '.git')` returns
an absolute path ending in `**/lua/.git` which is not, and will never
be, a valid path to the `.git` directory. This means that recompilation
does not currently occur when the plugin updates or changes (unless user
config changes too) and that users may miss crucial updates (e.g. bug
fixes).

1. Fix bug by changing `util.join_paths(debug.getinfo(1).source:sub(2,
   -23), '.git')` to `debug.getinfo(1).source .. '/../../../.git'`, and
   then use luv's/libuv's `fs_stat()` to get the last modified time of
   this path. This change does not rely on any particular filenames
   existing in the path, but it still relies on a hard-coded depth. If
   the path does not exist or the stat is unsuccessful, force
   recompilation (as otherwise plugin updates could be missed by many
   users).

2. Use libuv/luv `fs_stat()` to get `.git` dir's mtime with nanosecond
   precision (NOTE: this function is only available by default in
   Neovim, not Vim, however, it appears that this plugin isn't
   compatible with Vim currently anyway, so this shouldn't be an issue).

3. Correctly handle `.git` files, as `.git` is not always a directory.

See #262

lua/github-theme/init.lua

@@ -1,3 +1,4 @@
+local uv = vim.loop
 local config = require('github-theme.config')
 
 local function read_file(filepath)
@@ -17,6 +18,16 @@ local function write_file(filepath, content)
   end
 end
 
+local function stat_file(path)
+  for _ = 1, 3 do
+    local stat = uv.fs_stat(path)
+    if stat then
+      return stat
+    end
+    uv.sleep(1)
+  end
+end
+
 local M = {}
 
 function M.reset()
@@ -94,11 +105,60 @@ M.setup = function(opts)
   local cached_path = util.join_paths(config.options.compile_path, 'cache')
   local cached = read_file(cached_path)
 
-  local git_path = util.join_paths(debug.getinfo(1).source:sub(2, -23), '.git')
-  local git = vim.fn.getftime(git_path)
-  local hash = require('github-theme.lib.hash')(opts) .. (git == -1 and git_path or git)
+  local git_mtime
+  local git_path = debug.getinfo(1).source
+
+  if (git_path or ''):find('^@.') then
+    git_path = git_path:sub(2) .. '/../../../.git'
+    local st = stat_file(git_path)
+
+    if not st then
+      goto skip
+    end
+
+    -- Handle a .git "file" (e.g. worktree or submodule)
+    if st.type == 'file' then
+      local f = io.open(git_path, 'r')
+
+      if not f then
+        goto skip
+      end
+
+      local gitdir_path = (f:read('*l') or ''):match('^gitdir: (.+)')
+      f:close()
+
+      if not gitdir_path then
+        goto skip
+      end
+
+      git_path = gitdir_path
+      st = stat_file(git_path)
+
+      if not st then
+        goto skip
+      end
+    end
+
+    local sec, nsec = st.mtime.sec, st.mtime.nsec or 0
+
+    if nsec == 1e9 then
+      sec = sec + 1
+      nsec = 0
+    end
+
+    git_mtime = ('%d.%09d'):format(sec, nsec)
+  end
+
+  ::skip::
+
+  local hash = ('%s %s'):format(
+    require('github-theme.lib.hash')(opts),
+    git_mtime or git_path
+  )
 
-  if cached ~= hash then
+  -- Force re-compile if .git dir could not be detected (plugin may have been
+  -- updated and we don't want to use a stale cache).
+  if cached ~= hash or not git_mtime then
     M.compile()
     write_file(cached_path, hash)
   end