oil: don't show git ignored files and folders

lua/plugins/oil.lua

@@ -1,3 +1,27 @@
+local git_ignored = setmetatable({}, {
+  __index = function(self, key)
+    local proc = vim.system(
+      { "git", "ls-files", "--ignored", "--exclude-standard", "--others", "--directory" },
+      {
+        cwd = key,
+        text = true,
+      }
+    )
+    local result = proc:wait()
+    local ret = {}
+    if result.code == 0 then
+      for line in vim.gsplit(result.stdout, "\n", { plain = true, trimempty = true }) do
+        -- Remove trailing slash
+        line = line:gsub("/$", "")
+        table.insert(ret, line)
+      end
+    end
+
+    rawset(self, key, ret)
+    return ret
+  end,
+})
+
 require('oil').setup({
     default_file_explorer = true,
     -- Id is automatically added at the beginning, and name at the end
@@ -61,8 +85,16 @@ require('oil').setup({
         -- Show files and directories that start with "."
         show_hidden = false,
         -- This function defines what is considered a "hidden" file
-        is_hidden_file = function(name, bufnr)
-            return vim.startswith(name, ".")
+        is_hidden_file = function(name, _)
+            if vim.startswith(name, ".") then
+                return true
+            end
+            local dir = require("oil").get_current_dir()
+            -- if no local directory (e.g. for ssh connections), always show
+            if not dir then
+                return false
+            end
+            return vim.list_contains(git_ignored[dir], name)
         end,
         -- This function defines what will never be shown, even when `show_hidden` is set
         is_always_hidden = function(name, bufnr)