Assistant: Use fstatat() while building FileProvider path cache

Using fstatat() allows the kernel to do relative path resolution as
opposed to absolute path resolution, which is significantly faster
and allows us to build the path cache sooner. :^)

Userland/Applications/Assistant/Providers.cpp

@@ -6,8 +6,10 @@
 
 #include "Providers.h"
 #include "FuzzyMatch.h"
+#include <AK/LexicalPath.h>
 #include <AK/URL.h>
 #include <LibCore/DirIterator.h>
+#include <LibCore/ElapsedTimer.h>
 #include <LibCore/File.h>
 #include <LibCore/StandardPaths.h>
 #include <LibDesktop/Launcher.h>
@@ -18,6 +20,7 @@
 #include <LibJS/Parser.h>
 #include <LibJS/Runtime/GlobalObject.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <serenity.h>
 #include <spawn.h>
 #include <unistd.h>
@@ -151,28 +154,34 @@ void FileProvider::build_filesystem_cache()
  m_work_queue.enqueue("/");
 
  Threading::BackgroundAction<int>::create([this](auto&) {
+ String slash = "/";
+ Core::ElapsedTimer timer;
+ timer.start();
  while (!m_work_queue.is_empty()) {
- auto start = m_work_queue.dequeue();
- Core::DirIterator di(start, Core::DirIterator::SkipDots);
+ auto base_directory = m_work_queue.dequeue();
+ Core::DirIterator di(base_directory, Core::DirIterator::SkipDots);
 
  while (di.has_next()) {
- auto path = di.next_full_path();
+ auto path = di.next_path();
  struct stat st = {};
- if (lstat(path.characters(), &st) < 0) {
- perror("stat");
+ if (fstatat(di.fd(), path.characters(), &st, AT_SYMLINK_) < 0) {
+ perror("fstatat");
  continue;
  }
 
  if (S_ISLNK(st.st_mode))
  continue;
 
- m_full_path_cache.append(path);
+ auto full_path = LexicalPath::join(slash, base_directory, path).string();
+
+ m_full_path_cache.append(full_path);
 
  if (S_ISDIR(st.st_mode)) {
- m_work_queue.enqueue(path);
+ m_work_queue.enqueue(full_path);
  }
  }
  }
+ dbgln("Built cache in {} ms", timer.elapsed());
 
  return 0; }, [this](auto) { m_building_cache = false; });
 }