[vcpkg] Make Filesystem::remove_all faster #7570

I added benchmarks to measure how fast the parallel remove_all code was
-- it turns out, about 3x slower than stdfs::remove_all. Since this was
the case, I removed all of the parallelism and rewrote it serially, and
ended up about 30% faster than stdfs::remove_all (in addition to
supporting symlinks).

In addition, I did the following three orthogonal changes:
  - simplified the work queue, basing it on Billy O'Neal's idea
  - Fix warnings on older versions of compilers in tests, by splitting
    the pragmas out of pch.h.
  - Ran clang-format on some files

In fixing up remove_all, the following changes were made:
  - On Windows, regular symlinks and directory symlinks are distinct;
    as an example, to remove directory symlinks (and junctions, for that
    matter), one must use RemoveDirectory. Only on Windows, I added new
    `file_type` and `file_status` types, with `file_type` including a new
    `directory_symlink` enumerator, and `file_status` being exactly the
    same as the old one except using the new `file_type`. On Unix, I
    didn't make that change since they don't make a distinction.
  - I added new `symlink_status` and `status` functions which use the
    new `file_status` on Windows.
  - I made `Filesystem::exists` call `fs::exists(status(p))`, as opposed
    to the old version which called `stdfs::exists` directly.
  - Added benchmarks to `vcpkg-test/files.cpp`. They test the
    performance of `remove_all` on small directories (~20 files), with
    symlinks and without, and on large directories (~2000 files), with
    symlinks and without.

1 files changed, 15 insertions, 11 deletions

diff --git a/toolsrc/src/vcpkg-test/util.cpp b/toolsrc/src/vcpkg-test/util.cpp
index 5359b0fad..384954b4e 100644
--- a/toolsrc/src/vcpkg-test/util.cpp
+++ b/toolsrc/src/vcpkg-test/util.cpp
@@ -74,14 +74,14 @@ namespace vcpkg::Test
         return m_ret.value_or_exit(VCPKG_LINE_INFO);
     }
 
-    static bool system_allows_symlinks()
+    static AllowSymlinks internal_can_create_symlinks() noexcept
     {
 #if FILESYSTEM_SYMLINK == FILESYSTEM_SYMLINK_NONE
-        return false;
+        return AllowSymlinks::No;
 #elif FILESYSTEM_SYMLINK == FILESYSTEM_SYMLINK_UNIX
-        return true;
+        return AllowSymlinks::Yes;
 #elif !defined(_WIN32) // FILESYSTEM_SYMLINK == FILESYSTEM_SYMLINK_STD
-        return true;
+        return AllowSymlinks::Yes;
 #else
         HKEY key;
         bool allow_symlinks = true;
@@ -97,11 +97,14 @@ namespace vcpkg::Test
 
         if (status == ERROR_SUCCESS) RegCloseKey(key);
 
-        return allow_symlinks;
+        return allow_symlinks ? AllowSymlinks::Yes : AllowSymlinks::No;
 #endif
     }
+    const static AllowSymlinks CAN_CREATE_SYMLINKS = internal_can_create_symlinks();
 
-    static fs::path internal_temporary_directory()
+    AllowSymlinks can_create_symlinks() noexcept { return CAN_CREATE_SYMLINKS; }
+
+    static fs::path internal_base_temporary_directory()
     {
 #if defined(_WIN32)
         wchar_t* tmp = static_cast<wchar_t*>(std::calloc(32'767, 2));
@@ -121,8 +124,9 @@ namespace vcpkg::Test
 #endif
     }
 
-    const bool SYMLINKS_ALLOWED = system_allows_symlinks();
-    const fs::path TEMPORARY_DIRECTORY = internal_temporary_directory();
+    const static fs::path BASE_TEMPORARY_DIRECTORY = internal_base_temporary_directory();
+
+    const fs::path& base_temporary_directory() noexcept { return BASE_TEMPORARY_DIRECTORY; }
 
 #if FILESYSTEM_SYMLINK == FILESYSTEM_SYMLINK_NONE
     constexpr char no_filesystem_message[] =
@@ -132,7 +136,7 @@ namespace vcpkg::Test
     void create_symlink(const fs::path& target, const fs::path& file, std::error_code& ec)
     {
 #if FILESYSTEM_SYMLINK == FILESYSTEM_SYMLINK_STD
-        if (SYMLINKS_ALLOWED)
+        if (can_create_symlinks())
         {
             std::filesystem::path targetp = target.native();
             std::filesystem::path filep = file.native();
@@ -156,12 +160,12 @@ namespace vcpkg::Test
     void create_directory_symlink(const fs::path& target, const fs::path& file, std::error_code& ec)
     {
 #if FILESYSTEM_SYMLINK == FILESYSTEM_SYMLINK_STD
-        if (SYMLINKS_ALLOWED)
+        if (can_create_symlinks())
         {
             std::filesystem::path targetp = target.native();
             std::filesystem::path filep = file.native();
 
-            std::filesystem::create_symlink(targetp, filep);
+            std::filesystem::create_directory_symlink(targetp, filep);
         }
         else
         {