Fix long cache file path on Windows (#3065)

.gitignore

@@ -3,16 +3,12 @@ __pycache__/
 *.py[cod]
 *$py.class
 
-# C extensions
-*.so
-
 # tensor files
 *.safe
 *.safetensors
 
 # Metal libraries
 *.metallib
-venv/
 
 # Distribution / packaging
 python/mlx/core
@@ -30,6 +26,7 @@ lib64/
 parts/
 sdist/
 var/
+venv/
 wheels/
 share/python-wheels/
 *.egg-info/
@@ -37,12 +34,7 @@ share/python-wheels/
 *.egg
 MANIFEST
 uv.lock
-
-# vim
-*.swp
-
-# Ignore build dir
-build/
+.DS_Store
 
 # Prerequisites
 *.d
@@ -52,6 +44,7 @@ build/
 *.lo
 *.o
 *.obj
+*.ilk
 
 # Precompiled Headers
 *.gch
@@ -80,9 +73,9 @@ build/
 # Debug symbols
 *.pdb
 
-# VSCode 
+# VSCode
 .vscode/
-.DS_Store
-
 # Jetbrains
-.cache
+.cache/
+# vim
+*.swp

mlx/backend/cuda/jit_module.cpp

@@ -79,6 +79,18 @@ const std::filesystem::path& ptx_cache_dir() {
       cache =
           std::filesystem::temp_directory_path() / "mlx" / version() / "ptx";
     }
+
+#if defined(_WIN32)
+    // Add "\\?\" prefix to support long file path.
+    const wchar_t* long_path_prefix = L"\\\\?\\";
+    if (cache.is_relative()) {
+      cache = std::filesystem::absolute(cache);
+    }
+    if (!cache.native().starts_with(long_path_prefix)) {
+      cache = long_path_prefix + cache.native();
+    }
+#endif
+
     if (!std::filesystem::exists(cache)) {
       std::error_code error;
       if (!std::filesystem::create_directories(cache, error)) {
@@ -93,12 +105,7 @@ const std::filesystem::path& ptx_cache_dir() {
 std::filesystem::path get_ptx_path(
     const std::filesystem::path& cache_dir,
     const std::string& module_name) {
-#ifdef _WIN32
-  constexpr int max_file_name_length = 140;
-#else
   constexpr int max_file_name_length = 245;
-#endif
-
   if (module_name.size() <= max_file_name_length) {
     return cache_dir / (module_name + ".ptx");
   }