Commit 83abd73801a6ab3125c1b0b8ba432be188c9e7ca | zig

author	Tom Read Cutting <readcuttingt@gmail.com> 2025-12-03 07:06:16+00:00
committer	Ryan Liptak <squeek502@hotmail.com> 2026-02-02 01:21:11-08:00
log	83abd73801a6ab3125c1b0b8ba432be188c9e7ca
tree	3dae948af47e654a894de3881f8d3df9aa1d1be3
parent	aacf8ce03d2b52e52830873c40eabb1cb1eb8272

Windows: Support directory handle for cwd instead of string for Child.process

This implementation is a bit of a hacky workaround, as we use a ntdll
API to grab the full path of the directory handle. As far as I can tell
this might be the only solution to the problem, as
kernel32.CreateProcessW takes a directory path as a string only.

I might be wrong though as haven't researched the problem thoroughly.

2 files changed, 25 insertions(+), 6 deletions(-)

lib
- std
  - Io
    Threaded.zig
  - process.zig

lib/std/Io/Threaded.zig+22-6

 @@ -15193,7 +15193,26 @@ fn processSpawnWindows(userdata: ?*anyopaque, options: process.SpawnOptions) pro
     defer arena_allocator.deinit();
     const arena = arena_allocator.allocator();
-    const cwd_w = if (options.cwd) |cwd| try std.unicode.wtf8ToWtf16LeAllocZ(arena, cwd) else null;
+    const cwd_w = cwd_w: {
+        if (options.cwd_dir) |cwd_dir| {
+            var dir_path_buffer = try arena.alloc(u16, windows.PATH_MAX_WIDE + 1);
+            // TODO move GetFinalPathNameByHandle logic into std.Io.Threaded and add cancel checks
+            try Thread.checkCancel();
+            const dir_path = try windows.GetFinalPathNameByHandle(
+                cwd_dir.handle,
+                .{},
+                dir_path_buffer[0..windows.PATH_MAX_WIDE],
+            );
+            dir_path_buffer[dir_path.len] = 0;
+            // Shrink the allocation down to just the path buffer + sentinel
+            dir_path_buffer = try arena.realloc(dir_path_buffer, dir_path.len + 1);
+            break :cwd_w dir_path_buffer[0..dir_path.len :0];
+        } else if (options.cwd) |cwd| {
+            break :cwd_w try std.unicode.wtf8ToWtf16LeAllocZ(arena, cwd);
+        } else {
+            break :cwd_w null;
+        }
+    };
     const cwd_w_ptr = if (cwd_w) |cwd| cwd.ptr else null;
     const maybe_envp_buf = if (options.environ_map) |environ_map| try environ_map.createBlockWindows(arena) else null;
 @@ -15204,16 +15223,13 @@ fn processSpawnWindows(userdata: ?*anyopaque, options: process.SpawnOptions) pro
     // The cwd provided by options is in effect when choosing the executable
     // path to match POSIX semantics.
-    var cwd_path_w_needs_free = false;
     const cwd_path_w = x: {
         // If the app name is absolute, then we need to use its dirname as the cwd
         if (app_name_is_absolute) {
-            cwd_path_w_needs_free = true;
             const dir = Dir.path.dirname(app_name_wtf8).?;
             break :x try std.unicode.wtf8ToWtf16LeAllocZ(arena, dir);
-        } else if (options.cwd) |cwd| {
+        } else if (cwd_w) |cwd| {
-            cwd_path_w_needs_free = true;
+            break :x cwd;
-            break :x try std.unicode.wtf8ToWtf16LeAllocZ(arena, cwd);
         } else {
             break :x &[_:0]u16{}; // empty for cwd
         }

lib/std/process.zig+3

 @@ -359,6 +359,9 @@ pub const SpawnError = error{
     /// children of the calling process and the child had already performed an
     /// image replacement.
     ProcessAlreadyExec,
+    /// On Windows, the volume does not contain a recognized file system. File
+    /// system drivers might not be loaded, or the volume may be corrupt.
+    UnrecognizedVolume,
 } || Io.Dir.PathNameError || Io.Cancelable || Io.UnexpectedError;
 pub const SpawnOptions = struct {