std: add chdir smoke test

lib/std/os.zig

@@ -2312,11 +2312,7 @@ pub fn chdir(dir_path: []const u8) ChangeCurDirError!void {
         var utf16_dir_path: [windows.PATH_MAX_WIDE]u16 = undefined;
         const len = try std.unicode.utf8ToUtf16Le(utf16_dir_path[0..], dir_path);
         if (len > utf16_dir_path.len) return error.NameTooLong;
-        
+        return chdirW(utf16_dir_path[0..len]);
-        windows.SetCurrentDirectory(utf16_dir_path[0..len]) catch |err| switch (err) {
-            error.NoDevice => return error.FileSystem,
-            else => |e| return e,
-        };
     } else {
         const dir_path_c = try toPosixPath(dir_path);
         return chdirZ(&dir_path_c);
@@ -2328,7 +2324,10 @@ pub const chdirC = @compileError("deprecated: renamed to chdirZ");
 /// Same as `chdir` except the parameter is null-terminated.
 pub fn chdirZ(dir_path: [*:0]const u8) ChangeCurDirError!void {
     if (builtin.os.tag == .windows) {
-        return chdir(mem.spanZ(dir_path));
+        var utf16_dir_path: [windows.PATH_MAX_WIDE]u16 = undefined;
+        const len = try std.unicode.utf8ToUtf16Le(utf16_dir_path[0..], dir_path);
+        if (len > utf16_dir_path.len) return error.NameTooLong;
+        return chdirW(utf16_dir_path[0..len]);
     }
     switch (errno(system.chdir(dir_path))) {
         0 => return,
@@ -2344,6 +2343,14 @@ pub fn chdirZ(dir_path: [*:0]const u8) ChangeCurDirError!void {
     }
 }
 
+/// Windows-only. Same as `chdir` except the paramter is WTF16 encoded.
+pub fn chdirW(dir_path: []const u16) ChangeCurDirError!void {
+    windows.SetCurrentDirectory(dir_path) catch |err| switch (err) {
+        error.NoDevice => return error.FileSystem,
+        else => |e| return e,
+    };
+}
+
 pub const FchdirError = error{
     AccessDenied,
     NotDir,

lib/std/os/test.zig

@@ -25,6 +25,30 @@ const tmpDir = std.testing.tmpDir;
 const Dir = std.fs.Dir;
 const ArenaAllocator = std.heap.ArenaAllocator;
 
+test "chdir smoke test" {
+    if (builtin.os.tag == .wasi) return error.SkipZigTest;
+
+    // Get current working directory path
+    var old_cwd_buf: [fs.MAX_PATH_BYTES]u8 = undefined;
+    const old_cwd = try os.getcwd(old_cwd_buf[0..]);
+
+    {
+        // Firstly, changing to itself should have no effect
+        try os.chdir(old_cwd);
+        var new_cwd_buf: [fs.MAX_PATH_BYTES]u8 = undefined;
+        const new_cwd = try os.getcwd(new_cwd_buf[0..]);
+        expect(mem.eql(u8, old_cwd, new_cwd));
+    }
+    {
+        // Next, change current working directory to one level above
+        const parent = fs.path.dirname(old_cwd) orelse unreachable; // old_cwd should be absolute
+        try os.chdir(parent);
+        var new_cwd_buf: [fs.MAX_PATH_BYTES]u8 = undefined;
+        const new_cwd = try os.getcwd(new_cwd_buf[0..]);
+        expect(mem.eql(u8, parent, new_cwd));
+    }
+}
+
 test "open smoke test" {
     if (builtin.os.tag == .wasi) return error.SkipZigTest;