From 627618a38d291d9cc76c8e30e33cad60dc26cf11 Mon Sep 17 00:00:00 2001
From: daurnimator <quae@daurnimator.com>
Date: Wed, 15 Jan 2020 18:11:54 +1000
Subject: [PATCH] std: add Dir.changeDir as wrapper around fchdir

---
 lib/std/c.zig        |  1 +
 lib/std/fs.zig       |  4 ++++
 lib/std/os.zig       | 14 ++++++++++++++
 lib/std/os/linux.zig |  4 ++++
 4 files changed, 23 insertions(+)

diff --git a/lib/std/c.zig b/lib/std/c.zig
index 79a6c07c0..84a9e92de 100644
--- a/lib/std/c.zig
+++ b/lib/std/c.zig
@@ -105,6 +105,7 @@ pub extern "c" fn mkdirat(dirfd: fd_t, path: [*:0]const u8, mode: u32) c_int;
 pub extern "c" fn symlink(existing: [*:0]const u8, new: [*:0]const u8) c_int;
 pub extern "c" fn rename(old: [*:0]const u8, new: [*:0]const u8) c_int;
 pub extern "c" fn chdir(path: [*:0]const u8) c_int;
+pub extern "c" fn fchdir(fd: fd_t) c_int;
 pub extern "c" fn execve(path: [*:0]const u8, argv: [*:null]const ?[*:0]const u8, envp: [*:null]const ?[*:0]const u8) c_int;
 pub extern "c" fn dup(fd: fd_t) c_int;
 pub extern "c" fn dup2(old_fd: fd_t, new_fd: fd_t) c_int;
diff --git a/lib/std/fs.zig b/lib/std/fs.zig
index f245ab348..f9c7071ab 100644
--- a/lib/std/fs.zig
+++ b/lib/std/fs.zig
@@ -890,6 +890,10 @@ pub const Dir = struct {
         try os.mkdiratC(self.fd, sub_path, default_new_dir_mode);
     }
 
+    pub fn changeTo(self: Dir) !void {
+        try os.fchdir(self.fd);
+    }
+
     /// Deprecated; call `openDirList` directly.
     pub fn openDir(self: Dir, sub_path: []const u8) OpenError!Dir {
         return self.openDirList(sub_path);
diff --git a/lib/std/os.zig b/lib/std/os.zig
index f97676a82..7563a34f2 100644
--- a/lib/std/os.zig
+++ b/lib/std/os.zig
@@ -1706,6 +1706,20 @@ pub fn chdirC(dir_path: [*:0]const u8) ChangeCurDirError!void {
     }
 }
 
+pub fn fchdir(dirfd: fd_t) ChangeCurDirError!void {
+    while (true) {
+        switch (errno(system.fchdir(dirfd))) {
+            0 => return,
+            EACCES => return error.AccessDenied,
+            EBADF => unreachable,
+            ENOTDIR => return error.NotDir,
+            EINTR => continue,
+            EIO => return error.FileSystem,
+            else => |err| return unexpectedErrno(err),
+        }
+    }
+}
+
 pub const ReadLinkError = error{
     AccessDenied,
     FileSystem,
diff --git a/lib/std/os/linux.zig b/lib/std/os/linux.zig
index de2ff5871..719e54184 100644
--- a/lib/std/os/linux.zig
+++ b/lib/std/os/linux.zig
@@ -76,6 +76,10 @@ pub fn chdir(path: [*:0]const u8) usize {
     return syscall1(SYS_chdir, @ptrToInt(path));
 }
 
+pub fn fchdir(fd: fd_t) usize {
+    return syscall1(SYS_fchdir, @bitCast(usize, @as(isize, fd)));
+}
+
 pub fn chroot(path: [*:0]const u8) usize {
     return syscall1(SYS_chroot, @ptrToInt(path));
 }