Utilize PhantomData to enforce !Sync and !Send field.

[frewsxcv]

No description provided.

[nagisa]

cc @alexcrichton, a nice optimisation. Some backward compat hazard if anybody does transmute out of these, but I don’t think that would ever be problematic.

[alexcrichton]

@bors: r+ 404e31b4e7f07031843bdfdba4d09e0b18eb1085

Looks good to me, thanks!

[bors]

⌛ Testing commit 404e31b with merge 78cdb1e...

[bors]

💔 Test failed - auto-linux-64-cross-freebsd

[frewsxcv]

Compile errors fixed in the latest force push.

diff --git a/src/libstd/sys/unix/os.rs b/src/libstd/sys/unix/os.rs
index bc4c22a..6b8dfa5 100644
--- a/src/libstd/sys/unix/os.rs
+++ b/src/libstd/sys/unix/os.rs
@@ -400,7 +400,7 @@ pub fn args() -> Args {
         }
     }

-    Args { iter: res.into_iter(), _dont_send_or_sync_me: ptr::null_mut() }
+    Args { iter: res.into_iter(), _dont_send_or_sync_me: PhantomData }
 }

 #[cfg(any(target_os = "linux",
@@ -419,7 +419,7 @@ pub fn args() -> Args {
     let v: Vec<OsString> = bytes.into_iter().map(|v| {
         OsStringExt::from_vec(v)
     }).collect();
-    Args { iter: v.into_iter(), _dont_send_or_sync_me: ptr::null_mut() }
+    Args { iter: v.into_iter(), _dont_send_or_sync_me: PhantomData }
 }

 pub struct Env {

[alexcrichton]

@bors: r+ 28218be

[bors]

⌛ Testing commit 28218be with merge f013914...

[apasel422]

Out of curiosity, is there a reason that the following doesn't work?

struct Args {
    iter: vec::IntoIter<OsString>,
}

struct Env {
    iter: vec::IntoIter<(OsString, OsString)>,
}

impl !Send for Args {}
impl !Sync for Args {}

impl !Send for Env {}
impl !Sync for Env {}

It ends up giving a better error message when you try to use these types in a Send or Sync context because it doesn't mention the types' internal fields.

[alexcrichton]

@apasel422 yeah I think that'd work but impl !Foo is unstable right now and I just personally tend to lean towards stable before unstable things.

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-cargotest, auto-linux-64-cross-freebsd, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-opt-no-mir, auto-linux-64-opt-rustbuild, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-opt, auto-mac-64-opt-rustbuild, auto-mac-cross-ios-opt, auto-win-gnu-32-opt, auto-win-gnu-32-opt-rustbuild, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-cargotest, auto-win-msvc-64-opt, auto-win-msvc-64-opt-no-mir, auto-win-msvc-64-opt-rustbuild
Approved by: alexcrichton
Pushing f013914 to master...