fs: seal OpenOptionsExt and DirBuilderExt (#2909)

tokio/src/fs/os/unix/dir_builder_ext.rs

@@ -3,7 +3,7 @@ use crate::fs::dir_builder::DirBuilder;
 /// Unix-specific extensions to [`DirBuilder`].
 ///
 /// [`DirBuilder`]: crate::fs::DirBuilder
-pub trait DirBuilderExt {
+pub trait DirBuilderExt: sealed::Sealed {
     /// Sets the mode to create new directories with.
     ///
     /// This option defaults to 0o777.
@@ -27,3 +27,10 @@ impl DirBuilderExt for DirBuilder {
         self
     }
 }
+
+impl sealed::Sealed for DirBuilder {}
+
+pub(crate) mod sealed {
+    #[doc(hidden)]
+    pub trait Sealed {}
+}

tokio/src/fs/os/unix/open_options_ext.rs

@@ -8,7 +8,7 @@ use std::os::unix::fs::OpenOptionsExt as StdOpenOptionsExt;
 ///
 /// [`fs::OpenOptions`]: crate::fs::OpenOptions
 /// [`std::os::unix::fs::OpenOptionsExt`]: std::os::unix::fs::OpenOptionsExt
-pub trait OpenOptionsExt {
+pub trait OpenOptionsExt: sealed::Sealed {
     /// Sets the mode bits that a new file will be created with.
     ///
     /// If a new file is created as part of an `OpenOptions::open` call then this
@@ -77,3 +77,10 @@ impl OpenOptionsExt for OpenOptions {
         self
     }
 }
+
+impl sealed::Sealed for OpenOptions {}
+
+pub(crate) mod sealed {
+    #[doc(hidden)]
+    pub trait Sealed {}
+}