Rollup merge of rust-lang#138822 - moxian:unlock, r=joshtriplett

De-Stabilize `file_lock`

This reverts rust-lang#136794

FCP on the tracking issue (rust-lang#130994) passsed successfully rust-lang#130994 (comment) but there are now concerns about the suitability of the proposed API (rust-lang#130994 (comment))

On zullip it was [suggested](https://rust-lang.zulipchat.com/#narrow/channel/219381-t-libs/topic/File.3A.3Atry_lock.20API.3A.20Result.3Cbool.3E/near/506823067) that it would be better to temporarily(?) destabilize the feature ASAP to buy us some more time reflecting on the API.

This PR implements the revert.

The feature is not currently on beta (https://github.com/rust-lang/rust/blob/beta/library/std/src/fs.rs#L672) so a beta backport is not yet neccessary.

If this revert is accepted, the tracking issue (rust-lang#130994) should be reopened

Author: matthiaskrgr

library/std/src/fs.rs

@@ -665,6 +665,7 @@ impl File {
     /// # Examples
     ///
     /// ```no_run
+    /// #![feature(file_lock)]
     /// use std::fs::File;
     ///
     /// fn main() -> std::io::Result<()> {
@@ -673,7 +674,7 @@ impl File {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "file_lock", since = "CURRENT_RUSTC_VERSION")]
+    #[unstable(feature = "file_lock", issue = "130994")]
     pub fn lock(&self) -> io::Result<()> {
         self.inner.lock()
     }
@@ -717,6 +718,7 @@ impl File {
     /// # Examples
     ///
     /// ```no_run
+    /// #![feature(file_lock)]
     /// use std::fs::File;
     ///
     /// fn main() -> std::io::Result<()> {
@@ -725,7 +727,7 @@ impl File {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "file_lock", since = "CURRENT_RUSTC_VERSION")]
+    #[unstable(feature = "file_lock", issue = "130994")]
     pub fn lock_shared(&self) -> io::Result<()> {
         self.inner.lock_shared()
     }
@@ -774,6 +776,7 @@ impl File {
     /// # Examples
     ///
     /// ```no_run
+    /// #![feature(file_lock)]
     /// use std::fs::File;
     ///
     /// fn main() -> std::io::Result<()> {
@@ -782,7 +785,7 @@ impl File {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "file_lock", since = "CURRENT_RUSTC_VERSION")]
+    #[unstable(feature = "file_lock", issue = "130994")]
     pub fn try_lock(&self) -> io::Result<bool> {
         self.inner.try_lock()
     }
@@ -830,6 +833,7 @@ impl File {
     /// # Examples
     ///
     /// ```no_run
+    /// #![feature(file_lock)]
     /// use std::fs::File;
     ///
     /// fn main() -> std::io::Result<()> {
@@ -838,7 +842,7 @@ impl File {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "file_lock", since = "CURRENT_RUSTC_VERSION")]
+    #[unstable(feature = "file_lock", issue = "130994")]
     pub fn try_lock_shared(&self) -> io::Result<bool> {
         self.inner.try_lock_shared()
     }
@@ -866,6 +870,7 @@ impl File {
     /// # Examples
     ///
     /// ```no_run
+    /// #![feature(file_lock)]
     /// use std::fs::File;
     ///
     /// fn main() -> std::io::Result<()> {
@@ -875,7 +880,7 @@ impl File {
     ///     Ok(())
     /// }
     /// ```
-    #[stable(feature = "file_lock", since = "CURRENT_RUSTC_VERSION")]
+    #[unstable(feature = "file_lock", issue = "130994")]
     pub fn unlock(&self) -> io::Result<()> {
         self.inner.unlock()
     }