Upgrade rust/crates/futures-executor to 0.3.12

Test: make
Change-Id: I12d01f1fee572bd237ca5f26f369e7ae2e65ddc6

src/lib.rs

diff --git a/src/lib.rs b/src/lib.rs
index a8ba5c8..b679649 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,7 +1,40 @@
 //! Built-in executors and related tools.
 //!
-//! All items of this library are only available when the `std` feature of this
+//! All asynchronous computation occurs within an executor, which is
+//! capable of spawning futures as tasks. This module provides several
+//! built-in executors, as well as tools for building your own.
+//!
+//! All items are only available when the `std` feature of this
 //! library is activated, and it is activated by default.
+//!
+//! # Using a thread pool (M:N task scheduling)
+//!
+//! Most of the time tasks should be executed on a [thread pool](ThreadPool).
+//! A small set of worker threads can handle a very large set of spawned tasks
+//! (which are much lighter weight than threads). Tasks spawned onto the pool
+//! with the [`spawn_ok`](ThreadPool::spawn_ok) function will run ambiently on
+//! the created threads.
+//!
+//! # Spawning additional tasks
+//!
+//! Tasks can be spawned onto a spawner by calling its [`spawn_obj`] method
+//! directly. In the case of `!Send` futures, [`spawn_local_obj`] can be used
+//! instead.
+//!
+//! # Single-threaded execution
+//!
+//! In addition to thread pools, it's possible to run a task (and the tasks
+//! it spawns) entirely within a single thread via the [`LocalPool`] executor.
+//! Aside from cutting down on synchronization costs, this executor also makes
+//! it possible to spawn non-`Send` tasks, via [`spawn_local_obj`]. The
+//! [`LocalPool`] is best suited for running I/O-bound tasks that do relatively
+//! little work between I/O operations.
+//!
+//! There is also a convenience function [`block_on`] for simply running a
+//! future to completion on the current thread.
+//!
+//! [`spawn_obj`]: https://docs.rs/futures/0.3/futures/task/trait.Spawn.html#tymethod.spawn_obj
+//! [`spawn_local_obj`]: https://docs.rs/futures/0.3/futures/task/trait.LocalSpawn.html#tymethod.spawn_local_obj
 
 #![cfg_attr(not(feature = "std"), no_std)]
 
@@ -9,16 +42,8 @@
 // It cannot be included in the published code because this lints have false positives in the minimum required version.
 #![cfg_attr(test, warn(single_use_lifetimes))]
 #![warn(clippy::all)]
-
-// mem::take requires Rust 1.40, matches! requires Rust 1.42
-// Can be removed if the minimum supported version increased or if https://github.com/rust-lang/rust-clippy/issues/3941
-// get's implemented.
-#![allow(clippy::mem_replace_with_default, clippy::match_like_matches_macro)]
-
 #![doc(test(attr(deny(warnings), allow(dead_code, unused_assignments, unused_variables))))]
 
-#![doc(html_root_url = "https://docs.rs/futures-executor/0.3.7")]
-
 #![cfg_attr(docsrs, feature(doc_cfg))]
 
 #[cfg(feature = "std")]

src/local_pool.rs

diff --git a/src/local_pool.rs b/src/local_pool.rs
index b089a80..156d5cc 100644
--- a/src/local_pool.rs
+++ b/src/local_pool.rs
@@ -118,8 +118,8 @@
 
 impl LocalPool {
     /// Create a new, empty pool of tasks.
-    pub fn new() -> LocalPool {
-        LocalPool {
+    pub fn new() -> Self {
+        Self {
             pool: FuturesUnordered::new(),
             incoming: Default::default(),
         }

src/thread_pool.rs

diff --git a/src/thread_pool.rs b/src/thread_pool.rs
index 3247aa3..741e6d9 100644
--- a/src/thread_pool.rs
+++ b/src/thread_pool.rs
@@ -80,7 +80,7 @@
     /// See documentation for the methods in
     /// [`ThreadPoolBuilder`](ThreadPoolBuilder) for details on the default
     /// configuration.
-    pub fn new() -> Result<ThreadPool, io::Error> {
+    pub fn new() -> Result<Self, io::Error> {
         ThreadPoolBuilder::new().create()
     }
 
@@ -168,9 +168,9 @@
 }
 
 impl Clone for ThreadPool {
-    fn clone(&self) -> ThreadPool {
+    fn clone(&self) -> Self {
         self.state.cnt.fetch_add(1, Ordering::Relaxed);
-        ThreadPool { state: self.state.clone() }
+        Self { state: self.state.clone() }
     }
 }
 
@@ -313,7 +313,7 @@
     /// Actually run the task (invoking `poll` on the future) on the current
     /// thread.
     fn run(self) {
-        let Task { mut future, wake_handle, mut exec } = self;
+        let Self { mut future, wake_handle, mut exec } = self;
         let waker = waker_ref(&wake_handle);
         let mut cx = Context::from_waker(&waker);
 
@@ -328,7 +328,7 @@
                     Poll::Pending => {}
                     Poll::Ready(()) => return wake_handle.mutex.complete(),
                 }
-                let task = Task {
+                let task = Self {
                     future,
                     wake_handle: wake_handle.clone(),
                     exec,

src/unpark_mutex.rs

diff --git a/src/unpark_mutex.rs b/src/unpark_mutex.rs
index 1f69aed..c49c64c 100644
--- a/src/unpark_mutex.rs
+++ b/src/unpark_mutex.rs
@@ -43,8 +43,8 @@
 const COMPLETE: usize = 3;      // No transitions out
 
 impl<D> UnparkMutex<D> {
-    pub(crate) fn new() -> UnparkMutex<D> {
-        UnparkMutex {
+    pub(crate) fn new() -> Self {
+        Self {
             status: AtomicUsize::new(WAITING),
             inner: UnsafeCell::new(None),
         }