Auto merge of #34077 - durka:patch-23, r=alexcrichton

upgrade thread_local! invocation syntax

Allows declaring multiple statics in one macro invocation, and supports attaching attributes to the generated items. In particular, `#![forbid(missing_docs, unused)]` is now tenable on a crate/module containing thread locals.

For an example see [here](https://is.gd/aVFZZF). This change is fully backwards compatible as far as I can tell.

cc @frankmcsherry

1 files changed, 38 insertions, 4 deletions

diff --git a/src/libstd/thread/local.rs b/src/libstd/thread/local.rs
index 6b54ec8afca..152b9771086 100644
--- a/src/libstd/thread/local.rs
+++ b/src/libstd/thread/local.rs
@@ -100,18 +100,52 @@ pub struct LocalKey<T: 'static> {
 
 /// Declare a new thread local storage key of type `std::thread::LocalKey`.
 ///
+/// # Syntax
+///
+/// The macro wraps any number of static declarations and makes them thread local.
+/// Each static may be public or private, and attributes are allowed. Example:
+///
+/// ```
+/// use std::cell::RefCell;
+/// thread_local! {
+///     pub static FOO: RefCell<u32> = RefCell::new(1);
+///
+///     #[allow(unused)]
+///     static BAR: RefCell<f32> = RefCell::new(1.0);
+/// }
+/// # fn main() {}
+/// ```
+///
 /// See [LocalKey documentation](thread/struct.LocalKey.html) for more
 /// information.
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[allow_internal_unstable]
 macro_rules! thread_local {
-    (static $name:ident: $t:ty = $init:expr) => (
-        static $name: $crate::thread::LocalKey<$t> =
+    // rule 0: empty (base case for the recursion)
+    () => {};
+
+    // rule 1: process multiple declarations where the first one is private
+    ($(#[$attr:meta])* static $name:ident: $t:ty = $init:expr; $($rest:tt)*) => (
+        thread_local!($(#[$attr])* static $name: $t = $init); // go to rule 2
+        thread_local!($($rest)*);
+    );
+
+    // rule 2: handle a single private declaration
+    ($(#[$attr:meta])* static $name:ident: $t:ty = $init:expr) => (
+        $(#[$attr])* static $name: $crate::thread::LocalKey<$t> =
             __thread_local_inner!($t, $init);
     );
-    (pub static $name:ident: $t:ty = $init:expr) => (
-        pub static $name: $crate::thread::LocalKey<$t> =
+
+    // rule 3: handle multiple declarations where the first one is public
+    ($(#[$attr:meta])* pub static $name:ident: $t:ty = $init:expr; $($rest:tt)*) => (
+        thread_local!($(#[$attr])* pub static $name: $t = $init); // go to rule 4
+        thread_local!($($rest)*);
+    );
+
+    // rule 4: handle a single public declaration
+    ($(#[$attr:meta])* pub static $name:ident: $t:ty = $init:expr) => (
+        $(#[$attr])* pub static $name: $crate::thread::LocalKey<$t> =
             __thread_local_inner!($t, $init);
     );
 }