std: Add a new top-level thread_local module

This commit removes the `std::local_data` module in favor of a new
`std::thread_local` module providing thread local storage. The module provides
two variants of TLS: one which owns its contents and one which is based on
scoped references. Each implementation has pros and cons listed in the
documentation.

Both flavors have accessors through a function called `with` which yield a
reference to a closure provided. Both flavors also panic if a reference cannot
be yielded and provide a function to test whether an access would panic or not.
This is an implementation of [RFC 461][rfc] and full details can be found in
that RFC.

This is a breaking change due to the removal of the `std::local_data` module.
All users can migrate to the new thread local system like so:

    thread_local!(static FOO: Rc<RefCell<Option<T>>> = Rc::new(RefCell::new(None)))

The old `local_data` module inherently contained the `Rc<RefCell<Option<T>>>` as
an implementation detail which must now be explicitly stated by users.

[rfc]: https://github.com/rust-lang/rfcs/pull/461
[breaking-change]

1 files changed, 12 insertions, 20 deletions

diff --git a/src/libsyntax/diagnostics/plugin.rs b/src/libsyntax/diagnostics/plugin.rs
index 281bde3129a..5f4e675aad5 100644
--- a/src/libsyntax/diagnostics/plugin.rs
+++ b/src/libsyntax/diagnostics/plugin.rs
@@ -18,31 +18,23 @@ use ext::build::AstBuilder;
 use parse::token;
 use ptr::P;
 
-local_data_key!(registered_diagnostics: RefCell<HashMap<Name, Option<Name>>>)
-local_data_key!(used_diagnostics: RefCell<HashMap<Name, Span>>)
+thread_local!(static REGISTERED_DIAGNOSTICS: RefCell<HashMap<Name, Option<Name>>> = {
+    RefCell::new(HashMap::new())
+})
+thread_local!(static USED_DIAGNOSTICS: RefCell<HashMap<Name, Span>> = {
+    RefCell::new(HashMap::new())
+})
 
 fn with_registered_diagnostics<T>(f: |&mut HashMap<Name, Option<Name>>| -> T) -> T {
-    match registered_diagnostics.get() {
-        Some(cell) => f(cell.borrow_mut().deref_mut()),
-        None => {
-            let mut map = HashMap::new();
-            let value = f(&mut map);
-            registered_diagnostics.replace(Some(RefCell::new(map)));
-            value
-        }
-    }
+    REGISTERED_DIAGNOSTICS.with(|slot| {
+        f(&mut *slot.borrow_mut())
+    })
 }
 
 fn with_used_diagnostics<T>(f: |&mut HashMap<Name, Span>| -> T) -> T {
-    match used_diagnostics.get() {
-        Some(cell) => f(cell.borrow_mut().deref_mut()),
-        None => {
-            let mut map = HashMap::new();
-            let value = f(&mut map);
-            used_diagnostics.replace(Some(RefCell::new(map)));
-            value
-        }
-    }
+    USED_DIAGNOSTICS.with(|slot| {
+        f(&mut *slot.borrow_mut())
+    })
 }
 
 pub fn expand_diagnostic_used<'cx>(ecx: &'cx mut ExtCtxt,