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, 7 insertions, 21 deletions

diff --git a/src/libsyntax/ext/mtwt.rs b/src/libsyntax/ext/mtwt.rs
index 2ddcab10cda..e6d886e28ba 100644
--- a/src/libsyntax/ext/mtwt.rs
+++ b/src/libsyntax/ext/mtwt.rs
@@ -20,7 +20,6 @@ pub use self::SyntaxContext_::*;
 use ast::{Ident, Mrk, Name, SyntaxContext};
 
 use std::cell::RefCell;
-use std::rc::Rc;
 use std::collections::HashMap;
 use std::collections::hash_map::{Occupied, Vacant};
 
@@ -105,16 +104,8 @@ pub fn apply_renames(renames: &RenameList, ctxt: SyntaxContext) -> SyntaxContext
 
 /// Fetch the SCTable from TLS, create one if it doesn't yet exist.
 pub fn with_sctable<T>(op: |&SCTable| -> T) -> T {
-    local_data_key!(sctable_key: Rc<SCTable>)
-
-    match sctable_key.get() {
-        Some(ts) => op(&**ts),
-        None => {
-            let ts = Rc::new(new_sctable_internal());
-            sctable_key.replace(Some(ts.clone()));
-            op(&*ts)
-        }
-    }
+    thread_local!(static SCTABLE_KEY: SCTable = new_sctable_internal())
+    SCTABLE_KEY.with(|slot| op(slot))
 }
 
 // Make a fresh syntax context table with EmptyCtxt in slot zero
@@ -165,16 +156,11 @@ type ResolveTable = HashMap<(Name,SyntaxContext),Name>;
 // okay, I admit, putting this in TLS is not so nice:
 // fetch the SCTable from TLS, create one if it doesn't yet exist.
 fn with_resolve_table_mut<T>(op: |&mut ResolveTable| -> T) -> T {
-    local_data_key!(resolve_table_key: Rc<RefCell<ResolveTable>>)
-
-    match resolve_table_key.get() {
-        Some(ts) => op(&mut *ts.borrow_mut()),
-        None => {
-            let ts = Rc::new(RefCell::new(HashMap::new()));
-            resolve_table_key.replace(Some(ts.clone()));
-            op(&mut *ts.borrow_mut())
-        }
-    }
+    thread_local!(static RESOLVE_TABLE_KEY: RefCell<ResolveTable> = {
+        RefCell::new(HashMap::new())
+    })
+
+    RESOLVE_TABLE_KEY.with(|slot| op(&mut *slot.borrow_mut()))
 }
 
 /// Resolve a syntax object to a name, per MTWT.