add indexed_set mod for typed wrappers around bitarrays representing sets.

It provides an `Idx` trait for usize wrappers used to represent the
elements of such sets.

src/librustc_borrowck/indexed_set.rs

@@ -0,0 +1,87 @@
+// Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::fmt;
+use std::marker::PhantomData;
+use std::mem;
+use bitslice::{BitSlice, Word};
+
+pub trait Indexed {
+    type Idx: Idx;
+}
+
+pub trait Idx {
+    fn idx(&self) -> usize;
+}
+
+pub struct OwnIdxSet<T: Idx> {
+    _pd: PhantomData<fn(&[T], usize) -> &T>,
+    bits: Vec<Word>,
+}
+
+// pnkfelix wants to have this be `IdxSet<T>([Word]) and then pass
+// around `&mut IdxSet<T>` or `&IdxSet<T>`.
+//
+// Mmapping a `&OwnIdxSet<T>` to `&IdxSet<T>` (at least today)
+// requires a transmute relying on representation guarantees that may
+// not hold in the future.
+
+pub struct IdxSet<T: Idx> {
+    _pd: PhantomData<fn(&[T], usize) -> &T>,
+    bits: [Word],
+}
+
+impl<T: Idx> fmt::Debug for OwnIdxSet<T> {
+    fn fmt(&self, w: &mut fmt::Formatter) -> fmt::Result { self.bits.fmt(w) }
+}
+
+impl<T: Idx> fmt::Debug for IdxSet<T> {
+    fn fmt(&self, w: &mut fmt::Formatter) -> fmt::Result { self.bits.fmt(w) }
+}
+
+impl<T: Idx> OwnIdxSet<T> {
+    fn new(init: Word, universe_size: usize) -> Self {
+        let bits_per_word = mem::size_of::<Word>();
+        let num_words = (universe_size + (bits_per_word - 1)) / bits_per_word;
+        OwnIdxSet {
+            _pd: Default::default(),
+            bits: vec![init; num_words],
+        }
+    }
+
+    /// Creates set holding every element whose index falls in range 0..universe_size.
+    pub fn new_filled(universe_size: usize) -> Self {
+        Self::new(!0, universe_size)
+    }
+
+    /// Creates set holding no elements.
+    pub fn new_empty(universe_size: usize) -> Self {
+        Self::new(0, universe_size)
+    }
+
+    /// Removes `elem` from the set `self`; returns true iff this changed `self`.
+    pub fn clear(&mut self, elem: &T) -> bool {
+        self.bits.clear_bit(elem.idx())
+    }
+
+    /// Adds `elem` to the set `self`; returns true iff this changed `self`.
+    pub fn add(&mut self, elem: &T) -> bool {
+        self.bits.set_bit(elem.idx())
+    }
+
+    /// Returns true iff set `self` contains `elem`.
+    pub fn contains(&self, elem: &T) -> bool {
+        self.bits.get_bit(elem.idx())
+    }
+
+    pub fn bits(&self) -> &[Word] {
+        &self.bits[..]
+    }
+}

src/librustc_borrowck/lib.rs

@@ -47,6 +47,7 @@ pub mod diagnostics;
 
 mod borrowck;
 mod bitslice;
+mod indexed_set;
 
 pub mod graphviz;