Rollup merge of rust-lang#37551 - Mark-Simulacrum:upgrade-accvec, r=e…

…ddyb

Replace syntax's SmallVector with AccumulateVec

This adds a new type to data_structures, `SmallVec`, which wraps `AccumulateVec` with support for re-allocating onto the heap (`SmallVec::reserve`). `SmallVec` is then used to replace the implementation of `SmallVector` in libsyntax.

r? @eddyb

Fixes rust-lang#37371. Using `SmallVec` instead of libsyntax's `SmallVector` will provide the `N = 2/4` case easily (just needs a few more `Array` impls).

cc @nnethercote, probably interested in this area

mk/crates.mk

@@ -100,7 +100,7 @@ DEPS_serialize := std log
 DEPS_term := std
 DEPS_test := std getopts term native:rust_test_helpers
 
-DEPS_syntax := std term serialize log arena libc rustc_bitflags rustc_unicode rustc_errors syntax_pos
+DEPS_syntax := std term serialize log arena libc rustc_bitflags rustc_unicode rustc_errors syntax_pos rustc_data_structures
 DEPS_syntax_ext := syntax syntax_pos rustc_errors fmt_macros proc_macro
 DEPS_syntax_pos := serialize
 DEPS_proc_macro_tokens := syntax syntax_pos log

src/librustc/infer/combine.rs

@@ -184,7 +184,7 @@ impl<'infcx, 'gcx, 'tcx> CombineFields<'infcx, 'gcx, 'tcx> {
     {
         // We use SmallVector here instead of Vec because this code is hot and
         // it's rare that the stack length exceeds 1.
-        let mut stack = SmallVector::zero();
+        let mut stack = SmallVector::new();
         stack.push((a_ty, dir, b_vid));
         loop {
             // For each turn of the loop, we extract a tuple

src/librustc_data_structures/accumulate_vec.rs

@@ -11,22 +11,68 @@
 //! A vector type intended to be used for collecting from iterators onto the stack.
 //!
 //! Space for up to N elements is provided on the stack.  If more elements are collected, Vec is
-//! used to store the values on the heap. This type does not support re-allocating onto the heap,
-//! and there is no way to push more elements onto the existing storage.
+//! used to store the values on the heap.
 //!
 //! The N above is determined by Array's implementor, by way of an associatated constant.
 
-use std::ops::Deref;
-use std::iter::{IntoIterator, FromIterator};
+use std::ops::{Deref, DerefMut};
+use std::iter::{self, IntoIterator, FromIterator};
+use std::slice;
+use std::vec;
 
-use array_vec::{Array, ArrayVec};
+use rustc_serialize::{Encodable, Encoder, Decodable, Decoder};
 
-#[derive(Debug)]
+use array_vec::{self, Array, ArrayVec};
+
+#[derive(PartialEq, Eq, Hash, Debug)]
 pub enum AccumulateVec<A: Array> {
     Array(ArrayVec<A>),
     Heap(Vec<A::Element>)
 }
 
+impl<A> Clone for AccumulateVec<A>
+    where A: Array,
+          A::Element: Clone {
+    fn clone(&self) -> Self {
+        match *self {
+            AccumulateVec::Array(ref arr) => AccumulateVec::Array(arr.clone()),
+            AccumulateVec::Heap(ref vec) => AccumulateVec::Heap(vec.clone()),
+        }
+    }
+}
+
+impl<A: Array> AccumulateVec<A> {
+    pub fn new() -> AccumulateVec<A> {
+        AccumulateVec::Array(ArrayVec::new())
+    }
+
+    pub fn one(el: A::Element) -> Self {
+        iter::once(el).collect()
+    }
+
+    pub fn many<I: IntoIterator<Item=A::Element>>(iter: I) -> Self {
+        iter.into_iter().collect()
+    }
+
+    pub fn len(&self) -> usize {
+        match *self {
+            AccumulateVec::Array(ref arr) => arr.len(),
+            AccumulateVec::Heap(ref vec) => vec.len(),
+        }
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    pub fn pop(&mut self) -> Option<A::Element> {
+        match *self {
+            AccumulateVec::Array(ref mut arr) => arr.pop(),
+            AccumulateVec::Heap(ref mut vec) => vec.pop(),
+        }
+    }
+}
+
 impl<A: Array> Deref for AccumulateVec<A> {
     type Target = [A::Element];
     fn deref(&self) -> &Self::Target {
@@ -37,6 +83,15 @@ impl<A: Array> Deref for AccumulateVec<A> {
     }
 }
 
+impl<A: Array> DerefMut for AccumulateVec<A> {
+    fn deref_mut(&mut self) -> &mut [A::Element] {
+        match *self {
+            AccumulateVec::Array(ref mut v) => &mut v[..],
+            AccumulateVec::Heap(ref mut v) => &mut v[..],
+        }
+    }
+}
+
 impl<A: Array> FromIterator<A::Element> for AccumulateVec<A> {
     fn from_iter<I>(iter: I) -> AccumulateVec<A> where I: IntoIterator<Item=A::Element> {
         let iter = iter.into_iter();
@@ -50,3 +105,94 @@ impl<A: Array> FromIterator<A::Element> for AccumulateVec<A> {
     }
 }
 
+pub struct IntoIter<A: Array> {
+    repr: IntoIterRepr<A>,
+}
+
+enum IntoIterRepr<A: Array> {
+    Array(array_vec::Iter<A>),
+    Heap(vec::IntoIter<A::Element>),
+}
+
+impl<A: Array> Iterator for IntoIter<A> {
+    type Item = A::Element;
+
+    fn next(&mut self) -> Option<A::Element> {
+        match self.repr {
+            IntoIterRepr::Array(ref mut arr) => arr.next(),
+            IntoIterRepr::Heap(ref mut iter) => iter.next(),
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        match self.repr {
+            IntoIterRepr::Array(ref iter) => iter.size_hint(),
+            IntoIterRepr::Heap(ref iter) => iter.size_hint(),
+        }
+    }
+}
+
+impl<A: Array> IntoIterator for AccumulateVec<A> {
+    type Item = A::Element;
+    type IntoIter = IntoIter<A>;
+    fn into_iter(self) -> Self::IntoIter {
+        IntoIter {
+            repr: match self {
+                AccumulateVec::Array(arr) => IntoIterRepr::Array(arr.into_iter()),
+                AccumulateVec::Heap(vec) => IntoIterRepr::Heap(vec.into_iter()),
+            }
+        }
+    }
+}
+
+impl<'a, A: Array> IntoIterator for &'a AccumulateVec<A> {
+    type Item = &'a A::Element;
+    type IntoIter = slice::Iter<'a, A::Element>;
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+impl<'a, A: Array> IntoIterator for &'a mut AccumulateVec<A> {
+    type Item = &'a mut A::Element;
+    type IntoIter = slice::IterMut<'a, A::Element>;
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter_mut()
+    }
+}
+
+impl<A: Array> From<Vec<A::Element>> for AccumulateVec<A> {
+    fn from(v: Vec<A::Element>) -> AccumulateVec<A> {
+        AccumulateVec::many(v)
+    }
+}
+
+impl<A: Array> Default for AccumulateVec<A> {
+    fn default() -> AccumulateVec<A> {
+        AccumulateVec::new()
+    }
+}
+
+impl<A> Encodable for AccumulateVec<A>
+    where A: Array,
+          A::Element: Encodable {
+    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+        s.emit_seq(self.len(), |s| {
+            for (i, e) in self.iter().enumerate() {
+                try!(s.emit_seq_elt(i, |s| e.encode(s)));
+            }
+            Ok(())
+        })
+    }
+}
+
+impl<A> Decodable for AccumulateVec<A>
+    where A: Array,
+          A::Element: Decodable {
+    fn decode<D: Decoder>(d: &mut D) -> Result<AccumulateVec<A>, D::Error> {
+        d.read_seq(|d, len| {
+            Ok(try!((0..len).map(|i| d.read_seq_elt(i, |d| Decodable::decode(d))).collect()))
+        })
+    }
+}
+