Use len instead of size_hint where appropiate

This makes it clearer that we're not just looking for a lower bound but
rather know that the iterator is an `ExactSizeIterator`.

src/libcollections/vec.rs

@@ -1658,7 +1658,7 @@ impl<T> Iterator for IntoIter<T> {
 
     #[inline]
     fn count(self) -> usize {
-        self.size_hint().0
+        self.len()
     }
 }
 

src/libcore/fmt/mod.rs

@@ -1384,7 +1384,7 @@ impl Debug for str {
         for (i, c) in self.char_indices() {
             let esc = c.escape_default();
             // If char needs escaping, flush backlog so far and write, else skip
-            if esc.size_hint() != (1, Some(1)) {
+            if esc.len() != 1 {
                 f.write_str(&self[from..i])?;
                 for c in esc {
                     f.write_char(c)?;

src/libcore/slice.rs

@@ -835,7 +835,7 @@ macro_rules! iterator {
 
             #[inline]
             fn count(self) -> usize {
-                self.size_hint().0
+                self.len()
             }
 
             #[inline]
@@ -1444,7 +1444,7 @@ impl<'a, T> Iterator for Windows<'a, T> {
 
     #[inline]
     fn count(self) -> usize {
-        self.size_hint().0
+        self.len()
     }
 
     #[inline]
@@ -1541,7 +1541,7 @@ impl<'a, T> Iterator for Chunks<'a, T> {
 
     #[inline]
     fn count(self) -> usize {
-        self.size_hint().0
+        self.len()
     }
 
     #[inline]
@@ -1632,7 +1632,7 @@ impl<'a, T> Iterator for ChunksMut<'a, T> {
 
     #[inline]
     fn count(self) -> usize {
-        self.size_hint().0
+        self.len()
     }
 
     #[inline]

src/libcore/str/mod.rs

@@ -433,7 +433,7 @@ impl<'a> Iterator for Chars<'a> {
 
     #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
-        let (len, _) = self.iter.size_hint();
+        let len = self.iter.len();
         // `(len + 3)` can't overflow, because we know that the `slice::Iter`
         // belongs to a slice in memory which has a maximum length of
         // `isize::MAX` (that's well below `usize::MAX`).
@@ -480,12 +480,12 @@ impl<'a> Iterator for CharIndices<'a> {
 
     #[inline]
     fn next(&mut self) -> Option<(usize, char)> {
-        let (pre_len, _) = self.iter.iter.size_hint();
+        let pre_len = self.iter.iter.len();
         match self.iter.next() {
             None => None,
             Some(ch) => {
                 let index = self.front_offset;
-                let (len, _) = self.iter.iter.size_hint();
+                let len = self.iter.iter.len();
                 self.front_offset += pre_len - len;
                 Some((index, ch))
             }
@@ -505,8 +505,7 @@ impl<'a> DoubleEndedIterator for CharIndices<'a> {
         match self.iter.next_back() {
             None => None,
             Some(ch) => {
-                let (len, _) = self.iter.iter.size_hint();
+                let index = self.front_offset + self.iter.iter.len();
-                let index = self.front_offset + len;
                 Some((index, ch))
             }
         }

src/libcore/str/pattern.rs

@@ -310,9 +310,9 @@ unsafe impl<'a, C: CharEq> Searcher<'a> for CharEqSearcher<'a, C> {
         let s = &mut self.char_indices;
         // Compare lengths of the internal byte slice iterator
         // to find length of current char
-        let (pre_len, _) = s.iter.iter.size_hint();
+        let pre_len = s.iter.iter.len();
         if let Some((i, c)) = s.next() {
-            let (len, _) = s.iter.iter.size_hint();
+            let len = s.iter.iter.len();
             let char_len = pre_len - len;
             if self.char_eq.matches(c) {
                 return SearchStep::Match(i, i + char_len);
@@ -330,9 +330,9 @@ unsafe impl<'a, C: CharEq> ReverseSearcher<'a> for CharEqSearcher<'a, C> {
         let s = &mut self.char_indices;
         // Compare lengths of the internal byte slice iterator
         // to find length of current char
-        let (pre_len, _) = s.iter.iter.size_hint();
+        let pre_len = s.iter.iter.len();
         if let Some((i, c)) = s.next_back() {
-            let (len, _) = s.iter.iter.size_hint();
+            let len = s.iter.iter.len();
             let char_len = pre_len - len;
             if self.char_eq.matches(c) {
                 return SearchStep::Match(i, i + char_len);

src/libstd/sys/common/wtf8.rs

@@ -715,7 +715,7 @@ impl<'a> Iterator for Wtf8CodePoints<'a> {
 
     #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
-        let (len, _) = self.bytes.size_hint();
+        let len = self.bytes.len();
         (len.saturating_add(3) / 4, Some(len))
     }
 }