Add '#' and '.' special registers

These come from Kakoune:

* '#' is the selection index register. It's read-only and produces the
  selection index numbers, 1-indexed.
* '.' is the selection contents register. It is also read-only and
  mirrors the contents of the current selections when read.

We switch the iterators returned from Selection's `fragments` and
`slices` methods to ExactSizeIterators because:

* The selection contents register can simply return the fragments
  iterator.
* ExactSizeIterator is already implemented for iterators over Vecs, so
  it's essentially free.
* The `len` method can be useful on its own.

1 files changed, 10 insertions, 2 deletions

diff --git a/helix-core/src/selection.rs b/helix-core/src/selection.rs
index 9104c209..c44685ee 100644
--- a/helix-core/src/selection.rs
+++ b/helix-core/src/selection.rs
@@ -630,11 +630,19 @@ impl Selection {
         self.transform(|range| Range::point(range.cursor(text)))
     }
 
-    pub fn fragments<'a>(&'a self, text: RopeSlice<'a>) -> impl Iterator<Item = Cow<str>> + 'a {
+    pub fn fragments<'a>(
+        &'a self,
+        text: RopeSlice<'a>,
+    ) -> impl DoubleEndedIterator<Item = Cow<'a, str>> + ExactSizeIterator<Item = Cow<str>> + 'a
+    {
         self.ranges.iter().map(move |range| range.fragment(text))
     }
 
-    pub fn slices<'a>(&'a self, text: RopeSlice<'a>) -> impl Iterator<Item = RopeSlice> + 'a {
+    pub fn slices<'a>(
+        &'a self,
+        text: RopeSlice<'a>,
+    ) -> impl DoubleEndedIterator<Item = RopeSlice<'a>> + ExactSizeIterator<Item = RopeSlice<'a>> + 'a
+    {
         self.ranges.iter().map(move |range| range.slice(text))
     }