Implement FoldMap's folds using a SumTree

This required passing a `Context` object to `Summary` and introducing a
new `SeekDimension` trait that allows comparing two dimensions and pass
an additional context object.

zed/src/util.rs

@@ -30,37 +30,6 @@ where
     }
 }
 
-pub fn find_insertion_index<'a, F, T, E>(slice: &'a [T], mut f: F) -> Result<usize, E>
-where
-    F: FnMut(&'a T) -> Result<Ordering, E>,
-{
-    use Ordering::*;
-
-    let s = slice;
-    let mut size = s.len();
-    if size == 0 {
-        return Ok(0);
-    }
-    let mut base = 0usize;
-    while size > 1 {
-        let half = size / 2;
-        let mid = base + half;
-        // mid is always in [0, size), that means mid is >= 0 and < size.
-        // mid >= 0: by definition
-        // mid < size: mid = size / 2 + size / 4 + size / 8 ...
-        let cmp = f(unsafe { s.get_unchecked(mid) })?;
-        base = if cmp == Greater { base } else { mid };
-        size -= half;
-    }
-    // base is always in [0, size) because base <= mid.
-    let cmp = f(unsafe { s.get_unchecked(base) })?;
-    if cmp == Equal {
-        Ok(base)
-    } else {
-        Ok(base + (cmp == Less) as usize)
-    }
-}
-
 pub struct RandomCharIter<T: Rng>(T);
 
 impl<T: Rng> RandomCharIter<T> {
@@ -85,14 +54,6 @@ impl<T: Rng> Iterator for RandomCharIter<T> {
 mod tests {
     use super::*;
 
-    #[test]
-    fn test_find_insertion_index() {
-        assert_eq!(
-            find_insertion_index(&[0, 4, 8], |probe| Ok::<Ordering, ()>(probe.cmp(&2))),
-            Ok(1)
-        );
-    }
-
     #[test]
     fn test_extend_sorted() {
         let mut vec = vec![];