Extract utils

backend/reconcile/src/utils/common_prefix_len.rs

@@ -0,0 +1,46 @@
+use std::ops::{Index, Range};
+
+/// Given two lookups and ranges calculates the length of the common prefix.
+/// Copied from https://github.com/mitsuhiko/similar/blob/7e15c44de11a1cd61e1149189929e189ef977fd8/src/algorithms/utils.rs
+pub fn common_prefix_len<Old, New>(
+    old: &Old,
+    old_range: Range<usize>,
+    new: &New,
+    new_range: Range<usize>,
+) -> usize
+where
+    Old: Index<usize> + ?Sized,
+    New: Index<usize> + ?Sized,
+    New::Output: PartialEq<Old::Output>,
+{
+    new_range
+        .zip(old_range)
+        .take_while(|x| new[x.0] == old[x.1])
+        .count()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use pretty_assertions::assert_eq;
+
+    #[test]
+    fn test_common_prefix_len() {
+        assert_eq!(
+            common_prefix_len("".as_bytes(), 0..0, "".as_bytes(), 0..0),
+            0
+        );
+        assert_eq!(
+            common_prefix_len("foobarbaz".as_bytes(), 0..9, "foobarblah".as_bytes(), 0..10),
+            7
+        );
+        assert_eq!(
+            common_prefix_len("foobarbaz".as_bytes(), 0..9, "blablabla".as_bytes(), 0..9),
+            0
+        );
+        assert_eq!(
+            common_prefix_len("foobarbaz".as_bytes(), 3..9, "foobarblah".as_bytes(), 3..10),
+            4
+        );
+    }
+}