Merge pull request #91 from distil/fix_all_same

fix: Don't create overlapping prefix_eq/suffix_eq in the LCS

Author: Marwes

diffus-derive-test/src/lib.rs

@@ -91,6 +91,33 @@ mod test {
         }
     }
 
+    #[test]
+    fn changed_contents() {
+        let left = vec![Identified { id: 1, value: 0 }];
+        let right = vec![Identified { id: 1, value: 1 }];
+
+        let diff = left.diff(&right);
+
+        use edit::{self, collection};
+
+        if let edit::Edit::Change(diff) = diff {
+            let diff = diff.into_iter().collect::<Vec<_>>();
+
+            assert_eq!(diff.len(), 1);
+
+            if let &collection::Edit::Change(EditedIdentified {
+                id: edit::Edit::Copy(&1),
+                value: edit::Edit::Change((&0, &1)),
+            }) = &diff[0]
+            {
+            } else {
+                unreachable!()
+            }
+        } else {
+            unreachable!()
+        }
+    }
+
     #[derive(Diffus)]
     enum NestedTest {
         T { test: Test },

diffus/src/lcs.rs

@@ -28,12 +28,25 @@ where
     I: DoubleEndedIterator<Item = T>,
     J: DoubleEndedIterator<Item = T>,
 {
-    let prefix_eq = x().zip(y()).take_while(|(x, y)| x.same(y)).count();
-    let suffix_eq = x()
-        .rev()
-        .zip(y().rev())
+    let mut x_iter = x();
+    let mut y_iter = y();
+    let prefix_eq = x_iter
+        .by_ref()
+        .zip(y_iter.by_ref())
         .take_while(|(x, y)| x.same(y))
         .count();
+    // Only check the suffix if we did not consume the entirety of either of the iterators
+    // (If one of them are consumed, we would double count elements)
+    let check_suffix = x_len.min(y_len) != prefix_eq;
+    let suffix_eq = if check_suffix {
+        x_iter
+            .rev()
+            .zip(y_iter.rev())
+            .take_while(|(x, y)| x.same(y))
+            .count()
+    } else {
+        0
+    };
 
     let width = x_len.saturating_sub(prefix_eq + suffix_eq) + 1;
     let height = y_len.saturating_sub(prefix_eq + suffix_eq) + 1;