fix: similarity detection

Previously it would incorrectly count only the last batch of removed bytes, and now it will count all of them. This leads to realistic results with complex diffs, even though it's probably still not en-par with Git which uses more complex heuristics.

gix-diff/src/rewrites/tracker.rs

@@ -561,10 +561,10 @@ mod diff {
         type Out = usize;
 
         fn process_change(&mut self, before: Range<u32>, _after: Range<u32>) {
-            self.removed_bytes = self.input.before[before.start as usize..before.end as usize]
+            self.removed_bytes += self.input.before[before.start as usize..before.end as usize]
                 .iter()
                 .map(|token| self.input.interner[*token].len())
-                .sum();
+                .sum::<usize>();
         }
 
         fn finish(self) -> Self::Out {

gix/tests/object/tree/diff.rs

@@ -175,6 +175,7 @@ fn tree_named(repo: &gix::Repository, rev_spec: impl AsRef<str>) -> gix::Tree {
 }
 
 mod track_rewrites {
+    use std::collections::HashMap;
     use std::convert::Infallible;
 
     use gix::{
@@ -398,34 +399,27 @@ mod track_rewrites {
             // It's like the fixture doesn't get setup correctly.
             return Ok(());
         }
+
+        let mut expected = HashMap::<&BStr, (&BStr, u32)>::new();
+        expected.insert(
+            "cli/src/commands/file/chmod.rs".into(),
+            ("cli/src/commands/chmod.rs".into(), 90),
+        );
+        expected.insert(
+            "cli/src/commands/file/print.rs".into(),
+            ("cli/src/commands/cat.rs".into(), 90),
+        );
+        expected.insert(
+            "cli/tests/test_file_chmod_command.rs".into(),
+            ("cli/tests/test_chmod_command.rs".into(), 88),
+        );
+        expected.insert(
+            "cli/tests/test_file_print_command.rs".into(),
+            ("cli/tests/test_cat_command.rs".into(), 77),
+        );
+
         let from = tree_named(&repo, "@~1");
         let to = tree_named(&repo, "@");
-
-        let mut count = 0;
-        let expected_location = [
-            "cli",
-            "cli/src",
-            "cli/tests",
-            "cli/src/commands",
-            "cli/src/commands/file",
-            "cli/src/commands/file/print.rs",
-            "cli/tests/test_file_print_command.rs",
-            "cli/src/commands/file/chmod.rs",
-            "cli/src/commands/file/mod.rs",
-            "cli/tests/test_file_chmod_command.rs",
-            "CHANGELOG.md",
-            "cli/src/commands/mod.rs",
-            "cli/tests/cli-reference@.md.snap",
-            "cli/tests/runner.rs",
-            "cli/tests/test_acls.rs",
-            "cli/tests/test_diffedit_command.rs",
-            "cli/tests/test_fix_command.rs",
-            "cli/tests/test_global_opts.rs",
-            "cli/tests/test_move_command.rs",
-            "cli/tests/test_new_command.rs",
-            "cli/tests/test_squash_command.rs",
-            "cli/tests/test_unsquash_command.rs",
-        ];
         let out = from
             .changes()?
             .track_path()
@@ -441,48 +435,24 @@ mod track_rewrites {
                 .into(),
             )
             .for_each_to_obtain_tree(&to, |change| -> Result<_, Infallible> {
-                // TODO: all rewrites here don't match what Git produces right now.
-                // dbg!(change);
-                assert_eq!(change.location, expected_location[count]);
-                match count {
-                    0 | 1 | 2 | 3 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 => {
-                        assert!(
-                            matches!(change.event, Event::Modification { .. }),
-                            "ignore modifications"
-                        );
-                    }
-                    4 => {
-                        assert!(matches!(change.event, Event::Addition { entry_mode, .. } if entry_mode.is_tree()));
-                        assert_eq!(change.location, "cli/src/commands/file");
-                    }
-                    5 => {
-                        assert_eq!(change.location, "cli/src/commands/file/print.rs");
-                        assert!(matches!(change.event, Event::Rewrite {source_location, ..} if source_location == "cli/tests/test_cat_command.rs"));
-                    }
-                    6 => {
-                        assert_eq!(change.location, "cli/tests/test_file_print_command.rs");
-                        assert!(matches!(change.event, Event::Rewrite {source_location, ..} if source_location == "cli/tests/test_chmod_command.rs"));
-                    }
-                    7 => {
-                        assert_eq!(change.location, "cli/src/commands/file/chmod.rs");
-                        assert!(matches!(change.event, Event::Rewrite {source_location, ..} if source_location == "cli/src/commands/chmod.rs"));
-                    }
-                    8 => {
-                        assert_eq!(change.location, "cli/src/commands/file/mod.rs");
-                        assert!(matches!(change.event, Event::Rewrite {source_location, ..} if source_location == "cli/src/commands/cat.rs"));
-                    }
-                    9 => {
-                        assert_eq!(change.location, "cli/tests/test_file_chmod_command.rs");
-                        assert!(matches!(change.event, Event::Rewrite {source_location, ..} if source_location == "cli/tests/test_immutable_commits.rs"));
-                    }
-                    n => unreachable!("unexpected call: {n}"),
-                };
-                count += 1;
+                if let Event::Rewrite {
+                    source_location,
+                    diff: Some(diff),
+                    ..
+                } = change.event
+                {
+                    // Round to percentage points to avoid floating point error.
+                    let similarity = (diff.similarity * 100.0) as u32;
+                    let v = expected.remove(change.location);
+                    assert_eq!(v, Some((source_location, similarity)));
+                }
                 Ok(Default::default())
             })?;
+
+        assert_eq!(expected, HashMap::new());
         let out = out.rewrites.expect("tracking enabled");
         assert_eq!(
-            out.num_similarity_checks, 8,
+            out.num_similarity_checks, 21,
             "this probably increases once the algorithm improves"
         );
         assert_eq!(