Add test for rename tracking per hunk

gix-blame/src/file/function.rs

@@ -128,8 +128,6 @@ pub fn file(
             continue 'outer;
         };
 
-        // We know `first_hunk_for_suspect` can’t be `None` here because we check `is_some()`
-        // above.
         let current_file_path = first_hunk_for_suspect
             .source_file_name
             .clone()

gix-blame/tests/blame.rs

@@ -487,6 +487,47 @@ mod blame_ranges {
     }
 }
 
+mod rename_tracking {
+    use gix_blame::BlameRanges;
+
+    use crate::{Baseline, Fixture};
+
+    #[test]
+    fn source_file_name_is_tracked_per_hunk() {
+        let worktree_path = gix_testtools::scripted_fixture_read_only("make_blame_rename_tracking_repo.sh").unwrap();
+
+        let Fixture {
+            odb,
+            mut resource_cache,
+            suspect,
+        } = Fixture::for_worktree_path(worktree_path.to_path_buf()).unwrap();
+
+        let source_file_name = "after-rename.txt";
+        let lines_blamed = gix_blame::file(
+            &odb,
+            suspect,
+            None,
+            &mut resource_cache,
+            source_file_name.into(),
+            gix_blame::Options {
+                diff_algorithm: gix_diff::blob::Algorithm::Histogram,
+                range: BlameRanges::default(),
+                since: None,
+                rewrites: Some(gix_diff::Rewrites::default()),
+            },
+        )
+        .unwrap()
+        .entries;
+
+        assert_eq!(lines_blamed.len(), 3);
+
+        let git_dir = worktree_path.join(".git");
+        let baseline = Baseline::collect(git_dir.join("after-rename.baseline"), source_file_name.into()).unwrap();
+
+        pretty_assertions::assert_eq!(lines_blamed, baseline);
+    }
+}
+
 fn fixture_path() -> PathBuf {
     gix_testtools::scripted_fixture_read_only("make_blame_repo.sh").unwrap()
 }

gix-blame/tests/fixtures/make_blame_rename_tracking_repo.sh

@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+set -eu -o pipefail
+
+git init -q
+git config --local diff.algorithm histogram
+
+git config merge.ff false
+
+git checkout -q -b main
+
+seq 1 4 > before-rename.txt
+git add before-rename.txt
+git commit -q -m c1
+
+mv before-rename.txt after-rename.txt
+git add before-rename.txt after-rename.txt
+git commit -q -m c2
+
+seq 1 5 > after-rename.txt
+git add after-rename.txt
+git commit -q -m c3
+
+git checkout -b different-branch
+git reset --hard HEAD~2
+
+seq 0 4 > before-rename.txt
+git add before-rename.txt
+git commit -q -m c10
+
+mv before-rename.txt after-rename.txt
+git add before-rename.txt after-rename.txt
+git commit -q -m c11
+
+git checkout main
+git merge different-branch || true
+
+git blame --porcelain after-rename.txt > .git/after-rename.baseline