Add test for source file name tracking per hunk

This is a test case for the issue fixed in
7435ed5. The issue was related to the
fact that, before the fix, `source_file_name` was only tracked globally,
as opposed to locally, i. e. on a per-hunk basis.

The test case constructs a repository that has the same rename twice, in
two different branches. Tracking `source_file_name` globally is
insufficient to capture this history which is why this test fails
without the fix.

Author: cruessler

gix-blame/tests/blame.rs

@@ -487,6 +487,48 @@ 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: gix_object::bstr::BString = "after-rename.txt".into();
+
+        let lines_blamed = gix_blame::file(
+            &odb,
+            suspect,
+            None,
+            &mut resource_cache,
+            source_file_name.as_ref(),
+            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).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
+
+echo -e "line 1\nline 2\nline 3\nline 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
+
+echo -e "line 1\nline 2\nline 3\nline 4\nline 5" > after-rename.txt
+git add after-rename.txt
+git commit -q -m c3
+
+git checkout -b different-branch
+git reset --hard HEAD~2
+
+echo -e "line 0\nline 1\nline 2\nline 3\nline 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