core: implement log_file

Implement the log_file method in gitoxide-core, which allows performing
path-delimited log commands. With the new changed paths bloom filter, it
is not possible to perform this operation very efficiently.

Author: vmg

gitoxide-core/src/repository/log.rs

@@ -1,5 +1,4 @@
-use anyhow::bail;
-use gix::bstr::{BString, ByteSlice};
+use gix::bstr::{BStr, BString, ByteSlice};
 
 pub fn log(mut repo: gix::Repository, out: &mut dyn std::io::Write, path: Option<BString>) -> anyhow::Result<()> {
     repo.object_cache_size_if_unset(repo.compute_object_cache_size_for_tree_diffs(&**repo.index_or_empty()?));
@@ -25,8 +24,20 @@ fn log_all(repo: gix::Repository, out: &mut dyn std::io::Write) -> Result<(), an
     Ok(())
 }
 
-fn log_file(_repo: gix::Repository, _out: &mut dyn std::io::Write, _path: BString) -> anyhow::Result<()> {
-    bail!("File-based lookup isn't yet implemented in a way that is competitively fast");
+fn log_file(repo: gix::Repository, out: &mut dyn std::io::Write, path: BString) -> anyhow::Result<()> {
+    let path = gix::path::to_unix_separators_on_windows(path.as_bstr()).into_owned();
+    let head = repo.head()?.peel_to_commit()?;
+    let cache = repo.commit_graph_if_enabled()?;
+    let topo = gix::traverse::commit::topo::Builder::from_iters(&repo.objects, [head.id], None::<Vec<gix::ObjectId>>)
+        .build()?;
+
+    for info in topo {
+        let info = info?;
+        if commit_changes_path(&repo, cache.as_ref(), &info, path.as_ref())? {
+            write_info(&repo, &mut *out, &info)?;
+        }
+    }
+    Ok(())
 }
 
 fn write_info(
@@ -48,3 +59,41 @@ fn write_info(
 
     Ok(())
 }
+
+fn commit_changes_path(
+    repo: &gix::Repository,
+    cache: Option<&gix::commitgraph::Graph>,
+    info: &gix::traverse::commit::Info,
+    path: &BStr,
+) -> anyhow::Result<bool> {
+    let commit = repo.find_commit(info.id)?;
+    let commit_tree = commit.tree()?;
+    let commit_entry = lookup_path_entry(&commit_tree, path)?;
+
+    if info.parent_ids.is_empty() {
+        return Ok(commit_entry.is_some());
+    }
+
+    for (index, parent_id) in info.parent_ids.iter().enumerate() {
+        if index == 0 && cache.and_then(|graph| graph.maybe_contains_path_by_id(info.id, path)) == Some(false) {
+            continue;
+        }
+
+        let parent = repo.find_commit(*parent_id)?;
+        let parent_tree = parent.tree()?;
+        let parent_entry = lookup_path_entry(&parent_tree, path)?;
+        if commit_entry != parent_entry {
+            return Ok(true);
+        }
+    }
+
+    Ok(false)
+}
+
+fn lookup_path_entry(
+    tree: &gix::Tree<'_>,
+    path: &BStr,
+) -> anyhow::Result<Option<(gix::objs::tree::EntryMode, gix::ObjectId)>> {
+    let entry = tree.lookup_entry(path.split(|b| *b == b'/'))?;
+    Ok(entry.map(|entry| (entry.mode(), entry.object_id())))
+}