feat: support workspace filters when fetching them from the object da…

…tabase

gix-diff/Cargo.toml

@@ -13,7 +13,7 @@ autotests = false
 [features]
 default = ["blob"]
 ## Enable diffing of blobs using imara-diff, which also allows for a generic rewrite tracking implementation.
-blob = ["dep:imara-diff"]
+blob = ["dep:imara-diff", "dep:gix-filter"]
 ## Data structures implement `serde::Serialize` and `serde::Deserialize`.
 serde = ["dep:serde", "gix-hash/serde", "gix-object/serde"]
 ## Make it possible to compile to the `wasm32-unknown-unknown` target.
@@ -25,6 +25,7 @@ doctest = false
 [dependencies]
 gix-hash = { version = "^0.13.1", path = "../gix-hash" }
 gix-object = { version = "^0.38.0", path = "../gix-object" }
+gix-filter = { version = "^0.6.0", path = "../gix-filter", optional = true }
 
 thiserror = "1.0.32"
 imara-diff = { version = "0.1.3", optional = true }

gix-diff/src/rewrites/tracker.rs

@@ -19,9 +19,24 @@ pub enum ChangeKind {
     Addition,
 }
 
+/// A trait to help access the worktree version of a file, if present.
+pub trait WorktreeBlob {
+    /// Write the contents of the file, executable or link (i.e. the link target itself) at
+    /// `rela_path` to the initially empty `buf`.
+    /// `is_source` is `true` if this is the blob for the source of a rewrite (copy or rename). Otherwise it is the
+    /// destination.
+    ///
+    /// Return `std::io::ErrorKind::NotFound` if the file is not available in the working tree, which will make the
+    /// implementation to extract it from the object database instead and convert it to its working-tree counterpart.
+    fn worktree_blob(&mut self, rela_path: &BStr, buf: &mut Vec<u8>, is_source: bool) -> std::io::Result<()>;
+}
+
 /// A trait providing all functionality to abstract over the concept of a change, as seen by the [`Tracker`].
 pub trait Change: Clone {
     /// Return the hash of this change for identification.
+    ///
+    /// Note that this is the id of the object as stored in `git`, i.e. it must have gone through workspace
+    /// conversions.
     fn id(&self) -> &gix_hash::oid;
     /// Return the kind of this change.
     fn kind(&self) -> ChangeKind;
@@ -162,10 +177,14 @@ impl<T: Change> Tracker<T> {
     ///
     /// `cb(destination, source)` is called for each item, either with `Some(source)` if it's
     /// the destination of a copy or rename, or with `None` for source if no relation to other
-    /// items in the tracked set exist.
+    /// items in the tracked set exist, which is like saying 'no rename or rewrite or copy' happened.
     ///
     /// `objects` is used to access blob data for similarity checks if required and is taken directly from the object database.
-    /// Worktree filters and diff conversions will be applied afterwards automatically.
+    /// Worktree filters and text conversions will be applied afterwards automatically.
+    ///
+    /// Use `worktree_filter` to obtain working-tree versions of files present on disk before diffing to see if rewrites happened,
+    /// with text-conversions being applied afterwards.
+    /// If it indicates no such file exists, it's read from objects instead.
     ///
     /// `push_source_tree(push_fn: push(change, location))` is a function that is called when the entire tree of the source
     /// should be added as modifications by calling `push` repeatedly to use for perfect copy tracking. Note that `push`
@@ -174,6 +193,7 @@ impl<T: Change> Tracker<T> {
         &mut self,
         mut cb: impl FnMut(visit::Destination<'_, T>, Option<visit::Source<'_>>) -> crate::tree::visit::Action,
         objects: &dyn gix_object::Find,
+        worktree_filter: &mut gix_filter::Pipeline,
         mut push_source_tree: PushSourceTreeFn,
     ) -> Result<Outcome, emit::Error>
     where