feat: forward line-diffing capabilities curtesy of the similar crate. (#470)

This is a first and maybe the last step towards providing diffing
functionality, and it seems like the right choice to keep this in
similar and contribute there as needed. All algorithms are well
described and thus shouldn't be git-specific per-se, and `similar`
is the best the community has to offer.

Author: Byron

Cargo.lock

@@ -15,6 +15,7 @@ doctest = false
 git-hash = { version = "^0.9.9", path = "../git-hash" }
 git-object = { version = "^0.20.3", path = "../git-object" }
 thiserror = "1.0.32"
+similar = { version = "2.2.0", features = ["bytes"] }
 
 [dev-dependencies]
 git-odb = { path = "../git-odb" }

git-diff/Cargo.toml

@@ -4,3 +4,6 @@
 
 ///
 pub mod tree;
+
+///
+pub mod lines;

git-diff/src/lib.rs

@@ -0,0 +1,26 @@
+use git_object::bstr::BStr;
+use similar::TextDiff;
+
+/// The crate powering file diffs.
+pub use similar;
+pub use similar::Algorithm;
+
+/// Provide an iterator over the changes needed to turn `old` into `new` with `algorithm`.
+///
+/// See [the `similar` crate documentation][similar::TextDiffConfig::diff_lines()] for information on how to use the iterator.
+pub fn with<'old, 'new, 'bufs>(
+    old: &'old BStr,
+    new: &'new BStr,
+    algorithm: Algorithm,
+) -> TextDiff<'old, 'new, 'bufs, [u8]> {
+    similar::TextDiffConfig::default()
+        .algorithm(algorithm)
+        .diff_lines(old.as_ref(), new.as_ref())
+}
+
+/// Provide an iterator over the changes needed to turn `old` into `new` with Myers algorithm, the default for `git`.
+///
+/// See [the `similar` crate documentation][similar::TextDiffConfig::diff_lines()] for information on how to use the iterator.
+pub fn myers<'old, 'new, 'bufs>(old: &'old BStr, new: &'new BStr) -> TextDiff<'old, 'new, 'bufs, [u8]> {
+    with(old, new, Algorithm::Myers)
+}