feat: Add Reference::follow() as a way to peel symbolic refs step b…

…y step.

gix/src/reference/mod.rs

@@ -62,6 +62,7 @@ impl<'repo> Reference<'repo> {
     }
 }
 
+/// Peeling
 impl<'repo> Reference<'repo> {
     /// Follow all symbolic targets this reference might point to and peel the underlying object
     /// to the end of the chain, and return it.
@@ -81,6 +82,18 @@ impl<'repo> Reference<'repo> {
     pub fn into_fully_peeled_id(mut self) -> Result<Id<'repo>, peel::Error> {
         self.peel_to_id_in_place()
     }
+
+    /// Follow this symbolic reference one level and return the ref it refers to.
+    ///
+    /// Returns `None` if this is not a symbolic reference, hence the leaf of the chain.
+    pub fn follow(&self) -> Option<Result<Reference<'repo>, gix_ref::file::find::existing::Error>> {
+        self.inner.follow(&self.repo.refs).map(|res| {
+            res.map(|r| Reference {
+                inner: r,
+                repo: self.repo,
+            })
+        })
+    }
 }
 
 mod edits;

gix/tests/reference/mod.rs

@@ -23,7 +23,7 @@ mod find {
     use std::convert::TryInto;
 
     use gix_ref as refs;
-    use gix_ref::FullNameRef;
+    use gix_ref::{FullName, FullNameRef, Target};
 
     use crate::util::hex_to_id;
 
@@ -64,6 +64,25 @@ mod find {
         assert_eq!(symbolic_ref.into_fully_peeled_id()?, the_commit, "idempotency");
         Ok(())
     }
+
+    #[test]
+    fn and_follow() -> crate::Result {
+        let repo = repo()?;
+        let mut symbolic_ref = repo.find_reference("multi-link-target1")?;
+        let first_hop = Target::Symbolic(FullName::try_from("refs/tags/multi-link-target2").expect("valid"));
+        assert_eq!(symbolic_ref.target(), first_hop.to_ref());
+
+        let second_hop = Target::Symbolic(FullName::try_from("refs/remotes/origin/multi-link-target3").expect("valid"));
+        symbolic_ref = symbolic_ref.follow().expect("another hop")?;
+        assert_eq!(symbolic_ref.target(), second_hop.to_ref());
+
+        let last_hop = Target::Peeled(hex_to_id("134385f6d781b7e97062102c6a483440bfda2a03"));
+        symbolic_ref = symbolic_ref.follow().expect("another hop")?;
+        assert_eq!(symbolic_ref.target(), last_hop.to_ref());
+
+        assert!(symbolic_ref.follow().is_none(), "direct references can't be followed");
+        Ok(())
+    }
 }
 
 #[test]