test for nth prior checkout (#427)

git-repository/src/revision/spec/parse/delegate.rs

@@ -283,7 +283,7 @@ impl<'repo> delegate::Revision for Delegate<'repo> {
 
     fn sibling_branch(&mut self, _kind: SiblingBranch) -> Option<()> {
         self.unset_disambiguate_call();
-        todo!()
+        todo!("once remote handling and ref-specs are fleshed out much more")
     }
 }
 

git-repository/tests/fixtures/make_rev_spec_parse_repos.sh

@@ -370,4 +370,11 @@ git init complex_graph
   baseline "j"
   baseline "b^3^2"
   baseline "a^^3^2"
+
+  baseline "@{-1}"
+  baseline "@{-2}"
+  baseline "@{-3}"
+  baseline "@{-4}"
+  baseline "@{-5}"
+  baseline "@{-6}"
 )

git-repository/tests/revision/spec/from_bytes/mod.rs

@@ -8,7 +8,9 @@ pub use util::*;
 mod ambiguous;
 mod regex;
 
+mod reflog;
 mod traverse;
+
 mod index {
     use crate::revision::spec::from_bytes::{parse_spec, repo};
     use git_repository::prelude::ObjectIdExt;

git-repository/tests/revision/spec/from_bytes/reflog.rs

@@ -0,0 +1,16 @@
+use crate::revision::spec::from_bytes::{parse_spec, repo};
+
+#[test]
+#[ignore]
+fn nth_prior_checkout() {
+    let repo = repo("complex_graph").unwrap();
+
+    for spec in ["@{-1}", "@{-2}", "@{-3}", "@{-4}", "@{-5}"] {
+        assert!(parse_spec(spec, &repo).is_ok(), "spec {} should be valid", spec);
+    }
+
+    assert_eq!(
+        parse_spec("@{-6}", &repo).unwrap_err().to_string(),
+        "HEAD has 5 prior checkouts and checkout 6 is out of range"
+    );
+}