Implement :<path> parsing (#427)

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

@@ -95,7 +95,10 @@ pub enum PeelTo<'a> {
     /// The path to drill into as seen relative to the current tree-ish.
     ///
     /// Note that the path can be relative, and `./` and `../` prefixes are seen as relative to the current
-    /// working directory
+    /// working directory.
+    ///
+    /// The path may be empty, which makes it refer to the tree at the current revision, similar to `^{tree}`.
+    /// Note that paths like `../` are valid and refer to a tree as seen relative to the current working directory.
     Path(&'a BStr),
 }
 

git-revision/src/spec/parse/function.rs

@@ -300,7 +300,12 @@ fn navigate<'a>(input: &'a BStr, delegate: &mut impl Delegate) -> Result<&'a BSt
                         .ok_or(Error::Delegate)?;
                 }
             }
-            b':' => todo!(":"),
+            b':' => {
+                delegate
+                    .peel_until(delegate::PeelTo::Path(input[cursor..].as_bstr()))
+                    .ok_or(Error::Delegate)?;
+                return Ok("".into());
+            }
             _ => return Ok(input[cursor - 1..].as_bstr()),
         }
     }

git-revision/tests/spec/parse/navigate.rs

@@ -3,7 +3,6 @@ mod colon_symbol {
     use git_revision::spec::parse::delegate::Traversal;
 
     #[test]
-    #[ignore]
     fn paths_consume_all_remaining_input_as_they_refer_to_blobs() {
         let rec = parse("@:../relative/path...@^^~~");
 
@@ -24,13 +23,22 @@ mod colon_symbol {
         let rec = parse("@:absolute/path^{tree}");
         assert_eq!(
             rec.peel_to,
-            vec![PeelTo::Path("absolute/path^{object}".into())],
+            vec![PeelTo::Path("absolute/path^{tree}".into())],
             "this includes useful navigation like assertion of trees/blobs, we may make this possible in future but for now are as open as git"
         );
     }
 
     #[test]
-    #[ignore]
+    fn empty_paths_refer_to_the_root_tree() {
+        let rec = parse("@:");
+
+        assert!(rec.kind.is_none());
+        assert_eq!(rec.get_ref(0), "HEAD");
+        assert_eq!(rec.peel_to, vec![PeelTo::Path("".into())]);
+        assert_eq!(rec.calls, 2);
+    }
+
+    #[test]
     fn paths_have_to_be_last_but_stack_with_other_navigation() {
         let rec = parse("HEAD@{1}~10^2^{commit}:README.md");