don't degenerate information about the unborn fetch ref's path. (#450)

Previously we assumed this could only happen for `HEAD`, but in fact
dangling symrefs are possible and they might end up in the server
response that way.

Author: Byron

git-protocol/src/fetch/refs/mod.rs

@@ -77,9 +77,12 @@ pub enum Ref {
         /// The hash of the object the `target` ref points to.
         object: git_hash::ObjectId,
     },
-    /// `HEAD` is unborn on the remote and just points to the initial, unborn branch.
+    /// A ref is unborn on the remote and just points to the initial, unborn branch, as is the case in a newly initialized repository
+    /// or dangling symbolic refs.
     Unborn {
-        /// The path of the ref the symbolic ref points to, like `refs/heads/main`.
+        /// The name at which the ref is located, typically `HEAD`.
+        full_ref_name: BString,
+        /// The path of the ref the symbolic ref points to, like `refs/heads/main`, even though the `target` does not yet exist.
         target: BString,
     },
 }
@@ -100,7 +103,10 @@ impl Ref {
                 tag: object,
                 object: peeled,
             } => (full_ref_name.as_ref(), Some(object), Some(peeled)),
-            Ref::Unborn { target: _ } => ("HEAD".into(), None, None),
+            Ref::Unborn {
+                full_ref_name,
+                target: _,
+            } => (full_ref_name.as_ref(), None, None),
         }
     }
 }

git-protocol/src/fetch/refs/shared.rs

@@ -207,7 +207,10 @@ pub(in crate::fetch::refs) fn parse_v2(line: &str) -> Result<Ref, Error> {
                                         object: id,
                                         target: name.into(),
                                     },
-                                    None => Ref::Unborn { target: name.into() },
+                                    None => Ref::Unborn {
+                                        full_ref_name: path.into(),
+                                        target: name.into(),
+                                    },
                                 },
                             },
                             _ => {

git-protocol/src/fetch/tests/refs.rs

@@ -8,6 +8,7 @@ async fn extract_references_from_v2_refs() {
     let input = &mut "808e50d724f604f69ab93c6da2919c014667bedb HEAD symref-target:refs/heads/main
 808e50d724f604f69ab93c6da2919c014667bedb MISSING_NAMESPACE_TARGET symref-target:(null)
 unborn HEAD symref-target:refs/heads/main
+unborn refs/heads/symbolic symref-target:refs/heads/target
 808e50d724f604f69ab93c6da2919c014667bedb refs/heads/main
 7fe1b98b39423b71e14217aa299a03b7c937d656 refs/tags/foo peeled:808e50d724f604f69ab93c6da2919c014667bedb
 7fe1b98b39423b71e14217aa299a03b7c937d6ff refs/tags/blaz
@@ -29,8 +30,13 @@ unborn HEAD symref-target:refs/heads/main
                 object: oid("808e50d724f604f69ab93c6da2919c014667bedb")
             },
             Ref::Unborn {
+                full_ref_name: "HEAD".into(),
                 target: "refs/heads/main".into(),
             },
+            Ref::Unborn {
+                full_ref_name: "refs/heads/symbolic".into(),
+                target: "refs/heads/target".into(),
+            },
             Ref::Direct {
                 full_ref_name: "refs/heads/main".into(),
                 object: oid("808e50d724f604f69ab93c6da2919c014667bedb")