Re-use `HEAD` reference if it exists

Since the `HEAD` reference is trusted (we set it locally), use that
when possible, instead of re-computing it.

Signed-off-by: Alexis Sellier <alexis@radicle.xyz>

radicle/src/git.rs

@@ -31,8 +31,12 @@ pub const PROTOCOL_PORT: u16 = 9418;
 
 #[derive(thiserror::Error, Debug)]
 pub enum RefError {
-    #[error("invalid ref name '{0}'")]
-    InvalidName(format::RefString),
+    #[error("ref name is not valid UTF-8")]
+    InvalidName,
+    #[error("unexpected symbolic ref: {0}")]
+    Symbolic(RefString),
+    #[error("unexpected unqualified ref: {0}")]
+    Unqualified(RefString),
     #[error("invalid ref format: {0}")]
     Format(#[from] format::Error),
     #[error("expected ref to begin with 'refs/namespaces' but found '{0}'")]
@@ -67,8 +71,20 @@ pub mod refs {
     /// Where project information is kept.
     pub static IDENTITY_BRANCH: Lazy<RefString> = Lazy::new(|| refname!("radicle/id"));
 
-    pub mod storage {
+    /// Try to get a qualified reference from a generic reference.
+    pub fn qualified_from<'a>(r: &'a git2::Reference) -> Result<(Qualified<'a>, Oid), RefError> {
+        let name = r.name().ok_or(RefError::InvalidName)?;
+        let refstr = RefStr::try_from_str(name)?;
+        let target = r
+            .target()
+            .ok_or_else(|| RefError::Symbolic(refstr.to_owned()))?;
+        let qualified = Qualified::from_refstr(refstr)
+            .ok_or_else(|| RefError::Unqualified(refstr.to_owned()))?;
 
+        Ok((qualified, target.into()))
+    }
+
+    pub mod storage {
         use super::*;
 
         /// Create the [`Namespaced`] `branch` under the `remote` namespace, i.e.
@@ -157,7 +173,7 @@ where
     match input.to_namespaced() {
         None => {
             let refname = Qualified::from_refstr(input)
-                .ok_or_else(|| RefError::InvalidName(input.to_owned()))?;
+                .ok_or_else(|| RefError::Unqualified(input.to_owned()))?;
 
             Ok((None, refname))
         }

radicle/src/rad.rs

@@ -154,15 +154,13 @@ pub fn fork<G: Signer, S: storage::WriteStorage>(
 ) -> Result<(), ForkError> {
     let me = signer.public_key();
     let repository = storage.repository(proj)?;
-    let (canonical_id, project) = repository.project_identity()?;
-    let (canonical_head, _) = repository.head()?;
+    // TODO: We should get the id branch pointer from a stored canonical reference.
+    let (canonical_id, _) = repository.project_identity()?;
+    let (canonical_branch, canonical_head) = repository.head()?;
     let raw = repository.raw();
 
-    // TODO: We should only get the project HEAD once we've stored the canonical identity
-    // branch on disk. This way it can use what we stored, instead of recomputing it.
-
     raw.reference(
-        &git::refs::storage::branch(me, &project.default_branch),
+        &canonical_branch.with_namespace(me.into()),
         *canonical_head,
         false,
         &format!("creating default branch for {me}"),
@@ -353,7 +351,7 @@ mod tests {
             .unwrap();
 
         let project_repo = storage.repository(proj).unwrap();
-        let (head, _) = project_repo.head().unwrap();
+        let (_, head) = project_repo.head().unwrap();
 
         // Test canonical refs.
         assert_eq!(project_repo.raw().refname_to_id("HEAD").unwrap(), *head);

radicle/src/storage.rs

@@ -242,10 +242,20 @@ pub trait ReadRepository {
 
     fn blob_at<'a>(&'a self, oid: Oid, path: &'a Path) -> Result<git2::Blob<'a>, git_ext::Error>;
 
-    /// Get the canonical head of this repository.
+    /// Get the head of this repository.
+    ///
+    /// Returns the value of `HEAD` if it is set, otherwise computes the canonical head
+    /// using [`ReadRepository::canonical_head`].
     ///
     /// Returns the [`Oid`] as well as the qualified reference name.
-    fn head(&self) -> Result<(Oid, Qualified), ProjectError>;
+    fn head(&self) -> Result<(Qualified, Oid), ProjectError>;
+
+    /// Compute the canonical head of this repository.
+    ///
+    /// Ignores any existing `HEAD` reference.
+    ///
+    /// Returns the [`Oid`] as well as the qualified reference name.
+    fn canonical_head(&self) -> Result<(Qualified, Oid), ProjectError>;
 
     /// Get the `reference` for the given `remote`.
     ///

radicle/src/storage/git.rs

@@ -487,10 +487,18 @@ impl ReadRepository for Repository {
         Repository::project(self)
     }
 
-    fn head(&self) -> Result<(Oid, Qualified), ProjectError> {
-        // TODO: We shouldn't need to re-construct the history here; we should use the cached
-        // document head of the "trusted" (local) user for this project.
-        // In the `fork` function for example, we call Repository::project_identity again,
+    fn head(&self) -> Result<(Qualified, Oid), ProjectError> {
+        // If `HEAD` is already set locally, just return that.
+        if let Ok(head) = self.backend.head() {
+            if let Ok((name, oid)) = git::refs::qualified_from(&head) {
+                return Ok((name.to_owned(), oid));
+            }
+        }
+        self.canonical_head()
+    }
+
+    fn canonical_head(&self) -> Result<(Qualified, Oid), ProjectError> {
+        // TODO: In the `fork` function for example, we call Repository::project_identity again,
         // This should only be necessary once.
         let (_, project) = self.project_identity()?;
         let branch_ref = Qualified::from(lit::refs_heads(&project.default_branch));
@@ -509,7 +517,7 @@ impl ReadRepository for Repository {
             heads => raw.merge_base_many(heads),
         }?;
 
-        Ok((oid.into(), branch_ref))
+        Ok((branch_ref, oid.into()))
     }
 }
 
@@ -631,7 +639,7 @@ impl WriteRepository for Repository {
 
     fn set_head(&self) -> Result<Oid, ProjectError> {
         let head_ref = refname!("HEAD");
-        let (head, branch_ref) = self.head()?;
+        let (branch_ref, head) = self.canonical_head()?;
 
         log::debug!("Setting ref {:?} -> {:?}", &branch_ref, head);
         self.raw()

radicle/src/test/storage.rs

@@ -78,7 +78,11 @@ impl ReadRepository for MockRepository {
         Ok(true)
     }
 
-    fn head(&self) -> Result<(Oid, fmt::Qualified), ProjectError> {
+    fn head(&self) -> Result<(fmt::Qualified, Oid), ProjectError> {
+        todo!()
+    }
+
+    fn canonical_head(&self) -> Result<(fmt::Qualified, Oid), ProjectError> {
         todo!()
     }