fetch: allow fetch of annotated tags

If an ancestry check of an annotated tag was triggered then the fetch
from that peer would fail. This is due to `graph_ahead_behind` only
working for commit-ish objects.

To allow for annotated tags, and other object that peel to commits,
the check now peels the two objects to commits before getting their
`Oid`s. The call to `graph_ahead_behind` can take these two `Oid`s
instead.

A test for annotated tags is included as part of the `examples/git`
suite in the CLI tests.

Signed-off-by: Fintan Halpenny <fintan.halpenny@gmail.com>
X-Clacks-Overhead: GNU Terry Pratchett

radicle-cli/examples/git/git-tag.md

@@ -0,0 +1,70 @@
+Alice creates an annotated tag and pushed to her `rad` remote:
+
+``` ~alice
+$ touch LICENSE
+$ git add LICENSE
+$ git commit -am "Add LICENSE"
+[master 62d19fd] Add LICENSE
+ 1 file changed, 0 insertions(+), 0 deletions(-)
+ create mode 100644 LICENSE
+$ git tag v1.0 -a -m "Release v1.0"
+```
+
+``` ~alice (stderr)
+$ git push rad v1.0 --tags
+✓ Synced with 1 node(s)
+To rad://z42hL2jL4XNk6K8oHQaSWfMgCL7ji/z6MknSLrJoTcukLrE435hVNQT4JUhbvWLX4kUzqkEStBU8Vi
+ * [new tag]         v1.0 -> v1.0
+```
+
+Bob fetches the tag from Alice, by adding her as a remote:
+
+``` ~bob
+$ cd heartwood
+$ rad remote add z6MknSLrJoTcukLrE435hVNQT4JUhbvWLX4kUzqkEStBU8Vi --name alice
+✓ Follow policy updated for z6MknSLrJoTcukLrE435hVNQT4JUhbvWLX4kUzqkEStBU8Vi (alice)
+✓ Fetching rad:z42hL2jL4XNk6K8oHQaSWfMgCL7ji from z6MknSL…StBU8Vi..
+✓ Remote alice added
+✓ Remote-tracking branch alice/master created for z6MknSL…StBU8Vi
+```
+
+Bob is able to fetch Alice's tag into his working copy by using the
+`--tags` flag:
+
+``` ~bob (stderr)
+$ git fetch alice --tags
+From rad://z42hL2jL4XNk6K8oHQaSWfMgCL7ji/z6MknSLrJoTcukLrE435hVNQT4JUhbvWLX4kUzqkEStBU8Vi
+ * [new tag]         v1.0       -> v1.0
+```
+
+Alice forcefully creates a new version of the tag (let's say she made
+a mistake):
+
+``` ~alice
+$ git commit --allow-empty -m "Release: v1.0"
+[master 8260c04] Release: v1.0
+$ git tag v1.0 -f -a -m "Release v1.0"
+Updated tag 'v1.0' (was be18ed6)
+```
+
+``` ~alice (stderr)
+$ git push rad v1.0 -f
+✓ Synced with 1 node(s)
+To rad://z42hL2jL4XNk6K8oHQaSWfMgCL7ji/z6MknSLrJoTcukLrE435hVNQT4JUhbvWLX4kUzqkEStBU8Vi
+ + be18ed6...9dbdebc v1.0 -> v1.0 (forced update)
+```
+
+We ensure that Bob is still able to fetch from Alice and get the new
+update of the tag:
+
+``` ~bob
+$ rad sync -f
+✓ Fetching rad:z42hL2jL4XNk6K8oHQaSWfMgCL7ji from z6MknSL…StBU8Vi..
+✓ Fetched repository from 1 seed(s)
+```
+
+``` ~bob (stderr)
+$ git fetch alice --tags -f
+From rad://z42hL2jL4XNk6K8oHQaSWfMgCL7ji/z6MknSLrJoTcukLrE435hVNQT4JUhbvWLX4kUzqkEStBU8Vi
+ t [tag update]      v1.0       -> v1.0
+```

radicle-cli/tests/commands.rs

@@ -2317,6 +2317,51 @@ fn git_push_and_fetch() {
     .unwrap();
 }
 
+#[test]
+fn git_tag() {
+    let mut environment = Environment::new();
+    let alice = environment.node(Config::test(Alias::new("alice")));
+    let bob = environment.node(Config::test(Alias::new("bob")));
+    let working = environment.tmp().join("working");
+
+    fixtures::repository(working.join("alice"));
+
+    test(
+        "examples/rad-init.md",
+        working.join("alice"),
+        Some(&alice.home),
+        [],
+    )
+    .unwrap();
+
+    let alice = alice.spawn();
+    let mut bob = bob.spawn();
+
+    bob.connect(&alice).converge([&alice]);
+
+    test(
+        "examples/rad-clone.md",
+        &working.join("bob"),
+        Some(&bob.home),
+        [],
+    )
+    .unwrap();
+    formula(&environment.tmp(), "examples/git/git-tag.md")
+        .unwrap()
+        .home(
+            "alice",
+            working.join("alice"),
+            [("RAD_HOME", alice.home.path().display())],
+        )
+        .home(
+            "bob",
+            working.join("bob"),
+            [("RAD_HOME", bob.home.path().display())],
+        )
+        .run()
+        .unwrap();
+}
+
 #[test]
 fn rad_workflow() {
     let mut environment = Environment::new();

radicle-fetch/src/git/repository.rs

@@ -1,7 +1,7 @@
 pub mod error;
 
 use either::Either;
-use radicle::git::{Namespaced, Oid, Qualified};
+use radicle::git::{self, Namespaced, Oid, Qualified};
 use radicle::storage::git::Repository;
 
 use super::refs::{Applied, Policy, RefUpdate, Update};
@@ -38,10 +38,29 @@ pub fn contains(repo: &Repository, oid: Oid) -> Result<bool, error::Contains> {
         .map_err(error::Contains)
 }
 
-pub fn ancestry(repo: &Repository, old: Oid, new: Oid) -> Result<Ancestry, error::Ancestry> {
-    if !contains(repo, old)? || !contains(repo, new)? {
-        return Err(error::Ancestry::Missing { a: old, b: new });
+/// Find the object identified by `oid` and peel it to its associated
+/// commit `Oid`.
+///
+/// # Errors
+///
+/// - The object was not found
+/// - The object does not peel to a commit
+/// - Attempting to find the object fails
+fn find_and_peel(repo: &Repository, oid: Oid) -> Result<Oid, error::Ancestry> {
+    match repo.backend.find_object(*oid, None) {
+        Ok(object) => Ok(object
+            .peel(git::raw::ObjectType::Commit)
+            .map_err(|err| error::Ancestry::Peel { oid, err })?
+            .id()
+            .into()),
+        Err(e) if git::is_not_found_err(&e) => Err(error::Ancestry::Missing { oid }),
+        Err(err) => Err(error::Ancestry::Object { oid, err }),
     }
+}
+
+pub fn ancestry(repo: &Repository, old: Oid, new: Oid) -> Result<Ancestry, error::Ancestry> {
+    let old = find_and_peel(repo, old)?;
+    let new = find_and_peel(repo, new)?;
 
     if old == new {
         return Ok(Ancestry::Equal);
@@ -49,7 +68,7 @@ pub fn ancestry(repo: &Repository, old: Oid, new: Oid) -> Result<Ancestry, error
 
     let (ahead, behind) = repo
         .backend
-        .graph_ahead_behind(new.into(), old.into())
+        .graph_ahead_behind(*new, *old)
         .map_err(|err| error::Ancestry::Check { old, new, err })?;
 
     if ahead > 0 && behind == 0 {

radicle-fetch/src/git/repository/error.rs

@@ -7,17 +7,27 @@ pub struct Contains(#[source] pub raw::Error);
 
 #[derive(Debug, Error)]
 pub enum Ancestry {
-    #[error("missing one of {a} or {b} while checking ancestry")]
-    Missing { a: Oid, b: Oid },
-    #[error(transparent)]
-    Contains(#[from] Contains),
-    #[error("failed to check ancestry for {old} and {new}")]
+    #[error("missing {oid} while checking ancestry")]
+    Missing { oid: Oid },
+    #[error("failed to check ancestry for {old} and {new}: {err}")]
     Check {
         old: Oid,
         new: Oid,
         #[source]
         err: raw::Error,
     },
+    #[error("failed to peel object to commit {oid}: {err}")]
+    Peel {
+        oid: Oid,
+        #[source]
+        err: raw::Error,
+    },
+    #[error("failed to find object {oid}: {err}")]
+    Object {
+        oid: Oid,
+        #[source]
+        err: raw::Error,
+    },
 }
 
 #[derive(Debug, Error)]