[F] Fix heuristic

src/git.rs

@@ -109,6 +109,27 @@ impl GitMirror {
         self.run(["fetch", "--prune", &remote.name, &tag_refspec])
     }
 
+    pub fn cached_remote_refs_match(
+        &self,
+        remote: &RemoteSpec,
+        expected: &RemoteRefSnapshot,
+    ) -> Result<bool> {
+        if !self.path.exists() || self.dry_run {
+            return Ok(false);
+        }
+        let branches = self.remote_branches(&remote.name)?;
+        let tags = self.remote_tags(&remote.name)?;
+        let mut refs = Vec::with_capacity(branches.len() + tags.len());
+        for (branch, sha) in branches {
+            refs.push(format!("{sha}\trefs/heads/{branch}"));
+        }
+        for (tag, sha) in tags {
+            refs.push(format!("{sha}\trefs/tags/{tag}"));
+        }
+        let snapshot = snapshot_from_refs(refs);
+        Ok(&snapshot == expected)
+    }
+
     pub fn branch_decisions(
         &self,
         remotes: &[RemoteSpec],
@@ -432,18 +453,23 @@ pub fn ls_remote_refs(remote: &RemoteSpec, redactor: &Redactor) -> Result<Remote
         return Err(GitCommandError::new("git ls-remote", stdout, stderr).into());
     }
 
-    let mut refs = String::from_utf8_lossy(&output.stdout)
+    let refs = String::from_utf8_lossy(&output.stdout)
         .lines()
         .map(str::trim)
         .filter(|line| !line.is_empty())
         .map(ToOwned::to_owned)
         .collect::<Vec<_>>();
+
+    Ok(snapshot_from_refs(refs))
+}
+
+fn snapshot_from_refs(mut refs: Vec<String>) -> RemoteRefSnapshot {
     refs.sort();
 
-    Ok(RemoteRefSnapshot {
+    RemoteRefSnapshot {
         hash: stable_ref_hash(&refs),
         refs: refs.len(),
-    })
+    }
 }
 
 fn stable_ref_hash(refs: &[String]) -> String {
@@ -698,6 +724,35 @@ mod tests {
         assert!(main.target_remotes.is_empty());
     }
 
+    #[test]
+    fn cached_remote_refs_match_ls_remote_snapshot_after_fetch() {
+        let fixture = GitFixture::new();
+        fixture.commit("base", "base", 1_700_000_000);
+        fixture.tag("v1");
+        fixture.push_head(&fixture.remote_a, "main");
+        fixture.push_tag(&fixture.remote_a, "v1");
+
+        let mirror = fixture.mirror();
+        let remote = fixture.remotes().remove(0);
+        assert!(
+            !mirror
+                .cached_remote_refs_match(
+                    &remote,
+                    &ls_remote_refs(&remote, &Redactor::new(Vec::new())).unwrap(),
+                )
+                .unwrap()
+        );
+
+        mirror.fetch_remote(&remote).unwrap();
+        let snapshot = ls_remote_refs(&remote, &Redactor::new(Vec::new())).unwrap();
+        assert!(mirror.cached_remote_refs_match(&remote, &snapshot).unwrap());
+
+        fixture.commit("newer", "newer", 1_700_000_100);
+        fixture.push_head(&fixture.remote_a, "main");
+        let changed = ls_remote_refs(&remote, &Redactor::new(Vec::new())).unwrap();
+        assert!(!mirror.cached_remote_refs_match(&remote, &changed).unwrap());
+    }
+
     #[test]
     fn branch_decisions_report_divergent_tips_without_force() {
         let fixture = GitFixture::new();

src/sync.rs

@@ -230,6 +230,15 @@ impl From<RemoteRefSnapshot> for RemoteRefState {
     }
 }
 
+impl From<&RemoteRefState> for RemoteRefSnapshot {
+    fn from(value: &RemoteRefState) -> Self {
+        Self {
+            hash: value.hash.clone(),
+            refs: value.refs,
+        }
+    }
+}
+
 #[derive(Clone, Debug, Default, Deserialize, Serialize)]
 struct RefState {
     #[serde(default)]
@@ -659,8 +668,9 @@ fn sync_repo(
     let Some(initial_ref_state) = check_remote_refs(context, repo_name, &initial_remotes)? else {
         return Ok(RepoSyncOutcome::default());
     };
+    let all_endpoints_present = all_configured_endpoints_present(context.mirror, repos);
     if !context.dry_run
-        && all_configured_endpoints_present(context.mirror, repos)
+        && all_endpoints_present
         && ref_state.repo_matches(&context.mirror.name, repo_name, &initial_ref_state)
     {
         crate::logln!(
@@ -677,6 +687,19 @@ fn sync_repo(
     let mirror_repo = GitMirror::open(path, context.redactor.clone(), context.dry_run)?;
 
     mirror_repo.configure_remotes(&initial_remotes)?;
+    if !context.dry_run
+        && all_endpoints_present
+        && cached_refs_match(&mirror_repo, &initial_remotes, &initial_ref_state)?
+    {
+        crate::logln!(
+            "  {} refs unchanged from local mirror cache",
+            style("up-to-date").green().bold()
+        );
+        return Ok(RepoSyncOutcome {
+            ref_update: Some(initial_ref_state),
+        });
+    }
+
     for remote in &initial_remotes {
         if let Err(error) = mirror_repo.fetch_remote(remote) {
             if is_disabled_repository_error(&error) {
@@ -763,6 +786,22 @@ fn all_configured_endpoints_present(mirror: &MirrorConfig, repos: &[EndpointRepo
         .all(|endpoint| present.contains(endpoint))
 }
 
+fn cached_refs_match(
+    mirror_repo: &GitMirror,
+    remotes: &[RemoteSpec],
+    expected_refs: &BTreeMap<String, RemoteRefState>,
+) -> Result<bool> {
+    for remote in remotes {
+        let Some(expected) = expected_refs.get(&remote.name) else {
+            return Ok(false);
+        };
+        if !mirror_repo.cached_remote_refs_match(remote, &RemoteRefSnapshot::from(expected))? {
+            return Ok(false);
+        }
+    }
+    Ok(true)
+}
+
 fn check_remote_refs(
     context: &RepoSyncContext<'_>,
     repo_name: &str,