From baa7c85ff3db2366d67ac875fca48ad6dcabf212 Mon Sep 17 00:00:00 2001
From: Joel Klinghed <the_jk@spawned.biz>
Date: Mon, 9 Jun 2025 23:03:30 +0200
Subject: git: Make fetch return the new head for the fetched branch

---
 server/common/src/git.rs   | 39 +++++++++++++++++++++++++++++++++++----
 server/common/src/tests.rs | 10 +++++-----
 server/src/git_root.rs     |  2 +-
 3 files changed, 41 insertions(+), 10 deletions(-)

(limited to 'server')

diff --git a/server/common/src/git.rs b/server/common/src/git.rs
index 053ff3f..8fe7863 100644
--- a/server/common/src/git.rs
+++ b/server/common/src/git.rs
@@ -122,6 +122,22 @@ fn parse_tree_entries(output: String) -> Vec<TreeEntry> {
     ret
 }
 
+fn branch_eq(a: impl AsRef<str>, b: impl AsRef<str>) -> bool {
+    let a = a.as_ref();
+    let b = b.as_ref();
+    if a.starts_with("refs/heads/") {
+        if b.starts_with("refs/heads/") {
+            return a[11..] == b[11..];
+        }
+        return a == format!("refs/heads/{b}");
+    } else {
+        if b.starts_with("refs/heads/") {
+            return format!("refs/heads/{a}") == b;
+        }
+        return a == b;
+    }
+}
+
 impl RepoData {
     fn new() -> Self {
         Self {
@@ -130,7 +146,7 @@ impl RepoData {
         }
     }
 
-    async fn fetch(&self, repo: &Repository, branch: String) -> Result<(), Error> {
+    async fn fetch(&self, repo: &Repository, branch: String) -> Result<String, Error> {
         if repo.remote.is_none() {
             return Err(Error::new("No remote set"));
         }
@@ -149,9 +165,24 @@ impl RepoData {
         // <+ force update><remote branch>:<local branch>
         cmd.arg(format!("+{branch}:{branch}"));
 
-        self.output(&mut cmd).await?;
+        let output = self.output(&mut cmd).await?;
+
+        // git fetch porcelain format:
+        // <flag> <old-object-id> <new-object-id> <local-reference>
+        for line in output.lines() {
+            let mut parts = line.split(' ');
+            parts.next(); // flag
+            parts.next(); // old-object-id
+            if let Some(new_object_id) = parts.next() {
+                let local_reference = parts.collect::<Vec<&str>>().join(" ");
+                if branch_eq(local_reference, &branch) {
+                    return Ok(new_object_id.to_string());
+                }
+            }
+        }
 
-        Ok(())
+        assert!(false);
+        Err(Error::new("Fetch succeeded but branch not found"))
     }
 
     async fn init(&mut self, repo: &Repository) -> Result<(), Error> {
@@ -590,7 +621,7 @@ impl Repository {
         Ok(())
     }
 
-    pub async fn fetch(&self, branch: impl Into<String>) -> Result<(), Error> {
+    pub async fn fetch(&self, branch: impl Into<String>) -> Result<String, Error> {
         let branch = branch.into();
         let data = self.lock.read().await;
 
diff --git a/server/common/src/tests.rs b/server/common/src/tests.rs
index 34cc315..c8553f7 100644
--- a/server/common/src/tests.rs
+++ b/server/common/src/tests.rs
@@ -272,15 +272,15 @@ async fn git_fetch(bare: bool) -> git::Repository {
             repo.fetch("branch"),
             repo.fetch("other"),
         );
-        main.unwrap();
-        branch.unwrap();
-        other.unwrap();
+        assert_eq!(main.unwrap(), "d7c502b9c6b833060576a0c4da0287933d603011");
+        assert_eq!(branch.unwrap(), "2d05d489d42d4f36dd0ebf52502f243991e010eb");
+        assert_eq!(other.unwrap(), "2cecdec660a30bf3964cee645d9cee03640ef8dc");
     } else {
         // Not bare repo will complain when you try to fetch into the currently checked
         // out branch. So just try fetching other branches.
         let (branch, other) = tokio::join!(repo.fetch("branch"), repo.fetch("other"));
-        branch.unwrap();
-        other.unwrap();
+        assert_eq!(branch.unwrap(), "2d05d489d42d4f36dd0ebf52502f243991e010eb");
+        assert_eq!(other.unwrap(), "2cecdec660a30bf3964cee645d9cee03640ef8dc");
     }
     repo
 }
diff --git a/server/src/git_root.rs b/server/src/git_root.rs
index 01cc2b5..71ad96f 100644
--- a/server/src/git_root.rs
+++ b/server/src/git_root.rs
@@ -535,7 +535,7 @@ async fn setup_project_root(
         let bg_project_id = project_id.clone();
         tokio::spawn(async move {
             match bg_repo.fetch(&main_branch).await {
-                Ok(()) => {}
+                Ok(_) => {}
                 Err(e) => {
                     error!("{bg_project_id}: fetch {main_branch} returned {e:?}");
                 }
-- 
cgit v1.2.3-70-g09d2