huskies: merge 675_bug_mergemaster_silently_exits_when_feature_branch_has_zero_commits_ahead_of_master

server/src/agents/merge/squash.rs

@@ -28,6 +28,34 @@ pub(crate) fn run_squash_merge(
         .lock()
         .map_err(|e| format!("Merge lock poisoned: {e}"))?;
 
+    // ── Pre-flight: verify the branch has commits ahead of base ──────────────
+    // A zero-commit branch produces an empty squash and a silent "nothing to
+    // commit" failure.  Catch it early with a grep-able error before any merge
+    // work starts.
+    let base_branch = crate::config::ProjectConfig::load(project_root)
+        .ok()
+        .and_then(|c| c.base_branch.clone())
+        .unwrap_or_else(|| "master".to_string());
+
+    let ahead_out = Command::new("git")
+        .args(["rev-list", "--count", &format!("{base_branch}..{branch}")])
+        .current_dir(project_root)
+        .output()
+        .map_err(|e| format!("Failed to count commits ahead: {e}"))?;
+
+    if ahead_out.status.success() {
+        let ahead: u64 = String::from_utf8_lossy(&ahead_out.stdout)
+            .trim()
+            .parse()
+            .unwrap_or(1); // parse failure → don't false-positive; let merge proceed
+        if ahead == 0 {
+            return Err(format!(
+                "{story_id}: no commits to merge — feature branch '{branch}' \
+                 has 0 commits ahead of '{base_branch}'"
+            ));
+        }
+    }
+
     let mut all_output = String::new();
     let merge_branch = format!("merge-queue/{story_id}");
     let merge_wt_path = project_root.join(".huskies").join("merge_workspace");
@@ -827,16 +855,25 @@ mod tests {
             .output()
             .unwrap();
 
-        let result = run_squash_merge(repo, "feature/story-empty_test", "empty_test").unwrap();
+        let result = run_squash_merge(repo, "feature/story-empty_test", "empty_test");
 
-        // Bug 226: empty diff must NOT be treated as success.
-        assert!(
-            !result.success,
-            "empty diff merge must fail, not silently succeed: {}",
-            result.output
-        );
+        // Bug 226 / 675: a zero-commit branch must not be treated as success.
+        // The pre-flight check (bug 675) returns Err for zero commits ahead;
+        // the older code path returned Ok(SquashMergeResult { success: false }).
+        // Either form is a failure — just not success.
+        match result {
+            Ok(r) => assert!(
+                !r.success,
+                "empty diff merge must fail, not silently succeed: {}",
+                r.output
+            ),
+            Err(e) => assert!(
+                e.contains("no commits to merge") || e.contains("nothing to commit"),
+                "unexpected error: {e}"
+            ),
+        }
 
-        // Cleanup should still happen.
+        // Cleanup should still happen (no workspace was created for the Err path).
         assert!(
             !repo.join(".huskies/merge_workspace").exists(),
             "merge workspace should be cleaned up"