hanna/fabrica

feat(git): surface merge/rebase conflict details

c55d70c · hanna committed on 2026-07-25

MergeConflict now carries the conflicting paths (from merge-tree) or the rebase
output, and the PR merge error shows them, so a failed merge/rebase explains
itself instead of a bare "could not be merged cleanly". Add a diverged
non-conflicting merge/squash/rebase test (previously only fast-forward was
covered) confirming all three strategies succeed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Signed by hannaSSH key fingerprint: SHA256:4g9cWhkAAw8gwqhJUcVbSnGEvdGwklW+1Aa/fMUu59k

crates/git/src/lib.rs +4 −3

crates/git/src/merge.rs +65 −3

crates/web/src/pulls.rs +4 −1

data/repos/01/01kyc0j4dzrnx6afv3wwfvxgn4.git/logs/HEAD +1 −0

data/repos/01/01kyc0j4dzrnx6afv3wwfvxgn4.git/logs/refs/heads/main +1 −0

data/repos/01/01kyc0j4dzrnx6afv3wwfvxgn4.git/objects/94/ffb4ef79a86c7e24d038233859149ba61439aa +0 −0

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data/repos/01/01kyc0j4dzrnx6afv3wwfvxgn4.git/refs/heads/main +1 −1

     Merge(String),
     /// A server-side merge could not apply cleanly: the three-way merge or the
-    /// rebase replay hit conflicts.
+    /// rebase replay hit conflicts. The string names the conflicting paths (or
-    #[error("merge has conflicts")]
+    /// the git output) when available.
-    MergeConflict,
+    #[error("merge has conflicts: {0}")]
+    MergeConflict(String),
     /// `git init` (used for SHA-256 repositories) failed.
     #[error("git init failed: {0}")]

         })?;
     match tree_out.status.code() {
         Some(0) => {}
-        Some(1) => return Err(GitError::MergeConflict),
+        Some(1) => {
+            // On a conflict, stdout is the (partial) tree oid followed by the
+            // conflicted-file information; surface that as the detail.
+            let out = String::from_utf8_lossy(&tree_out.stdout);
+            let detail = out.lines().skip(1).collect::<Vec<_>>().join("; ");
+            return Err(GitError::MergeConflict(detail.trim().to_string()));
+        }
         _ => {
             return Err(GitError::Merge(
                 String::from_utf8_lossy(&tree_out.stderr).trim().to_string(),
         source,
     })?;
     if !out.status.success() {
+        // Capture the reason before aborting (git prints it to stdout/stderr).
+        let mut detail = String::from_utf8_lossy(&out.stdout).trim().to_string();
+        let err = String::from_utf8_lossy(&out.stderr);
+        if !err.trim().is_empty() {
+            detail.push_str(err.trim());
+        }
         // Leave no half-applied rebase state in the worktree.
         let _ = identified(req)
             .current_dir(req.workdir)
             .env_remove("GIT_DIR")
             .args(["rebase", "--abort"])
             .status();
-        return Err(GitError::MergeConflict);
+        return Err(GitError::MergeConflict(detail));
+    }
     let tip = identified(req)
 #[cfg(test)]
 mod tests {
-    #![allow(clippy::unwrap_used, clippy::expect_used)]
+    #![allow(clippy::unwrap_used, clippy::expect_used, clippy::panic)]
     use std::path::{Path, PathBuf};
+    }
     #[test]
+    fn merge_and_rebase_diverged_non_conflicting() {
+        if !git_present() {
+            return;
+        }
+        let fx = fixture();
+        let raw = Repository::open_bare(&fx.path).unwrap();
+        // Advance main with a *different* file, so main and feature diverge from
+        // their common base but do not conflict.
+        let base = raw
+            .find_reference("refs/heads/main")
+            .unwrap()
+            .target()
+            .unwrap();
+        commit(
+            &raw,
+            "main",
+            &[base],
+            &[("README.md", "hello\n"), ("main.txt", "m\n")],
+            "advance main",
+,
+        );
+        // analyze must agree it is clean...
+        assert_eq!(
+            analyze("git", &fx.path, fx.home.path(), "main", "feature").unwrap(),
+            Mergeability::Clean,
+        );
+        // ...and each strategy must succeed, not report a phantom conflict.
+        for (strategy, dir) in [
+            (MergeStrategy::Merge, "wt-div-merge"),
+            (MergeStrategy::Squash, "wt-div-squash"),
+            (MergeStrategy::Rebase, "wt-div-rebase"),
+        ] {
+            let wt = fx.path.parent().unwrap().join(dir);
+            let sha = merge(&request(&fx, strategy, &wt))
+                .unwrap_or_else(|e| panic!("{strategy:?} failed: {e:?}"));
+            let raw = Repository::open_bare(&fx.path).unwrap();
+            assert!(
+                raw.find_commit(git2::Oid::from_str(&sha).unwrap())
+                    .unwrap()
+                    .tree()
+                    .unwrap()
+                    .get_name("feature.txt")
+                    .is_some(),
+                "{strategy:?}: merged tree keeps feature.txt"
+            );
+        }
+    }
+    #[test]
     fn analyze_reports_clean_and_already_merged() {
         if !git_present() {
             return;

     .map_err(AppError::internal)?;
     sha.map_err(|e| match e {
-        git::GitError::MergeConflict => {
+        git::GitError::MergeConflict(detail) if detail.is_empty() => {
             AppError::BadRequest("The branch could not be merged cleanly.".to_string())
+        }
+        git::GitError::MergeConflict(detail) => {
+            AppError::BadRequest(format!("The branch could not be merged cleanly: {detail}"))
+        }
         other => AppError::from(other),
     })
+}

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 f09bd3e7f54bc32b967fdffb126b533e1a487f4d 1570ae1be5f4b82bf24e1115681290e6d68808bf Hanna <me@hanna.lol> 1785020132 -0400
+ae1be5f4b82bf24e1115681290e6d68808bf 94ffb4ef79a86c7e24d038233859149ba61439aa Hanna <me@hanna.lol> 1785020888 -0400

 0000000000000000000000000000000000000000 f09bd3e7f54bc32b967fdffb126b533e1a487f4d hanna <me@hanna.lol> 1784962339 -0400	push
 f09bd3e7f54bc32b967fdffb126b533e1a487f4d 1570ae1be5f4b82bf24e1115681290e6d68808bf Hanna <me@hanna.lol> 1785020132 -0400
+ae1be5f4b82bf24e1115681290e6d68808bf 94ffb4ef79a86c7e24d038233859149ba61439aa Hanna <me@hanna.lol> 1785020888 -0400

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1	1570ae1be5f4b82bf24e1115681290e6d68808bf	1	94ffb4ef79a86c7e24d038233859149ba61439aa