From 1eb913d444b208ef8f09c9cc6a274b86944eb28e Mon Sep 17 00:00:00 2001
From: Martin von Zweigbergk <martinvonz@google.com>
Date: Thu, 17 Feb 2022 20:06:44 -0800
Subject: [PATCH] cli: when setting git HEAD in collocated repo, also update
 own record

When running in a working copy collocated with git's, we export the
working copy's commit's parent to git after every command. However, we
forgot to update our own record of git's HEAD. That means that on
subsequent imports from git, it'll look like the user had updated HEAD
using a git command. When we detect that, we trust that the user had
taken care of the changes in the working copy and we simply abandon
our old working copy commit. That led to the bug reported in $54,
where the second commit of a `jj split` got lost.

The fix is to also update our record of where git's HEAD is when we
tell git to update it.

Closes #54.
---
 src/commands.rs | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/src/commands.rs b/src/commands.rs
index fb1c855ae..69bad3e92 100644
--- a/src/commands.rs
+++ b/src/commands.rs
@@ -46,7 +46,7 @@ use jujutsu_lib::op_heads_store::OpHeadsStore;
 use jujutsu_lib::op_store::{OpStore, OpStoreError, OperationId, RefTarget, WorkspaceId};
 use jujutsu_lib::operation::Operation;
 use jujutsu_lib::refs::{classify_branch_push_action, BranchPushAction};
-use jujutsu_lib::repo::{ReadonlyRepo, RepoRef};
+use jujutsu_lib::repo::{MutableRepo, ReadonlyRepo, RepoRef};
 use jujutsu_lib::repo_path::RepoPath;
 use jujutsu_lib::revset::{RevsetError, RevsetExpression, RevsetParseError};
 use jujutsu_lib::revset_graph_iterator::RevsetGraphEdgeType;
@@ -315,25 +315,24 @@ impl WorkspaceCommandHelper {
         Ok(())
     }
 
-    fn export_git_refs_and_head(&mut self) -> Result<(), CommandError> {
-        let repo = self.repo();
-        let git_repo = repo.store().git_repo().unwrap();
+    fn export_head_to_git(&self, mut_repo: &mut MutableRepo) -> Result<(), CommandError> {
+        let git_repo = mut_repo.store().git_repo().unwrap();
         let current_git_head_ref = git_repo.find_reference("HEAD").unwrap();
         let current_git_commit_id = current_git_head_ref
             .peel_to_commit()
             .ok()
             .map(|commit| commit.id());
-        git::export_refs(repo, &git_repo)?;
-        if let Some(checkout_id) = repo.view().get_checkout(&self.workspace_id()) {
+        if let Some(checkout_id) = mut_repo.view().get_checkout(&self.workspace_id()) {
             let first_parent_id =
-                repo.index().entry_by_id(checkout_id).unwrap().parents()[0].commit_id();
-            if first_parent_id != *repo.store().root_commit_id() {
+                mut_repo.index().entry_by_id(checkout_id).unwrap().parents()[0].commit_id();
+            if first_parent_id != *mut_repo.store().root_commit_id() {
                 if let Some(current_git_commit_id) = current_git_commit_id {
                     git_repo.set_head_detached(current_git_commit_id)?;
                 }
                 let new_git_commit_id = Oid::from_bytes(first_parent_id.as_bytes()).unwrap();
                 let new_git_commit = git_repo.find_commit(new_git_commit_id)?;
                 git_repo.reset(new_git_commit.as_object(), git2::ResetType::Mixed, None)?;
+                mut_repo.set_git_head(first_parent_id);
             }
         } else {
             // The workspace was removed (maybe the user undid the
@@ -627,6 +626,9 @@ impl WorkspaceCommandHelper {
                 writeln!(ui, "Rebased {} descendant commits", num_rebased)?;
             }
         }
+        if self.working_copy_shared_with_git {
+            self.export_head_to_git(mut_repo)?;
+        }
         let maybe_old_tree_id = tx
             .base_repo()
             .view()
@@ -652,7 +654,8 @@ impl WorkspaceCommandHelper {
             }
         }
         if self.working_copy_shared_with_git {
-            self.export_git_refs_and_head()?;
+            let git_repo = self.repo.store().git_repo().unwrap();
+            git::export_refs(&self.repo, &git_repo)?;
         }
         Ok(())
     }