POC for GitBackend opening worktrees

cli/examples/custom-backend/main.rs

@@ -106,7 +106,8 @@ impl JitBackend {
     }
 
     fn load(settings: &UserSettings, store_path: &Path) -> Result<Self, BackendLoadError> {
-        let inner = GitBackend::load(settings, store_path)?;
+        let workspace_root = None;
+        let inner = GitBackend::load(settings, store_path, workspace_root)?;
         Ok(JitBackend { inner })
     }
 }

cli/src/cli_util.rs

@@ -386,6 +386,14 @@ impl CommandHelper {
         WorkspaceCommandHelper::new(ui, workspace, repo, env, self.is_at_head_operation())
     }
 
+    pub fn get_store_factories(&self) -> &StoreFactories {
+        &self.data.store_factories
+    }
+
+    pub fn get_working_copy_factories(&self) -> &WorkingCopyFactories {
+        &self.data.working_copy_factories
+    }
+
     pub fn get_working_copy_factory(&self) -> Result<&dyn WorkingCopyFactory, CommandError> {
         let loader = self.workspace_loader()?;
 
@@ -855,7 +863,7 @@ impl WorkspaceCommandHelper {
         let op_summary_template_text = settings.config().get_string("templates.op_summary")?;
         let may_update_working_copy =
             loaded_at_head && !env.command.global_args().ignore_working_copy;
-        let working_copy_shared_with_git = is_colocated_git_workspace(&workspace, &repo);
+        let working_copy_shared_with_git = is_colocated_git_workspace(Some(ui), &repo);
         let helper = Self {
             workspace,
             user_repo: ReadonlyUserRepo::new(repo),
@@ -898,7 +906,7 @@ impl WorkspaceCommandHelper {
     }
 
     /// Snapshot the working copy if allowed, and import Git refs if the working
-    /// copy is collocated with Git.
+    /// copy is colocated with Git.
     #[instrument(skip_all)]
     pub fn maybe_snapshot(&mut self, ui: &Ui) -> Result<(), CommandError> {
         if self.may_update_working_copy {
@@ -1074,6 +1082,18 @@ impl WorkspaceCommandHelper {
         self.working_copy_shared_with_git
     }
 
+    pub fn open_colocated_git_repo_git2(&self) -> Result<Option<git2::Repository>, git2::Error> {
+        if self.working_copy_shared_with_git() {
+            git2::Repository::open(self.workspace_root()).map(Some)
+        } else {
+            Ok(None)
+        }
+    }
+
+    pub fn git_backend_repo(&self) -> Option<gix::Repository> {
+        self.git_backend().map(|backend| backend.git_repo())
+    }
+
     pub fn format_file_path(&self, file: &RepoPath) -> String {
         self.path_converter().format_file_path(file)
     }
@@ -1748,8 +1768,7 @@ See https://martinvonz.github.io/jj/latest/working-copy/#stale-working-copy \
             .map(|commit_id| tx.repo().store().get_commit(commit_id))
             .transpose()?;
 
-        if self.working_copy_shared_with_git {
-            let git_repo = self.git_backend().unwrap().open_git_repo()?;
+        if let Some(git_repo) = self.open_colocated_git_repo_git2()? {
             if let Some(wc_commit) = &maybe_new_wc_commit {
                 git::reset_head(tx.repo_mut(), &git_repo, wc_commit)?;
             }

cli/src/command_error.rs

@@ -304,6 +304,7 @@ impl From<WorkspaceInitError> for CommandError {
             }
             WorkspaceInitError::SignInit(err @ SignInitError::UnknownBackend(_)) => user_error(err),
             WorkspaceInitError::SignInit(err) => internal_error(err),
+            WorkspaceInitError::Internal(err) => internal_error(err),
         }
     }
 }

cli/src/commands/git/clone.rs

@@ -35,7 +35,7 @@ use crate::commands::git::map_git_error;
 use crate::commands::git::maybe_add_gitignore;
 use crate::config::write_config_value_to_file;
 use crate::config::ConfigNamePathBuf;
-use crate::git_util::get_git_repo;
+use crate::git_util::get_git_backend_repo;
 use crate::git_util::print_git_import_stats;
 use crate::git_util::with_remote_git_callbacks;
 use crate::ui::Ui;
@@ -204,7 +204,7 @@ fn do_git_clone(
     } else {
         Workspace::init_internal_git(command.settings(), wc_path)?
     };
-    let git_repo = get_git_repo(repo.store())?;
+    let git_repo = get_git_backend_repo(repo.store())?;
     writeln!(
         ui.status(),
         r#"Fetching into new repo in "{}""#,

cli/src/commands/git/fetch.rs

@@ -27,7 +27,7 @@ use crate::command_error::user_error_with_hint;
 use crate::command_error::CommandError;
 use crate::commands::git::get_single_remote;
 use crate::commands::git::map_git_error;
-use crate::git_util::get_git_repo;
+use crate::git_util::get_git_backend_repo;
 use crate::git_util::print_git_import_stats;
 use crate::git_util::with_remote_git_callbacks;
 use crate::ui::Ui;
@@ -60,7 +60,7 @@ pub fn cmd_git_fetch(
     args: &GitFetchArgs,
 ) -> Result<(), CommandError> {
     let mut workspace_command = command.workspace_helper(ui)?;
-    let git_repo = get_git_repo(workspace_command.repo().store())?;
+    let git_repo = get_git_backend_repo(workspace_command.repo().store())?;
     let remotes = if args.all_remotes {
         get_all_remotes(&git_repo)?
     } else if args.remotes.is_empty() {

cli/src/commands/git/init.rs

@@ -36,7 +36,7 @@ use crate::command_error::CommandError;
 use crate::commands::git::maybe_add_gitignore;
 use crate::config::write_config_value_to_file;
 use crate::config::ConfigNamePathBuf;
-use crate::git_util::get_git_repo;
+use crate::git_util::get_git_backend_repo;
 use crate::git_util::is_colocated_git_workspace;
 use crate::git_util::print_failed_git_export;
 use crate::git_util::print_git_import_stats;
@@ -167,7 +167,9 @@ pub fn do_init(
                 Workspace::init_external_git(command.settings(), workspace_root, git_repo_path)?;
             // Import refs first so all the reachable commits are indexed in
             // chronological order.
-            let colocated = is_colocated_git_workspace(&workspace, &repo);
+            // No UI, because we're about to call this function again in the workspace
+            // command helper, and warnings can be shown then.
+            let colocated = is_colocated_git_workspace(None, &repo);
             let repo = init_git_refs(ui, command, repo, colocated)?;
             let mut workspace_command = command.for_workable_repo(ui, workspace, repo)?;
             maybe_add_gitignore(&workspace_command)?;
@@ -237,7 +239,7 @@ pub fn maybe_set_repository_level_trunk_alias(
     ui: &Ui,
     workspace_command: &WorkspaceCommandHelper,
 ) -> Result<(), CommandError> {
-    let git_repo = get_git_repo(workspace_command.repo().store())?;
+    let git_repo = get_git_backend_repo(workspace_command.repo().store())?;
     if let Ok(reference) = git_repo.find_reference("refs/remotes/origin/HEAD") {
         if let Some(reference_name) = reference.symbolic_target() {
             if let Some(RefName::RemoteBranch {

cli/src/commands/git/push.rs

@@ -48,7 +48,7 @@ use crate::command_error::CommandError;
 use crate::commands::git::get_single_remote;
 use crate::commands::git::map_git_error;
 use crate::formatter::Formatter;
-use crate::git_util::get_git_repo;
+use crate::git_util::get_git_backend_repo;
 use crate::git_util::with_remote_git_callbacks;
 use crate::git_util::GitSidebandProgressMessageWriter;
 use crate::ui::Ui;
@@ -143,7 +143,7 @@ pub fn cmd_git_push(
     args: &GitPushArgs,
 ) -> Result<(), CommandError> {
     let mut workspace_command = command.workspace_helper(ui)?;
-    let git_repo = get_git_repo(workspace_command.repo().store())?;
+    let git_repo = get_git_backend_repo(workspace_command.repo().store())?;
 
     let remote = if let Some(name) = &args.remote {
         name.clone()

cli/src/commands/git/remote/add.rs

@@ -17,7 +17,7 @@ use jj_lib::repo::Repo;
 
 use crate::cli_util::CommandHelper;
 use crate::command_error::CommandError;
-use crate::git_util::get_git_repo;
+use crate::git_util::get_git_backend_repo;
 use crate::ui::Ui;
 
 /// Add a Git remote
@@ -36,7 +36,7 @@ pub fn cmd_git_remote_add(
 ) -> Result<(), CommandError> {
     let workspace_command = command.workspace_helper(ui)?;
     let repo = workspace_command.repo();
-    let git_repo = get_git_repo(repo.store())?;
+    let git_repo = get_git_backend_repo(repo.store())?;
     git::add_remote(&git_repo, &args.remote, &args.url)?;
     Ok(())
 }

cli/src/commands/git/remote/list.rs

@@ -18,7 +18,7 @@ use jj_lib::repo::Repo;
 
 use crate::cli_util::CommandHelper;
 use crate::command_error::CommandError;
-use crate::git_util::get_git_repo;
+use crate::git_util::get_git_backend_repo;
 use crate::ui::Ui;
 
 /// List Git remotes
@@ -32,7 +32,7 @@ pub fn cmd_git_remote_list(
 ) -> Result<(), CommandError> {
     let workspace_command = command.workspace_helper(ui)?;
     let repo = workspace_command.repo();
-    let git_repo = get_git_repo(repo.store())?;
+    let git_repo = get_git_backend_repo(repo.store())?;
     for remote_name in git_repo.remotes()?.iter().flatten() {
         let remote = git_repo.find_remote(remote_name)?;
         writeln!(

cli/src/commands/git/remote/remove.rs

@@ -17,7 +17,7 @@ use jj_lib::repo::Repo;
 
 use crate::cli_util::CommandHelper;
 use crate::command_error::CommandError;
-use crate::git_util::get_git_repo;
+use crate::git_util::get_git_backend_repo;
 use crate::ui::Ui;
 
 /// Remove a Git remote and forget its bookmarks
@@ -34,7 +34,7 @@ pub fn cmd_git_remote_remove(
 ) -> Result<(), CommandError> {
     let mut workspace_command = command.workspace_helper(ui)?;
     let repo = workspace_command.repo();
-    let git_repo = get_git_repo(repo.store())?;
+    let git_repo = get_git_backend_repo(repo.store())?;
     let mut tx = workspace_command.start_transaction();
     git::remove_remote(tx.repo_mut(), &git_repo, &args.remote)?;
     if tx.repo().has_changes() {

cli/src/commands/git/remote/rename.rs

@@ -17,7 +17,7 @@ use jj_lib::repo::Repo;
 
 use crate::cli_util::CommandHelper;
 use crate::command_error::CommandError;
-use crate::git_util::get_git_repo;
+use crate::git_util::get_git_backend_repo;
 use crate::ui::Ui;
 
 /// Rename a Git remote
@@ -36,7 +36,7 @@ pub fn cmd_git_remote_rename(
 ) -> Result<(), CommandError> {
     let mut workspace_command = command.workspace_helper(ui)?;
     let repo = workspace_command.repo();
-    let git_repo = get_git_repo(repo.store())?;
+    let git_repo = get_git_backend_repo(repo.store())?;
     let mut tx = workspace_command.start_transaction();
     git::rename_remote(tx.repo_mut(), &git_repo, &args.old, &args.new)?;
     if tx.repo().has_changes() {

cli/src/commands/git/remote/set_url.rs

@@ -17,7 +17,7 @@ use jj_lib::repo::Repo;
 
 use crate::cli_util::CommandHelper;
 use crate::command_error::CommandError;
-use crate::git_util::get_git_repo;
+use crate::git_util::get_git_backend_repo;
 use crate::ui::Ui;
 
 /// Set the URL of a Git remote
@@ -36,7 +36,7 @@ pub fn cmd_git_remote_set_url(
 ) -> Result<(), CommandError> {
     let workspace_command = command.workspace_helper(ui)?;
     let repo = workspace_command.repo();
-    let git_repo = get_git_repo(repo.store())?;
+    let git_repo = get_git_backend_repo(repo.store())?;
     git::set_remote_url(&git_repo, &args.remote, &args.url)?;
     Ok(())
 }

cli/src/commands/workspace/add.rs

@@ -114,8 +114,10 @@ pub fn cmd_workspace_add(
         repo_path,
         repo,
         working_copy_factory,
+        command.get_store_factories(),
         workspace_id,
     )?;
+
     writeln!(
         ui.status(),
         "Created workspace in \"{}\"",

cli/src/git_util.rs

@@ -35,7 +35,6 @@ use jj_lib::op_store::RemoteRef;
 use jj_lib::repo::ReadonlyRepo;
 use jj_lib::repo::Repo;
 use jj_lib::store::Store;
-use jj_lib::workspace::Workspace;
 use unicode_width::UnicodeWidthStr;
 
 use crate::command_error::user_error;
@@ -44,29 +43,36 @@ use crate::formatter::Formatter;
 use crate::progress::Progress;
 use crate::ui::Ui;
 
-pub fn get_git_repo(store: &Store) -> Result<git2::Repository, CommandError> {
+/// This opens a [git2::Repository] for the underlying [GitBackend], assuming
+/// this store is git-backed.
+///
+/// If the JJ repo is colocated with the git repo, then this will often not be
+/// what you want, because its HEAD will always be for the default workspace.
+/// Most JJ commands that access the HEAD need the one for the current
+/// workspace.
+///
+/// However, sometimes you don't care. For example, when you run `jj git fetch`.
+pub fn get_git_backend_repo(store: &Store) -> Result<git2::Repository, CommandError> {
     match store.backend_impl().downcast_ref::<GitBackend>() {
         None => Err(user_error("The repo is not backed by a git repo")),
         Some(git_backend) => Ok(git_backend.open_git_repo()?),
     }
 }
 
-pub fn is_colocated_git_workspace(workspace: &Workspace, repo: &ReadonlyRepo) -> bool {
+pub fn is_colocated_git_workspace(ui: Option<&Ui>, repo: &ReadonlyRepo) -> bool {
     let Some(git_backend) = repo.store().backend_impl().downcast_ref::<GitBackend>() else {
         return false;
     };
-    let Some(git_workdir) = git_backend.git_workdir() else {
-        return false; // Bare repository
-    };
-    if git_workdir == workspace.workspace_root() {
-        return true;
+
+    let colocation_type = git_backend.colocation_type();
+
+    if let Some((ui, warning)) = ui.zip(colocation_type.warning()) {
+        writeln!(ui.warning_default(), "{warning}").ok();
+        if let Some(hint) = warning.hint() {
+            writeln!(ui.hint_default(), "{hint}").ok();
+        }
     }
-    // Colocated workspace should have ".git" directory, file, or symlink. Compare
-    // its parent as the git_workdir might be resolved from the real ".git" path.
-    let Ok(dot_git_path) = workspace.workspace_root().join(".git").canonicalize() else {
-        return false;
-    };
-    git_workdir.canonicalize().ok().as_deref() == dot_git_path.parent()
+    colocation_type.is_colocated()
 }
 
 fn terminal_get_username(ui: &Ui, url: &str) -> Option<String> {