workspace: allow extensions to customize the creation of the .jj dire…

…ctory

Some specialized filesystems may need custom behavior here, by synthesizing the directory through another mechanism, or by accepting its prior existence in specific circumstances.

cli/examples/custom-working-copy/main.rs

@@ -34,7 +34,9 @@ use jj_lib::working_copy::{
     CheckoutError, CheckoutStats, LockedWorkingCopy, ResetError, SnapshotError, SnapshotOptions,
     WorkingCopy, WorkingCopyFactory, WorkingCopyStateError,
 };
-use jj_lib::workspace::{default_working_copy_factories, Workspace, WorkspaceInitError};
+use jj_lib::workspace::{
+    create_jj_dir, default_working_copy_factories, Workspace, WorkspaceInitError,
+};
 
 #[derive(clap::Parser, Clone, Debug)]
 enum CustomCommand {
@@ -58,6 +60,7 @@ fn run_custom_command(
             Workspace::init_with_factories(
                 command_helper.settings(),
                 wc_path,
+                create_jj_dir,
                 &backend_initializer,
                 Signer::from_settings(command_helper.settings())
                     .map_err(WorkspaceInitError::SignInit)?,

lib/src/workspace.rs

@@ -87,7 +87,11 @@ pub struct Workspace {
     working_copy: Box<dyn WorkingCopy>,
 }
 
-fn create_jj_dir(workspace_root: &Path) -> Result<PathBuf, WorkspaceInitError> {
+/// Default function to create the .jj directory inside an existing repo
+/// directory.
+///
+/// Custom extensions can override this to do alternative initialization.
+pub fn create_jj_dir(workspace_root: &Path) -> Result<PathBuf, WorkspaceInitError> {
     let jj_dir = workspace_root.join(".jj");
     match std::fs::create_dir(&jj_dir).context(&jj_dir) {
         Ok(()) => Ok(jj_dir),
@@ -230,6 +234,7 @@ impl Workspace {
     pub fn init_with_factories(
         user_settings: &UserSettings,
         workspace_root: &Path,
+        jj_dir_creator: impl FnOnce(&Path) -> Result<PathBuf, WorkspaceInitError>,
         backend_initializer: &BackendInitializer,
         signer: Signer,
         op_store_initializer: &OpStoreInitializer,
@@ -239,7 +244,7 @@ impl Workspace {
         working_copy_factory: &dyn WorkingCopyFactory,
         workspace_id: WorkspaceId,
     ) -> Result<(Self, Arc<ReadonlyRepo>), WorkspaceInitError> {
-        let jj_dir = create_jj_dir(workspace_root)?;
+        let jj_dir = jj_dir_creator(workspace_root)?;
         (|| {
             let repo_dir = jj_dir.join("repo");
             std::fs::create_dir(&repo_dir).context(&repo_dir)?;
@@ -284,6 +289,7 @@ impl Workspace {
         Self::init_with_factories(
             user_settings,
             workspace_root,
+            create_jj_dir,
             backend_initializer,
             signer,
             ReadonlyRepo::default_op_store_initializer(),