workspace add/forget: bridge jj workspaces with git worktrees

CHANGELOG.md

@@ -24,6 +24,12 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   jj workspace can have its own Git HEAD. Existing repositories are migrated
   automatically.
 
+* `jj workspace add` supports `--colocate`/`--no-colocate` flags to control
+  whether a Git worktree is created alongside the workspace. The default
+  colocates when the current workspace is colocated and the `git.colocate`
+  config is `true`. `jj workspace forget` removes the corresponding Git
+  worktree when one exists.
+
 ### Fixed bugs
 
 * The default pager flags now include `-K` (`--quit-on-intr`), so pressing

cli/src/commands/workspace/add.rs

@@ -19,6 +19,8 @@ use itertools::Itertools as _;
 use jj_lib::commit::CommitIteratorExt as _;
 use jj_lib::file_util;
 use jj_lib::file_util::IoResultExt as _;
+#[cfg(feature = "git")]
+use jj_lib::git::GitSettings;
 use jj_lib::ref_name::WorkspaceNameBuf;
 use jj_lib::repo::Repo as _;
 use jj_lib::rewrite::merge_commit_trees;
@@ -32,6 +34,8 @@ use crate::command_error::internal_error_with_message;
 use crate::command_error::user_error;
 use crate::description_util::add_trailers;
 use crate::description_util::join_message_paragraphs;
+#[cfg(feature = "git")]
+use crate::git_util::create_git_worktree;
 use crate::ui::Ui;
 
 /// How to handle sparse patterns when creating a new workspace.
@@ -81,6 +85,20 @@ pub struct WorkspaceAddArgs {
     #[arg(long = "message", short, value_name = "MESSAGE")]
     message_paragraphs: Vec<String>,
 
+    /// Create a corresponding Git worktree for this workspace
+    ///
+    /// By default, a Git worktree is created when the current workspace is
+    /// colocated and the [git.colocate config] is `true`.
+    ///
+    /// [git.colocate config]:
+    ///     https://docs.jj-vcs.dev/latest/config/#default-colocation
+    #[arg(long, conflicts_with = "no_colocate")]
+    colocate: bool,
+
+    /// Do not create a Git worktree for this workspace
+    #[arg(long, conflicts_with = "colocate")]
+    no_colocate: bool,
+
     /// How to handle sparse patterns when creating a new workspace.
     #[arg(long, value_enum, default_value_t = SparseInheritance::Copy)]
     sparse_patterns: SparseInheritance,
@@ -114,12 +132,54 @@ pub async fn cmd_workspace_add(
             name = workspace_name.as_symbol()
         )));
     }
-    if !destination_path.exists() {
-        fs::create_dir(&destination_path).context(&destination_path)?;
-    } else if !file_util::is_empty_dir(&destination_path)? {
-        return Err(user_error(
-            "Destination path exists and is not an empty directory",
-        ));
+    #[cfg(feature = "git")]
+    let created_git_worktree = {
+        if (args.colocate || args.no_colocate)
+            && !jj_lib::git::get_git_backend(repo.store()).is_ok()
+        {
+            return Err(user_error(
+                "--colocate/--no-colocate requires a Git backend",
+            ));
+        }
+        let should_colocate = if args.colocate {
+            true
+        } else if args.no_colocate {
+            false
+        } else {
+            old_workspace_command.working_copy_shared_with_git()
+                && old_workspace_command.settings().get_bool("git.colocate")?
+        };
+        if should_colocate {
+            let git_settings = GitSettings::from_settings(old_workspace_command.settings())?;
+            let git_head = repo.view().git_head(old_workspace_command.workspace_name());
+            if git_head.is_absent() {
+                return Err(user_error(
+                    "Cannot create colocated Git worktree because Git HEAD does not point to a \
+                     commit yet. Create a commit first, then retry.",
+                ));
+            }
+            create_git_worktree(
+                ui,
+                &git_settings,
+                old_workspace_command.workspace_root(),
+                &destination_path,
+            )?;
+            true
+        } else {
+            false
+        }
+    };
+    #[cfg(not(feature = "git"))]
+    let created_git_worktree = false;
+
+    if !created_git_worktree {
+        if !destination_path.exists() {
+            fs::create_dir(&destination_path).context(&destination_path)?;
+        } else if !file_util::is_empty_dir(&destination_path)? {
+            return Err(user_error(
+                "Destination path exists and is not an empty directory",
+            ));
+        }
     }
 
     let working_copy_factory = command.get_working_copy_factory()?;

cli/src/commands/workspace/forget.rs

@@ -14,6 +14,8 @@
 
 use clap_complete::ArgValueCandidates;
 use itertools::Itertools as _;
+#[cfg(feature = "git")]
+use jj_lib::git::GitSettings;
 use jj_lib::ref_name::WorkspaceNameBuf;
 use jj_lib::workspace_store::SimpleWorkspaceStore;
 use jj_lib::workspace_store::WorkspaceStore as _;
@@ -22,6 +24,8 @@ use tracing::instrument;
 use crate::cli_util::CommandHelper;
 use crate::command_error::CommandError;
 use crate::complete;
+#[cfg(feature = "git")]
+use crate::git_util::remove_git_worktree;
 use crate::ui::Ui;
 
 /// Stop tracking a workspace's working-copy commit in the repo
@@ -74,6 +78,18 @@ pub async fn cmd_workspace_forget(
 
     let workspace_store = SimpleWorkspaceStore::load(workspace_command.repo_path())?;
 
+    #[cfg(feature = "git")]
+    let workspace_paths = {
+        let repo_path = workspace_command.repo_path();
+        forget_ws
+            .iter()
+            .filter_map(|ws| {
+                let rel_path = workspace_store.get_workspace_path(ws).ok().flatten()?;
+                dunce::canonicalize(repo_path.join(rel_path)).ok()
+            })
+            .collect_vec()
+    };
+
     // bundle every workspace forget into a single transaction, so that e.g.
     // undo correctly restores all of them at once.
     let mut tx = workspace_command.start_transaction();
@@ -94,5 +110,14 @@ pub async fn cmd_workspace_forget(
     };
 
     tx.finish(ui, description).await?;
+
+    #[cfg(feature = "git")]
+    {
+        let git_settings = GitSettings::from_settings(workspace_command.settings())?;
+        for path in &workspace_paths {
+            remove_git_worktree(ui, &git_settings, workspace_command.workspace_root(), path)?;
+        }
+    }
+
     Ok(())
 }

cli/src/git_util.rs

@@ -20,6 +20,7 @@ use std::io::Write as _;
 use std::iter;
 use std::mem;
 use std::path::Path;
+use std::process::Command;
 use std::time::Duration;
 use std::time::Instant;
 
@@ -28,6 +29,8 @@ use crossterm::terminal::Clear;
 use crossterm::terminal::ClearType;
 use indoc::writedoc;
 use itertools::Itertools as _;
+use jj_lib::file_util;
+use jj_lib::file_util::IoResultExt as _;
 use jj_lib::git;
 use jj_lib::git::FailedRefExportReason;
 use jj_lib::git::GitExportStats;
@@ -53,6 +56,7 @@ use crate::cli_util::print_updated_commits;
 use crate::command_error::CommandError;
 use crate::command_error::cli_error;
 use crate::command_error::user_error;
+use crate::command_error::user_error_with_message;
 use crate::formatter::Formatter;
 use crate::formatter::FormatterExt as _;
 use crate::revset_util::parse_remote_auto_track_bookmarks_map;
@@ -565,6 +569,135 @@ pub fn print_push_stats(ui: &Ui, stats: &GitPushStats) -> io::Result<()> {
     Ok(())
 }
 
+pub fn create_git_worktree(
+    ui: &Ui,
+    git_settings: &GitSettings,
+    main_workspace_root: &Path,
+    destination: &Path,
+) -> Result<(), CommandError> {
+    // Use relative paths to match jj's convention for portable repositories.
+    // Silently ignored by git versions that don't support it.
+    let relative_paths_config = ["-c", "worktree.useRelativePaths=true"];
+
+    let dest_exists = destination.exists() && !file_util::is_empty_dir(destination)?;
+    if dest_exists {
+        // `git worktree add` refuses to create a worktree in a non-empty
+        // directory. Work around this by creating in a temporary sibling
+        // directory, moving the .git gitlink, and repairing the paths.
+        let tmp =
+            tempfile::TempDir::new_in(destination.parent().unwrap_or(std::path::Path::new(".")))
+                .map_err(|err| {
+                    user_error_with_message(
+                        "Failed to create temporary directory for Git worktree",
+                        err,
+                    )
+                })?;
+        let tmp_path = tmp.keep();
+
+        run_git_worktree_add(
+            git_settings,
+            &relative_paths_config,
+            main_workspace_root,
+            &tmp_path,
+        )?;
+
+        std::fs::rename(tmp_path.join(".git"), destination.join(".git")).context(destination)?;
+        std::fs::remove_dir_all(&tmp_path).ok();
+
+        let output = Command::new(&git_settings.executable_path)
+            .args(relative_paths_config)
+            .args(["worktree", "repair", "--"])
+            .arg(destination)
+            .current_dir(main_workspace_root)
+            .output()
+            .map_err(|err| user_error_with_message("Failed to run `git worktree repair`", err))?;
+        if !output.status.success() {
+            let stderr = String::from_utf8_lossy(&output.stderr);
+            return Err(user_error(format!(
+                "Failed to repair Git worktree paths: {stderr}"
+            )));
+        }
+    } else {
+        run_git_worktree_add(
+            git_settings,
+            &relative_paths_config,
+            main_workspace_root,
+            destination,
+        )?;
+    }
+
+    writeln!(ui.status(), "Created Git worktree for the new workspace.")?;
+    Ok(())
+}
+
+fn run_git_worktree_add(
+    git_settings: &GitSettings,
+    extra_config: &[&str],
+    main_workspace_root: &Path,
+    destination: &Path,
+) -> Result<(), CommandError> {
+    let output = Command::new(&git_settings.executable_path)
+        .args(extra_config)
+        .args(["worktree", "add", "--detach", "--no-checkout", "--"])
+        .arg(destination)
+        .arg("HEAD")
+        .current_dir(main_workspace_root)
+        .output()
+        .map_err(|err| user_error_with_message("Failed to run `git worktree add`", err))?;
+    if !output.status.success() {
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        return Err(user_error(format!(
+            "Failed to create Git worktree: {stderr}"
+        )));
+    }
+    Ok(())
+}
+
+pub fn remove_git_worktree(
+    ui: &Ui,
+    git_settings: &GitSettings,
+    main_workspace_root: &Path,
+    worktree_path: &Path,
+) -> Result<(), CommandError> {
+    let dot_git = worktree_path.join(".git");
+    if !dot_git.is_file() {
+        return Ok(());
+    }
+    // Remove the .git gitlink file, then prune the worktree metadata.
+    // We don't use `git worktree remove` because it deletes the directory
+    // contents, and jj workspace forget should preserve workspace files.
+    std::fs::remove_file(&dot_git).ok();
+
+    let output = Command::new(&git_settings.executable_path)
+        .args(["worktree", "prune"])
+        .current_dir(main_workspace_root)
+        .output();
+    match output {
+        Ok(o) if o.status.success() => {
+            writeln!(
+                ui.status(),
+                r#"Removed Git worktree for "{}"."#,
+                worktree_path.display()
+            )?;
+        }
+        Ok(o) => {
+            let stderr = String::from_utf8_lossy(&o.stderr);
+            writeln!(
+                ui.warning_default(),
+                r#"Failed to prune Git worktree for "{}": {stderr}"#,
+                worktree_path.display()
+            )?;
+        }
+        Err(err) => {
+            writeln!(
+                ui.warning_default(),
+                "Failed to run `git worktree prune`: {err}"
+            )?;
+        }
+    }
+    Ok(())
+}
+
 #[cfg(test)]
 mod tests {
     use std::path::MAIN_SEPARATOR;

cli/tests/cli-reference@.md.snap

@@ -3800,6 +3800,12 @@ By default, the new workspace inherits the sparse patterns of the current worksp
 
    If any revisions are specified, the new workspace will be created, and the new working-copy commit will be created with all these revisions as parents, i.e. the working-copy commit will exist as if you had run `jj new r1 r2 r3 ...`.
 * `-m`, `--message <MESSAGE>` — The change description to use
+* `--colocate` — Create a corresponding Git worktree for this workspace
+
+   By default, a Git worktree is created when the current workspace is colocated and the [git.colocate config] is `true`.
+
+   [git.colocate config]: https://docs.jj-vcs.dev/latest/config/#default-colocation
+* `--no-colocate` — Do not create a Git worktree for this workspace
 * `--sparse-patterns <SPARSE_PATTERNS>` — How to handle sparse patterns when creating a new workspace
 
   Default value: `copy`