Jj workspace support by martijnberger · Pull Request #1677 · j178/prek

martijnberger · 2026-02-20T10:17:41Z

Motivation

I'm a happy jj (Jujutsu) user and I love prek. I just want the two to work together. Right now, prek fails in jj workspaces because:

Secondary workspaces (created with jj workspace add) have no .git directory, only .jj/. Every git command fails with "fatal: not a git repository".
Even in colocated workspaces, git diff --staged returns empty because jj doesn't use git's staging area. This makes the default prek run mode (which checks staged files) non-functional.

This PR makes prek detect jj workspaces transparently and do the right thing, with no configuration required.

Changes

New: `crates/prek/src/jj.rs`

A new module for all jj-related logic, mirroring git.rs patterns:

IS_JJ_WORKSPACE detects .jj/ by walking up from CWD. detect_jj_git_dir() resolves the backing .git directory from .jj/repo/store/git_target, handling both primary (colocated) and secondary workspaces. setup_git_env_for_jj() sets GIT_DIR and GIT_WORK_TREE env vars early in startup so all git commands work transparently. get_changed_files() uses jj diff --name-only to collect changed files in the working copy.

Modified files

main.rs calls setup_git_env_for_jj() before any GIT_DIR handling.

cli/run/run.rs disables stashing for jj workspaces (stashing, check_configs_staged(), has_unmerged_paths(), and WorkTreeKeeper::clean() are all git-index-specific).

cli/run/filter.rs uses jj::get_changed_files() instead of git::get_staged_files() when in a jj workspace.

git.rs short-circuits is_in_merge_conflict() for jj (jj handles conflicts differently).

Documentation

docs/faq.md new FAQ entry: "Does prek work with Jujutsu (jj)?"

docs/quickstart.md mentions jj working copy alongside git staging area.

docs/workspace.md updated repository boundary description to include .jj.

Test plan

7 new unit tests covering find_jj_dir, colocated workspace resolution, and secondary workspace resolution
All 288 existing unit tests pass
Zero clippy warnings on changed files (including pedantic + nursery lints)
Manual test in a jj colocated workspace with prek run
Manual test in a jj secondary workspace with prek run --all-files
Verify existing git behavior is unaffected (IS_JJ_WORKSPACE = false when no .jj/ exists)

codecov · 2026-02-20T10:19:22Z

Codecov Report

❌ Patch coverage is 75.21127% with 88 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.44%. Comparing base (2c53121) to head (dd4eb52).
⚠️ Report is 30 commits behind head on master.

Files with missing lines	Patch %	Lines
crates/prek/src/jj.rs	66.66%	45 Missing ⚠️
crates/prek/src/repo.rs	78.65%	35 Missing ⚠️
...re_commit_hooks/check_executables_have_shebangs.rs	40.00%	6 Missing ⚠️
crates/prek/src/cli/install.rs	75.00%	1 Missing ⚠️
crates/prek/src/workspace.rs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1677      +/-   ##
==========================================
- Coverage   91.69%   91.44%   -0.26%     
==========================================
  Files          98      100       +2     
  Lines       19999    20288     +289     
==========================================
+ Hits        18339    18552     +213     
- Misses       1660     1736      +76

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

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streadway · 2026-02-20T10:20:48Z

crates/prek/src/cli/run/filter.rs


-    let files = git::get_staged_files(workspace_root).await?;
-    debug!("Staged files: {}", files.len());
+    let files = if *crate::jj::IS_JJ_WORKSPACE {


Rest of the project does not reference crates this way.

as in the crate:: prefix ?

streadway · 2026-02-20T10:24:47Z

crates/prek/src/cli/run/filter.rs

    if all_files {
        let files = git::ls_files(git_root, workspace_root).await?;
        debug!("All files in the workspace: {}", files.len());
        return Ok(files);
    }


jj file list is the jj equiv.

Yeah I think I should take another pass and push this deeper into prek rather then patch the surface

Copilot

Pull request overview

This PR adds support for Jujutsu (jj) workspaces to prek, enabling the tool to work seamlessly with both primary (colocated) and secondary jj workspaces. The implementation detects jj workspaces automatically and adapts prek's behavior to work with jj's different model (no staging area, different conflict handling).

Changes:

Adds new jj.rs module with workspace detection, git directory resolution, and changed files collection
Modifies startup sequence to set GIT_DIR and GIT_WORK_TREE environment variables for jj workspaces
Disables git-index-specific features (stashing, merge conflict detection) when in jj workspaces
Updates documentation to explain jj support

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
crates/prek/src/jj.rs	New module implementing jj workspace detection, git directory resolution for colocated/secondary workspaces, and changed files collection via `jj diff --name-only`
crates/prek/src/main.rs	Calls `setup_git_env_for_jj()` early in startup to configure environment variables before any git commands run
crates/prek/src/cli/run/run.rs	Disables stashing for jj workspaces by adding `!*crate::jj::IS_JJ_WORKSPACE` to the `should_stash` condition
crates/prek/src/cli/run/filter.rs	Uses `jj::get_changed_files()` instead of `git::get_staged_files()` when `IS_JJ_WORKSPACE` is true
crates/prek/src/git.rs	Short-circuits `is_in_merge_conflict()` to return false for jj workspaces since jj handles conflicts differently
docs/faq.md	Adds FAQ entry explaining jj support, automatic detection, and behavioral differences
docs/quickstart.md	Updates `prek run` description to mention jj working copy alongside git staging area
docs/workspace.md	Updates repository boundary description to include `.jj` directory

Copilot · 2026-02-20T10:28:23Z

crates/prek/src/jj.rs

+/// Whether the current working directory is inside a jj workspace.
+pub(crate) static IS_JJ_WORKSPACE: LazyLock<bool> = LazyLock::new(|| {
+    let Ok(cwd) = std::env::current_dir() else {
+        return false;
+    };
+    find_jj_dir(&cwd).is_some()
+});


The IS_JJ_WORKSPACE LazyLock is initialized based on the current working directory at the time it's first accessed. If the working directory changes before this LazyLock is initialized (e.g., via the --cd option), the detection may be incorrect. However, looking at main.rs, setup_git_env_for_jj() is called before the --cd option is processed (line 207), so accessing IS_JJ_WORKSPACE later will use the original cwd. This is correct but fragile - consider documenting this dependency or restructuring to make it more explicit.

Copilot · 2026-02-20T10:28:23Z

crates/prek/src/jj.rs

+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn find_jj_dir_returns_none_for_non_jj_directory() {
+        let dir = tempfile::tempdir().unwrap();
+        assert!(find_jj_dir(dir.path()).is_none());
+    }
+
+    #[test]
+    fn find_jj_dir_finds_jj_in_current_directory() {
+        let dir = tempfile::tempdir().unwrap();
+        std::fs::create_dir(dir.path().join(".jj")).unwrap();
+        let result = find_jj_dir(dir.path());
+        assert_eq!(result, Some(dir.path().join(".jj")));
+    }
+
+    #[test]
+    fn find_jj_dir_finds_jj_in_parent_directory() {
+        let dir = tempfile::tempdir().unwrap();
+        std::fs::create_dir(dir.path().join(".jj")).unwrap();
+        let child = dir.path().join("subdir");
+        std::fs::create_dir(&child).unwrap();
+        let result = find_jj_dir(&child);
+        assert_eq!(result, Some(dir.path().join(".jj")));
+    }
+
+    #[test]
+    fn detect_jj_git_dir_returns_none_without_jj_workspace() {
+        let dir = tempfile::tempdir().unwrap();
+        // No .jj dir at all — detection should return None.
+        // We can't easily test this without changing CWD, so just verify
+        // the helper function returns None.
+        assert!(find_jj_dir(dir.path()).is_none());
+    }
+
+    #[test]
+    fn detect_jj_git_dir_returns_none_without_git_target() {
+        let dir = tempfile::tempdir().unwrap();
+        let jj_dir = dir.path().join(".jj");
+        let repo_dir = jj_dir.join("repo");
+        let store_dir = repo_dir.join("store");
+        std::fs::create_dir_all(&store_dir).unwrap();
+        // No git_target file — should not resolve.
+        // detect_jj_git_dir() reads CWD, so we test the building blocks.
+        assert!(find_jj_dir(dir.path()).is_some());
+        assert!(!store_dir.join("git_target").exists());
+    }
+
+    #[test]
+    fn detect_jj_git_dir_resolves_colocated_workspace() {
+        let dir = tempfile::tempdir().unwrap();
+        let root = dir.path();
+
+        // Set up a colocated jj workspace structure:
+        //   .jj/repo/store/git_target  →  "../../../.git"
+        //   .git/
+        let jj_dir = root.join(".jj");
+        let store_dir = jj_dir.join("repo").join("store");
+        std::fs::create_dir_all(&store_dir).unwrap();
+        std::fs::write(store_dir.join("git_target"), "../../../.git").unwrap();
+        let git_dir = root.join(".git");
+        std::fs::create_dir(&git_dir).unwrap();
+
+        // Since detect_jj_git_dir uses std::env::current_dir, we test the
+        // resolution logic directly.
+        let repo_dir = jj_dir.join("repo");
+        let git_target =
+            std::fs::read_to_string(repo_dir.join("store").join("git_target")).unwrap();
+        let resolved = repo_dir.join("store").join(git_target.trim());
+        let resolved = resolved.canonicalize().unwrap();
+        assert_eq!(resolved, git_dir.canonicalize().unwrap());
+    }
+
+    #[test]
+    fn detect_jj_git_dir_resolves_secondary_workspace() {
+        let dir = tempfile::tempdir().unwrap();
+        let main_root = dir.path().join("main");
+        let secondary_root = dir.path().join("secondary");
+
+        // Set up main workspace:
+        //   main/.jj/repo/store/git_target  →  "../../../.git"
+        //   main/.git/
+        let main_jj = main_root.join(".jj");
+        let main_store = main_jj.join("repo").join("store");
+        std::fs::create_dir_all(&main_store).unwrap();
+        std::fs::write(main_store.join("git_target"), "../../../.git").unwrap();
+        let main_git = main_root.join(".git");
+        std::fs::create_dir(&main_git).unwrap();
+
+        // Set up secondary workspace:
+        //   secondary/.jj/repo  →  file pointing to main/.jj/repo (absolute path)
+        let secondary_jj = secondary_root.join(".jj");
+        std::fs::create_dir_all(&secondary_jj).unwrap();
+        let main_repo_abs = main_jj.join("repo").canonicalize().unwrap();
+        std::fs::write(secondary_jj.join("repo"), main_repo_abs.to_str().unwrap()).unwrap();
+
+        // Verify secondary workspace resolves to the same git dir.
+        let repo_content = std::fs::read_to_string(secondary_jj.join("repo")).unwrap();
+        let repo_dir = PathBuf::from(repo_content.trim());
+        assert!(repo_dir.is_dir());
+
+        let git_target =
+            std::fs::read_to_string(repo_dir.join("store").join("git_target")).unwrap();
+        let resolved = repo_dir.join("store").join(git_target.trim());
+        let resolved = resolved.canonicalize().unwrap();
+        assert_eq!(resolved, main_git.canonicalize().unwrap());


There are no integration tests for jj workspace functionality. The PR only includes unit tests for the jj.rs module itself. Consider adding integration tests that verify end-to-end behavior, such as: running hooks in a simulated jj workspace, verifying that --all-files works correctly, and ensuring that stashing is properly disabled. Without integration tests, it's difficult to verify that all the pieces work together correctly.

Copilot · 2026-02-20T10:28:23Z

crates/prek/src/jj.rs

+    let workspace_root = find_jj_dir(&cwd)
+        .and_then(|jj_dir| jj_dir.parent().map(Path::to_path_buf))
+        .unwrap_or(cwd);


On line 116, if find_jj_dir(&cwd) returns None (which shouldn't happen since we already validated it exists in detect_jj_git_dir()), or if .parent() returns None (which would be unusual for a .jj directory), the code falls back to using cwd as the workspace root. This fallback might lead to incorrect behavior where GIT_WORK_TREE points to a subdirectory instead of the actual workspace root. Consider whether this fallback is necessary or if it should be an error condition.

Suggested change

let workspace_root = find_jj_dir(&cwd)

.and_then(|jj_dir| jj_dir.parent().map(Path::to_path_buf))

.unwrap_or(cwd);

let Some(workspace_root) = find_jj_dir(&cwd)

.and_then(|jj_dir| jj_dir.parent().map(Path::to_path_buf))

else {

debug!(

"jj workspace detected, but failed to determine workspace root from cwd {}; not setting git env vars",

cwd.display()

);

return;

};

Copilot · 2026-02-20T10:28:23Z

crates/prek/src/jj.rs

+    };
+
+    let git_target_file = repo_dir.join("store").join("git_target");
+    let git_target = std::fs::read_to_string(&git_target_file).ok()?;


The new jj.rs module uses std::fs directly instead of fs_err which is the standard throughout the codebase. Using fs_err provides better error messages with file paths included automatically. Replace all instances of std::fs::read_to_string, std::fs::create_dir, etc. with their fs_err:: equivalents.

Copilot · 2026-02-20T10:28:24Z

crates/prek/src/main.rs

+    // Detect jj workspace and set GIT_DIR/GIT_WORK_TREE if needed.
+    jj::setup_git_env_for_jj();


The setup_git_env_for_jj function is called before logging is fully initialized. If there are issues in jj workspace detection, the debug messages on lines 118-122 will not be captured in the log file. Consider moving the call after logging is set up in main.rs, or document why early execution is required.

Copilot · 2026-02-20T10:28:24Z

crates/prek/src/jj.rs

+    let repo_dir_candidate = jj_dir.join("repo");
+    let repo_dir = if repo_dir_candidate.is_file() {
+        // Secondary workspace: file contains the path to the main repo dir.
+        let content = std::fs::read_to_string(&repo_dir_candidate).ok()?;


The new jj.rs module uses std::fs directly instead of fs_err which is the standard throughout the codebase. Using fs_err provides better error messages with file paths included automatically. Replace all instances of std::fs::read_to_string, std::fs::create_dir, etc. with their fs_err:: equivalents.

Copilot · 2026-02-20T10:28:25Z

crates/prek/src/cli/run/run.rs

+    let should_stash =
+        !all_files && files.is_empty() && directories.is_empty() && !*crate::jj::IS_JJ_WORKSPACE;


The should_stash condition correctly excludes jj workspaces from stashing, but the code on lines 85-87 (not shown in diff) still calls workspace.check_configs_staged() when should_stash is true. Since this function uses git::files_not_staged() which checks git's staging area, it will work correctly for git repos but may need jj-specific handling in the future. Consider verifying this works as expected in jj workspaces where configs are modified.

Copilot · 2026-02-20T10:28:25Z

docs/faq.md

+When running inside a jj workspace, prek:
+
+- Resolves the backing Git directory from `.jj/repo/store/git_target`, so all internal git commands work even when there is no `.git` directory.
+- Uses `jj diff --name-only` instead of `git diff --staged` to collect changed files, since jj does not use Git's staging area.


The documentation states that prek "Uses jj diff --name-only instead of git diff --staged", but jj diff --name-only shows changes in the current changeset (working copy changes), not just the equivalent of staged files. This is conceptually different from git's staging area. Consider clarifying that jj operates on the working copy changeset, which includes all modified files, not just a subset like git's staging area.

Suggested change

- Uses `jj diff --name-only` instead of `git diff --staged` to collect changed files, since jj does not use Git's staging area.

- Uses `jj diff --name-only` to collect files changed in the current working-copy changeset (jj does not have a separate staging area like `git diff --staged`).

Copilot · 2026-02-20T10:28:25Z

crates/prek/src/cli/run/filter.rs

+        let files = crate::jj::get_changed_files(workspace_root)
+            .await
+            .map_err(|e| anyhow::anyhow!(e))?;


The error from jj::get_changed_files() is converted to anyhow using map_err(|e| anyhow::anyhow!(e)). This is redundant since jj::Error already implements Display and std::error::Error (via thiserror), so it can be automatically converted using the ? operator or .context(). The current git code on line 397 uses ? directly without explicit error conversion.

Suggested change

let files = crate::jj::get_changed_files(workspace_root)

.await

.map_err(|e| anyhow::anyhow!(e))?;

let files = crate::jj::get_changed_files(workspace_root).await?;

Copilot · 2026-02-20T10:28:25Z

crates/prek/src/cli/run/filter.rs

+    let files = if *crate::jj::IS_JJ_WORKSPACE {
+        let files = crate::jj::get_changed_files(workspace_root)
+            .await
+            .map_err(|e| anyhow::anyhow!(e))?;


When IS_JJ_WORKSPACE is true but the jj command is not available in PATH, calling get_changed_files() will fail with a "Failed to find jj" error. This could happen if someone checks out a jj workspace on a machine without jj installed. Consider providing a more helpful error message in this scenario, or falling back to a different behavior. The error handling in filter.rs (line 393) will show the raw error which may be confusing to users.

Suggested change

.map_err(|e| anyhow::anyhow!(e))?;

.map_err(|e| {

let msg = e.to_string();

if msg.contains("Failed to find jj") {

anyhow::anyhow!(

"Detected a jj workspace, but the `jj` command was not found in PATH.\n\

Install `jj` (https://github.com/martinvonz/jj), ensure it is on your PATH,\n\

or convert this workspace to use git instead.\n\

Underlying error: {msg}"

)

} else {

anyhow::anyhow!(e)

}

})?;

prek-ci-bot · 2026-02-20T10:29:01Z

📦 Cargo Bloat Comparison

Binary size change: +0.81% (24.7 MiB → 24.9 MiB)

Expand for cargo-bloat output

Head Branch Results

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Base Branch Results

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41.0%  85.8%  10.1MiB                   And 23260 smaller methods. Use -n N to show more.
47.8% 100.0%  11.8MiB                   .text section size, the file size is 24.7MiB

j178 · 2026-02-20T13:01:07Z

Thanks! I definitely want to support jj in prek. But it needs some careful design and thought—not just patching things into the git code path.

Let’s mark this as a draft for now. Once I have a better understanding of jj, I’ll be in a much better position to review and maintain this code properly.

martijnberger · 2026-02-20T16:00:33Z

Thanks! I definitely want to support jj in prek. But it needs some careful design and thought—not just patching things into the git code path.

Agreed, ill take a proper pass at this tomorrow and do it by hand in the artisanal way

Enable prek to work inside jj workspaces, including secondary workspaces created with `jj workspace add` where there is no `.git` directory. - Add new `jj` module that detects jj workspaces and resolves the backing git directory from `.jj/repo/store/git_target` - Set GIT_DIR/GIT_WORK_TREE env vars early in startup so all git commands work transparently in jj workspaces - Use `jj diff --name-only` instead of `git diff --staged` for file collection, since jj doesn't use git's staging area - Disable git-specific stashing/work-tree-cleaning for jj workspaces - Short-circuit merge conflict detection for jj (handles conflicts differently)

- Use EnvVars constants instead of raw string literals for GIT_DIR/GIT_WORK_TREE - Use EnvVars::is_set() instead of disallowed std::env::var_os() - Use let...else pattern per clippy::manual_let_else - Add #[instrument(level = "trace")] to get_changed_files() matching git.rs - Add doc comments to JJ static and jj_cmd() matching git.rs conventions - Import prek_consts::env_vars::EnvVars for consistency with rest of codebase - Add unit tests for find_jj_dir, colocated workspace, and secondary workspace resolution

- Add FAQ entry explaining how prek detects and works with jj workspaces - Mention jj working copy in quickstart guide's "run hooks on demand" section - Update workspace discovery docs to reference .jj alongside .git as a repository boundary

prek-ci-bot · 2026-03-14T08:54:13Z

⚡️ Hyperfine Benchmarks

Summary: 0 regressions, 0 improvements above the 10% threshold.

Environment

OS: Linux 6.14.0-1017-azure
CPU: 4 cores
prek version: prek 0.3.5+22 (bf28e7f 2026-03-14)
Rust version: rustc 1.94.0 (4a4ef493e 2026-03-02)
Hyperfine version: hyperfine 1.20.0

CLI Commands

Benchmarking basic commands in the main repo:

`prek --version`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base --version`	2.4 ± 0.2	2.2	3.4	1.02 ± 0.10
`prek-head --version`	2.4 ± 0.1	2.2	3.4	1.00

`prek list`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base list`	8.9 ± 0.1	8.7	9.4	1.00
`prek-head list`	9.0 ± 0.3	8.7	11.9	1.00 ± 0.04

`prek validate-config .pre-commit-config.yaml`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base validate-config .pre-commit-config.yaml`	3.1 ± 0.3	3.0	5.3	1.03 ± 0.11
`prek-head validate-config .pre-commit-config.yaml`	3.0 ± 0.1	3.0	3.2	1.00

`prek sample-config`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base sample-config`	2.6 ± 0.0	2.5	2.7	1.00
`prek-head sample-config`	2.6 ± 0.1	2.6	2.9	1.01 ± 0.02

Cold vs Warm Runs

Comparing first run (cold) vs subsequent runs (warm cache):

`prek run --all-files (cold - no cache)`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run --all-files`	156.4 ± 6.8	150.5	174.4	1.04 ± 0.05
`prek-head run --all-files`	151.1 ± 2.0	149.1	155.9	1.00

`prek run --all-files (warm - with cache)`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run --all-files`	152.1 ± 2.5	148.3	156.6	1.00
`prek-head run --all-files`	152.3 ± 2.2	149.5	158.1	1.00 ± 0.02

Full Hook Suite

Running the builtin hook suite on the benchmark workspace:

`prek run --all-files (full builtin hook suite)`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run --all-files`	151.8 ± 2.2	148.7	156.6	1.00
`prek-head run --all-files`	153.8 ± 12.0	149.1	236.0	1.01 ± 0.08

Individual Hook Performance

Benchmarking each hook individually on the test repo:

`prek run trailing-whitespace --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run trailing-whitespace --all-files`	22.4 ± 0.4	21.6	23.3	1.00 ± 0.03
`prek-head run trailing-whitespace --all-files`	22.3 ± 0.4	21.7	23.3	1.00

`prek run end-of-file-fixer --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run end-of-file-fixer --all-files`	28.6 ± 1.9	26.6	33.1	1.00
`prek-head run end-of-file-fixer --all-files`	28.8 ± 2.3	26.0	34.4	1.01 ± 0.11

`prek run check-json --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-json --all-files`	13.0 ± 0.3	12.4	14.1	1.06 ± 0.04
`prek-head run check-json --all-files`	12.3 ± 0.3	11.9	13.1	1.00

`prek run check-yaml --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-yaml --all-files`	12.0 ± 0.2	11.8	12.5	1.00
`prek-head run check-yaml --all-files`	12.1 ± 0.2	11.8	12.6	1.00 ± 0.02

`prek run check-toml --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-toml --all-files`	12.2 ± 0.3	11.7	12.9	1.00 ± 0.03
`prek-head run check-toml --all-files`	12.2 ± 0.3	11.8	12.8	1.00

`prek run check-xml --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-xml --all-files`	12.1 ± 0.2	11.8	12.6	1.00
`prek-head run check-xml --all-files`	12.2 ± 0.3	11.8	13.0	1.01 ± 0.03

Installation Performance

Benchmarking hook installation (fast path hooks skip Python setup):

`prek install-hooks (cold - no cache)`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base install-hooks`	4.9 ± 0.1	4.9	5.0	1.00
`prek-head install-hooks`	4.9 ± 0.1	4.9	5.1	1.00 ± 0.02

`prek install-hooks (warm - with cache)`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base install-hooks`	4.8 ± 0.1	4.8	4.9	1.00
`prek-head install-hooks`	4.9 ± 0.1	4.7	5.0	1.01 ± 0.03

File Filtering/Scoping Performance

Testing different file selection modes:

`prek run (staged files only)`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run`	18.6 ± 0.1	18.4	18.9	1.00
`prek-head run`	18.7 ± 0.1	18.5	19.0	1.00 ± 0.01

`prek run --files '*.json' (specific file type)`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run --files '*.json'`	7.5 ± 0.1	7.4	8.0	1.01 ± 0.02
`prek-head run --files '*.json'`	7.5 ± 0.1	7.3	7.6	1.00

Workspace Discovery & Initialization

Benchmarking hook discovery and initialization overhead:

`prek run --dry-run --all-files (measures init overhead)`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run --dry-run --all-files`	12.6 ± 0.5	12.2	14.3	1.00 ± 0.04
`prek-head run --dry-run --all-files`	12.6 ± 0.2	12.3	13.2	1.00

Meta Hooks Performance

Benchmarking meta hooks separately:

`prek run check-hooks-apply --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-hooks-apply --all-files`	14.3 ± 0.1	14.1	14.5	1.09 ± 0.06
`prek-head run check-hooks-apply --all-files`	13.1 ± 0.7	12.5	14.4	1.00

`prek run check-useless-excludes --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run check-useless-excludes --all-files`	12.7 ± 0.1	12.5	12.8	1.00 ± 0.01
`prek-head run check-useless-excludes --all-files`	12.7 ± 0.1	12.5	12.9	1.00

`prek run identity --all-files`

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
`prek-base run identity --all-files`	11.1 ± 0.1	10.9	11.3	1.00
`prek-head run identity --all-files`	11.2 ± 0.1	11.0	11.4	1.01 ± 0.01

Copilot

Pull request overview

Copilot reviewed 17 out of 17 changed files in this pull request and generated 6 comments.

crates/prek/src/jj.rs

+    let git_dir = git_dir.canonicalize()?;
+
+    if git_dir.exists() {
+        Ok(Some(git_dir))
+    } else {
+        Ok(None)
+    }


crates/prek/src/git.rs

 pub(crate) fn git_cmd(summary: &str) -> Result<Cmd, Error> {
    let mut cmd = Cmd::new(GIT.as_ref().map_err(|&e| Error::GitNotFound(e))?, summary);
    cmd.arg("-c").arg("core.useBuiltinFSMonitor=false");
+    crate::repo::apply_git_env(&mut cmd);



crates/prek/src/workspace.rs

    /// Check if all configuration files are staged in git.
    pub(crate) async fn check_configs_staged(&self) -> Result<()> {
+        if !repo::requires_staged_configs() {
+            return Ok(());
+        }
+


crates/prek/src/main.rs

+mod jj;
 mod languages;
 mod printer;
 mod process;
 #[cfg(all(unix, feature = "profiler"))]
 mod profiler;
+mod repo;
 #[cfg(unix)]


crates/prek/tests/run.rs

+fn run_in_non_colocated_jj_workspace() -> Result<()> {
+    let Some(mut init) = jj_cmd(".") else {
+        return Ok(());
+    };


crates/prek/tests/builtin_hooks.rs

+#[test]
+fn check_case_conflict_in_non_colocated_jujutsu_workspace() -> Result<()> {
+    let Some(mut init) = jj_cmd(".") else {
+        return Ok(());
+    };


martijnberger requested a review from j178 as a code owner February 20, 2026 10:17

Copilot AI review requested due to automatic review settings February 20, 2026 10:17

Copilot started reviewing on behalf of martijnberger February 20, 2026 10:18 View session

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j178 marked this pull request as draft February 20, 2026 12:57

martijnberger added 4 commits March 14, 2026 09:41

Document jj (Jujutsu) workspace support

ca08373

- Add FAQ entry explaining how prek detects and works with jj workspaces - Mention jj working copy in quickstart guide's "run hooks on demand" section - Update workspace discovery docs to reference .jj alongside .git as a repository boundary

Obviously did not run format

1ec9701

martijnberger force-pushed the jj-workspace-support branch from 38087b6 to 1ec9701 Compare March 14, 2026 08:48

Refactor repository backend for Jujutsu support

dd4eb52

martijnberger force-pushed the jj-workspace-support branch from 7fa78a9 to dd4eb52 Compare March 14, 2026 14:07

martijnberger requested a review from Copilot March 14, 2026 15:01

Copilot started reviewing on behalf of martijnberger March 14, 2026 15:02 View session

Copilot AI reviewed Mar 14, 2026

View reviewed changes

		// Detect jj workspace and set GIT_DIR/GIT_WORK_TREE if needed.
		jj::setup_git_env_for_jj();

		let should_stash =
		!all_files && files.is_empty() && directories.is_empty() && !*crate::jj::IS_JJ_WORKSPACE;

	- Uses `jj diff --name-only` instead of `git diff --staged` to collect changed files, since jj does not use Git's staging area.
	- Uses `jj diff --name-only` to collect files changed in the current working-copy changeset (jj does not have a separate staging area like `git diff --staged`).

-            .map_err(|e| anyhow::anyhow!(e))?;
+            .map_err(|e| {
+                let msg = e.to_string();
+                if msg.contains("Failed to find jj") {
+                    anyhow::anyhow!(
+                        "Detected a jj workspace, but the `jj` command was not found in PATH.\n\
+                         Install `jj` (https://github.com/martinvonz/jj), ensure it is on your PATH,\n\
+                         or convert this workspace to use git instead.\n\
+                         Underlying error: {msg}"
+                    )
+                } else {
+                    anyhow::anyhow!(e)
+                }
+            })?;

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Motivation

Changes

New: crates/prek/src/jj.rs

Modified files

Documentation

Test plan

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📦 Cargo Bloat Comparison

Head Branch Results

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j178 commented Feb 20, 2026

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⚡️ Hyperfine Benchmarks

prek --version

prek list

prek validate-config .pre-commit-config.yaml

prek sample-config

prek run --all-files (cold - no cache)

prek run --all-files (warm - with cache)

martijnberger commented Feb 20, 2026 •

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New: `crates/prek/src/jj.rs`

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`prek --version`

`prek list`

`prek validate-config .pre-commit-config.yaml`

`prek sample-config`

`prek run --all-files (cold - no cache)`

`prek run --all-files (warm - with cache)`

`prek run --all-files (full builtin hook suite)`

`prek run trailing-whitespace --all-files`

`prek run end-of-file-fixer --all-files`

`prek run check-json --all-files`

`prek run check-yaml --all-files`

`prek run check-toml --all-files`

`prek run check-xml --all-files`

`prek install-hooks (cold - no cache)`

`prek install-hooks (warm - with cache)`

`prek run (staged files only)`

`prek run --files '*.json' (specific file type)`

`prek run --dry-run --all-files (measures init overhead)`

`prek run check-hooks-apply --all-files`

`prek run check-useless-excludes --all-files`

`prek run identity --all-files`