feat: vcs: support Jujutsu as a diff-provider

helix-term/Cargo.toml

@@ -13,10 +13,12 @@ repository.workspace = true
 homepage.workspace = true
 
 [features]
-default = ["git"]
+default = ["git", "jj"]
 unicode-lines = ["helix-core/unicode-lines", "helix-view/unicode-lines"]
 integration = ["helix-event/integration_test"]
+# VCS features
 git = ["helix-vcs/git"]
+jj = ["helix-vcs/jj"]
 
 [[bin]]
 name = "hx"

helix-vcs/Cargo.toml

@@ -24,9 +24,11 @@ imara-diff = "0.1.7"
 anyhow = "1"
 
 log = "0.4"
+tempfile = { version = "3.13", optional = true }
 
 [features]
 git = ["gix"]
+jj = ["tempfile"]
 
 [dev-dependencies]
 tempfile = "3.14"

helix-vcs/src/jj.rs

@@ -0,0 +1,282 @@
+//! Jujutsu works with several backends and could add new ones in the future. Private builds of
+//! it could also have private backends. Those make it hard to use `jj-lib` since it won't have
+//! access to newer or private backends and fail to compute the diffs for them.
+//!
+//! Instead in case there *is* a diff to base ourselves on, we copy it to a tempfile or just use the
+//! current file if not.
+
+use std::path::Path;
+use std::process::Command;
+use std::sync::Arc;
+
+use anyhow::{Context, Result};
+use arc_swap::ArcSwap;
+
+use crate::FileChange;
+
+pub(super) fn get_diff_base(repo: &Path, file: &Path) -> Result<Vec<u8>> {
+    let file_relative_to_root = file
+        .strip_prefix(repo)
+        .context("failed to strip JJ repo root path from file")?;
+
+    let tmpfile = tempfile::NamedTempFile::with_prefix("helix-jj-diff-")
+        .context("could not create tempfile to save jj diff base")?;
+    let tmppath = tmpfile.path();
+
+    let copy_bin = if cfg!(windows) { "copy.exe" } else { "cp" };
+
+    let status = Command::new("jj")
+        .arg("--repository")
+        .arg(repo)
+        .args([
+            "--ignore-working-copy",
+            "diff",
+            "--revision",
+            "@",
+            "--config-toml",
+        ])
+        // Copy the temporary file provided by jujutsu to a temporary path of our own,
+        // because the `$left` directory is deleted when `jj` finishes executing.
+        .arg(format!(
+            "ui.diff.tool = ['{exe}', '$left/{base}', '{target}']",
+            exe = copy_bin,
+            base = file_relative_to_root.display(),
+            // Where to copy the jujutsu-provided file
+            target = tmppath.display(),
+        ))
+        // Restrict the diff to the current file
+        .arg(file)
+        .stdout(std::process::Stdio::null())
+        .stderr(std::process::Stdio::null())
+        .status()
+        .context("failed to execute jj diff command")?;
+
+    let use_jj_path = status.success() && std::fs::metadata(tmppath).map_or(false, |m| m.len() > 0);
+    // If the copy call inside `jj diff` succeeded, the tempfile is the one containing the base
+    // else it's just the original file (so no diff). We check for size since `jj` can return
+    // 0-sized files when there are no diffs to present for the file.
+    let diff_base_path = if use_jj_path { tmppath } else { file };
+
+    // If the command succeeded, it means we either copied the jujutsu base or the current file,
+    // so there should always be something to read and compare to.
+    std::fs::read(diff_base_path).context("could not read jj diff base from the target")
+}
+
+pub(crate) fn get_current_head_name(repo: &Path) -> Result<Arc<ArcSwap<Box<str>>>> {
+    // See <https://github.com/martinvonz/jj/blob/main/docs/templates.md>
+    //
+    // This will produce the following:
+    //
+    // - If there are no branches:    `vyvqwlmsvnlkmqrvqktpuluvuknuxpmm`
+    // - If there is a single branch: `vyvqwlmsvnlkmqrvqktpuluvuknuxpmm (master)`
+    // - If there are 2+ branches:    `vyvqwlmsvnlkmqrvqktpuluvuknuxpmm (master, jj-diffs)`
+    //
+    // Always using the long id makes it easy to share it with others, which would not be the
+    // case for shorter ones: they could have a local change that renders it ambiguous.
+    let template = r#"separate(" ", change_id, surround("(", ")", branches.join(", ")))"#;
+
+    let out = Command::new("jj")
+        .arg("--repository")
+        .arg(repo)
+        .args([
+            "--ignore-working-copy",
+            "log",
+            "--color",
+            "never",
+            "--revisions",
+            "@", // Only display the current revision
+            "--no-graph",
+            "--no-pager",
+            "--template",
+            template,
+        ])
+        .output()?;
+
+    if !out.status.success() {
+        anyhow::bail!("jj log command executed but failed");
+    }
+
+    let out = String::from_utf8(out.stdout)?;
+
+    let rev = out
+        .lines()
+        .next()
+        // Contrary to git, if a JJ repo exists, it always has at least two revisions:
+        // the root (zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz), which cannot be focused, and the current
+        // one, which exists even for brand new repos.
+        .context("should always find at least one line")?;
+
+    Ok(Arc::new(ArcSwap::from_pointee(rev.into())))
+}
+
+pub(crate) fn for_each_changed_file(
+    repo: &Path,
+    callback: impl Fn(Result<FileChange>) -> bool,
+) -> Result<()> {
+    let out = Command::new("jj")
+        .arg("--repository")
+        .arg(repo)
+        .args([
+            "--ignore-working-copy",
+            "diff",
+            "--color",
+            "never",
+            "--revision",
+            "@", // Only display the current revision
+            "--no-pager",
+            "--types",
+        ])
+        .output()?;
+
+    if !out.status.success() {
+        anyhow::bail!("jj log command executed but failed");
+    }
+
+    let out = String::from_utf8(out.stdout)?;
+
+    for line in out.lines() {
+        let Some((status, path)) = line.split_once(' ') else {
+            continue;
+        };
+
+        let Some(change) = status_to_change(status, path) else {
+            continue;
+        };
+
+        if !callback(Ok(change)) {
+            break;
+        }
+    }
+
+    Ok(())
+}
+
+pub(crate) fn open_repo(repo_path: &Path) -> Result<()> {
+    assert!(
+        repo_path.join(".jj").exists(),
+        "no .jj where one was expected: {}",
+        repo_path.display(),
+    );
+
+    let status = Command::new("jj")
+        .args(["--ignore-working-copy", "root"])
+        .stdout(std::process::Stdio::null())
+        .stderr(std::process::Stdio::null())
+        .status()?;
+
+    if status.success() {
+        Ok(())
+    } else {
+        anyhow::bail!("not a valid JJ repo")
+    }
+}
+
+/// Associate a status to a `FileChange`.
+fn status_to_change(status: &str, path: &str) -> Option<FileChange> {
+    if let rename @ Some(_) = find_rename(path) {
+        return rename;
+    }
+
+    // Syntax: <https://github.com/martinvonz/jj/blob/f9cfa5c9ce0eacd38e961c954e461e5e73067d22/cli/src/diff_util.rs#L97-L101>
+    Some(match status {
+        "FF" | "LL" | "CF" | "CL" | "FL" | "LF" => FileChange::Modified { path: path.into() },
+        "-F" | "-L" => FileChange::Untracked { path: path.into() },
+        "F-" | "L-" => FileChange::Deleted { path: path.into() },
+        "FC" | "LC" => FileChange::Conflict { path: path.into() },
+        // We ignore gitsubmodules here since they not interesting in the context of
+        // a file editor.
+        _ => return None,
+    })
+}
+
+fn find_rename(path: &str) -> Option<FileChange> {
+    let (start, rest) = path.split_once('{')?;
+    let (from, rest) = rest.split_once(" => ")?;
+    let (to, end) = rest.split_once('}')?;
+
+    Some(FileChange::Renamed {
+        from_path: format!("{start}{from}{end}").into(),
+        to_path: format!("{start}{to}{end}").into(),
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use std::path::PathBuf;
+
+    use super::*;
+
+    #[test]
+    fn test_status_to_change() {
+        let p = "helix-vcs/src/lib.rs";
+        let pb = PathBuf::from(p);
+
+        for s in ["FF", "LL", "CF", "CL", "FL", "LF"] {
+            assert_eq!(
+                status_to_change(s, p).unwrap(),
+                FileChange::Modified { path: pb.clone() }
+            );
+        }
+        for s in ["-F", "-L"] {
+            assert_eq!(
+                status_to_change(s, p).unwrap(),
+                FileChange::Untracked { path: pb.clone() }
+            );
+        }
+        for s in ["F-", "L-"] {
+            assert_eq!(
+                status_to_change(s, p).unwrap(),
+                FileChange::Deleted { path: pb.clone() }
+            );
+        }
+        for s in ["FC", "LC"] {
+            assert_eq!(
+                status_to_change(s, p).unwrap(),
+                FileChange::Conflict { path: pb.clone() }
+            );
+        }
+        for s in ["GG", "LG", "ARO", "", " ", "  "] {
+            assert_eq!(status_to_change(s, p), None);
+        }
+    }
+
+    #[test]
+    fn test_find_rename() {
+        fn check(path: &str, expected: Option<(&str, &str)>) {
+            let result = find_rename(path);
+
+            assert_eq!(
+                result,
+                expected.map(|(f, t)| FileChange::Renamed {
+                    from_path: f.into(),
+                    to_path: t.into()
+                })
+            )
+        }
+
+        // No renames
+        check("helix-term/Cargo.toml", None);
+        check("helix-term/src/lib.rs", None);
+
+        // Rename of first element in path
+        check(
+            "{helix-term => helix-term2}/Cargo.toml",
+            Some(("helix-term/Cargo.toml", "helix-term2/Cargo.toml")),
+        );
+        // Rename of final element in path
+        check(
+            "helix-term/{Cargo.toml => Cargo.toml2}",
+            Some(("helix-term/Cargo.toml", "helix-term/Cargo.toml2")),
+        );
+        // Rename of a single dir in the middle
+        check(
+            "helix-term/{src => src2}/lib.rs",
+            Some(("helix-term/src/lib.rs", "helix-term/src2/lib.rs")),
+        );
+        // Rename of two dirs in the middle
+        check(
+            "helix-term/{src/ui => src2/ui2}/text.rs",
+            Some(("helix-term/src/ui/text.rs", "helix-term/src2/ui2/text.rs")),
+        );
+    }
+}

helix-vcs/src/lib.rs

@@ -4,6 +4,8 @@
 
 #[cfg(feature = "git")]
 mod git;
+#[cfg(feature = "jj")]
+mod jj;
 
 mod diff;
 
@@ -72,7 +74,7 @@ pub fn for_each_changed_file(
 }
 
 /// Creation and update methods
-#[cfg_attr(not(feature = "git"), allow(unused))]
+#[cfg_attr(not(any(feature = "git", feature = "jj")), allow(unused))]
 impl DiffProviderRegistry {
     /// Register a provider (if any is found) for the given path.
     pub fn add(&mut self, path: &Path) {
@@ -90,9 +92,11 @@ pub fn add(&mut self, path: &Path) {
             return;
         };
 
-        let result = match provider {
+        let result: Result<(Arc<Path>, PossibleDiffProvider)> = match provider {
             #[cfg(feature = "git")]
             PossibleDiffProvider::Git => self.add_file_git(repo_path),
+            #[cfg(feature = "jj")]
+            PossibleDiffProvider::JJ => self.add_file_jj(repo_path),
         };
 
         match result {
@@ -190,26 +194,49 @@ fn add_file_git(&mut self, repo_path: &Path) -> Result<(Arc<Path>, PossibleDiffP
             Err(err) => Err(err),
         }
     }
+
+    /// Add the JJ repo to the known providers *if* it isn't already known.
+    #[cfg(feature = "jj")]
+    fn add_file_jj(&mut self, repo_path: &Path) -> Result<(Arc<Path>, PossibleDiffProvider)> {
+        // Don't build a JJ repo object if there is already one for that path.
+        if let Some((key, DiffProvider::JJ(_))) = self.providers.get_key_value(repo_path) {
+            return Ok((Arc::clone(key), PossibleDiffProvider::JJ));
+        }
+
+        match jj::open_repo(repo_path) {
+            Ok(()) => {
+                let key = Arc::from(repo_path);
+                self.providers
+                    .insert(Arc::clone(&key), DiffProvider::JJ(Arc::clone(&key)));
+                Ok((key, PossibleDiffProvider::JJ))
+            }
+            Err(err) => Err(err),
+        }
+    }
 }
 
 /// A union type that includes all types that implement [DiffProvider]. We need this type to allow
 /// cloning [DiffProviderRegistry] as `Clone` cannot be used in trait objects.
-///
-/// `Copy` is simply to ensure the `clone()` call is the simplest it can be.
 #[derive(Clone)]
 pub enum DiffProvider {
     #[cfg(feature = "git")]
     Git(gix::ThreadSafeRepository),
+    /// For [`jujutsu`](https://github.com/martinvonz/jj), we don't use the library but instead we
+    /// call the binary because it can dynamically load backends, which the JJ library doesn't know about.
+    #[cfg(feature = "jj")]
+    JJ(Arc<Path>),
 }
 
-#[cfg_attr(not(feature = "git"), allow(unused))]
+#[cfg_attr(not(any(feature = "git", feature = "jj")), allow(unused))]
 impl DiffProvider {
     fn get_diff_base(&self, file: &Path) -> Result<Vec<u8>> {
         // We need the */ref else we're matching on a reference and Rust considers all references
-        // inhabited. In our case
+        // inhabited.
         match *self {
             #[cfg(feature = "git")]
             Self::Git(ref repo) => git::get_diff_base(repo, file),
+            #[cfg(feature = "jj")]
+            Self::JJ(ref repo) => jj::get_diff_base(repo, file),
         }
     }
 
@@ -217,6 +244,8 @@ fn get_current_head_name(&self) -> Result<Arc<ArcSwap<Box<str>>>> {
         match *self {
             #[cfg(feature = "git")]
             Self::Git(ref repo) => git::get_current_head_name(repo),
+            #[cfg(feature = "jj")]
+            Self::JJ(ref repo) => jj::get_current_head_name(repo),
         }
     }
 
@@ -224,6 +253,8 @@ fn for_each_changed_file(&self, f: impl Fn(Result<FileChange>) -> bool) -> Resul
         match *self {
             #[cfg(feature = "git")]
             Self::Git(ref repo) => git::for_each_changed_file(repo, f),
+            #[cfg(feature = "jj")]
+            Self::JJ(ref repo) => jj::for_each_changed_file(repo, f),
         }
     }
 }
@@ -233,6 +264,9 @@ pub enum PossibleDiffProvider {
     /// Possibly a git repo rooted at the stored path (i.e. `<path>/.git` exists)
     #[cfg(feature = "git")]
     Git,
+    /// Possibly a git repo rooted at the stored path (i.e. `<path>/.jj` exists)
+    #[cfg(feature = "jj")]
+    JJ,
 }
 
 /// Does *possible* diff provider auto detection. Returns the 'root' of the workspace
@@ -240,20 +274,20 @@ pub enum PossibleDiffProvider {
 /// We say possible because this function doesn't open the actual repository to check if that's
 /// actually the case.
 fn get_possible_provider(path: &Path) -> Option<(&Path, PossibleDiffProvider)> {
-    if cfg!(feature = "git") {
-        #[cfg_attr(not(feature = "git"), allow(unused))]
-        fn check_path(path: &Path) -> Option<(&Path, PossibleDiffProvider)> {
-            #[cfg(feature = "git")]
-            if path.join(".git").try_exists().ok()? {
-                return Some((path, PossibleDiffProvider::Git));
-            }
-
-            None
-        }
+    // TODO(poliorcetics): make checking order configurable
+    let checks: &[(&str, PossibleDiffProvider)] = &[
+        #[cfg(feature = "jj")]
+        (".jj", PossibleDiffProvider::JJ),
+        #[cfg(feature = "git")]
+        (".git", PossibleDiffProvider::Git),
+    ];
 
+    if !checks.is_empty() {
         for parent in path.ancestors() {
-            if let Some(path_and_provider) = check_path(parent) {
-                return Some(path_and_provider);
+            for &(repo_indic, pdp) in checks {
+                if let Ok(true) = parent.join(repo_indic).try_exists() {
+                    return Some((parent, pdp));
+                }
             }
         }
     }

helix-vcs/src/status.rs

@@ -1,5 +1,6 @@
 use std::path::{Path, PathBuf};
 
+#[derive(Debug, PartialEq, Eq)]
 pub enum FileChange {
     Untracked {
         path: PathBuf,