feat: vcs: support Jujutsu as a diff-provider

Author: poliorcetics

helix-term/Cargo.toml

@@ -31,10 +31,12 @@ assets = [
 ]
 
 [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

@@ -21,9 +21,11 @@ gix = { version = "0.73.0", features = ["attributes", "parallel", "status"], def
 imara-diff =  "0.2.0"
 anyhow = "1"
 log = "0.4"
+tempfile = { version = "3.13", optional = true }
 
 [features]
 git = ["gix"]
+jj = ["tempfile"]
 
 [dev-dependencies]
 tempfile.workspace = true

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")),
+        );
+    }
+}