Allow viewing past commits in Zed (#27636)

This PR adds functionality for loading the diff for an arbitrary git
commit, and displaying it in a tab. To retrieve the diff for the commit,
I'm using a single `git cat-file --batch` invocation to efficiently load
both the old and new versions of each file that was changed in the
commit.

Todo

* Features
* [x] Open the commit view when clicking the most recent commit message
in the commit panel
  * [x] Open the commit view when clicking a SHA in a git blame column
  * [x] Open the commit view when clicking a SHA in a commit tooltip
  * [x] Make it work over RPC
  * [x] Allow buffer search in commit view
* [x] Command palette action to open the commit for the current blame
line
* Styling
* [x] Add a header that shows the author, timestamp, and the full commit
message
  * [x] Remove stage/unstage buttons in commit view
  * [x] Truncate the commit message in the tab
* Bugs
  * [x] Dedup commit tabs within a pane
  * [x] Add a tooltip to the tab

Release Notes:

- Added the ability to show past commits in Zed. You can view the most
recent commit by clicking its message in the commit panel. And when
viewing a git blame, you can show any commit by clicking its sha.

crates/git/src/repository.rs

@@ -1,18 +1,18 @@
-use crate::status::GitStatus;
+use crate::commit::parse_git_diff_name_status;
+use crate::status::{GitStatus, StatusCode};
 use crate::{Oid, SHORT_SHA_LENGTH};
 use anyhow::{Context as _, Result, anyhow};
 use collections::HashMap;
 use futures::future::BoxFuture;
 use futures::{AsyncWriteExt, FutureExt as _, select_biased};
 use git2::BranchType;
-use gpui::{AsyncApp, BackgroundExecutor, SharedString};
+use gpui::{AppContext as _, AsyncApp, BackgroundExecutor, SharedString};
 use parking_lot::Mutex;
 use rope::Rope;
 use schemars::JsonSchema;
 use serde::Deserialize;
 use std::borrow::{Borrow, Cow};
 use std::ffi::{OsStr, OsString};
-use std::future;
 use std::path::Component;
 use std::process::{ExitStatus, Stdio};
 use std::sync::LazyLock;
@@ -21,6 +21,10 @@ use std::{
     path::{Path, PathBuf},
     sync::Arc,
 };
+use std::{
+    future,
+    io::{BufRead, BufReader, BufWriter, Read},
+};
 use sum_tree::MapSeekTarget;
 use thiserror::Error;
 use util::ResultExt;
@@ -133,6 +137,18 @@ pub struct CommitDetails {
     pub committer_name: SharedString,
 }
 
+#[derive(Debug)]
+pub struct CommitDiff {
+    pub files: Vec<CommitFile>,
+}
+
+#[derive(Debug)]
+pub struct CommitFile {
+    pub path: RepoPath,
+    pub old_text: Option<String>,
+    pub new_text: Option<String>,
+}
+
 impl CommitDetails {
     pub fn short_sha(&self) -> SharedString {
         self.sha[..SHORT_SHA_LENGTH].to_string().into()
@@ -206,6 +222,7 @@ pub trait GitRepository: Send + Sync {
 
     fn show(&self, commit: String) -> BoxFuture<Result<CommitDetails>>;
 
+    fn load_commit(&self, commit: String, cx: AsyncApp) -> BoxFuture<Result<CommitDiff>>;
     fn blame(&self, path: RepoPath, content: Rope) -> BoxFuture<Result<crate::blame::Blame>>;
 
     /// Returns the absolute path to the repository. For worktrees, this will be the path to the
@@ -405,6 +422,108 @@ impl GitRepository for RealGitRepository {
             .boxed()
     }
 
+    fn load_commit(&self, commit: String, cx: AsyncApp) -> BoxFuture<Result<CommitDiff>> {
+        let Some(working_directory) = self.repository.lock().workdir().map(ToOwned::to_owned)
+        else {
+            return future::ready(Err(anyhow!("no working directory"))).boxed();
+        };
+        cx.background_spawn(async move {
+            let show_output = util::command::new_std_command("git")
+                .current_dir(&working_directory)
+                .args([
+                    "--no-optional-locks",
+                    "show",
+                    "--format=%P",
+                    "-z",
+                    "--no-renames",
+                    "--name-status",
+                ])
+                .arg(&commit)
+                .stdin(Stdio::null())
+                .stdout(Stdio::piped())
+                .stderr(Stdio::piped())
+                .output()
+                .map_err(|e| anyhow!("Failed to start git show process: {e}"))?;
+
+            let show_stdout = String::from_utf8_lossy(&show_output.stdout);
+            let mut lines = show_stdout.split('\n');
+            let parent_sha = lines.next().unwrap().trim().trim_end_matches('\0');
+            let changes = parse_git_diff_name_status(lines.next().unwrap_or(""));
+
+            let mut cat_file_process = util::command::new_std_command("git")
+                .current_dir(&working_directory)
+                .args(["--no-optional-locks", "cat-file", "--batch=%(objectsize)"])
+                .stdin(Stdio::piped())
+                .stdout(Stdio::piped())
+                .stderr(Stdio::piped())
+                .spawn()
+                .map_err(|e| anyhow!("Failed to start git cat-file process: {e}"))?;
+
+            use std::io::Write as _;
+            let mut files = Vec::<CommitFile>::new();
+            let mut stdin = BufWriter::with_capacity(512, cat_file_process.stdin.take().unwrap());
+            let mut stdout = BufReader::new(cat_file_process.stdout.take().unwrap());
+            let mut info_line = String::new();
+            let mut newline = [b'\0'];
+            for (path, status_code) in changes {
+                match status_code {
+                    StatusCode::Modified => {
+                        writeln!(&mut stdin, "{commit}:{}", path.display())?;
+                        writeln!(&mut stdin, "{parent_sha}:{}", path.display())?;
+                    }
+                    StatusCode::Added => {
+                        writeln!(&mut stdin, "{commit}:{}", path.display())?;
+                    }
+                    StatusCode::Deleted => {
+                        writeln!(&mut stdin, "{parent_sha}:{}", path.display())?;
+                    }
+                    _ => continue,
+                }
+                stdin.flush()?;
+
+                info_line.clear();
+                stdout.read_line(&mut info_line)?;
+
+                let len = info_line.trim_end().parse().with_context(|| {
+                    format!("invalid object size output from cat-file {info_line}")
+                })?;
+                let mut text = vec![0; len];
+                stdout.read_exact(&mut text)?;
+                stdout.read_exact(&mut newline)?;
+                let text = String::from_utf8_lossy(&text).to_string();
+
+                let mut old_text = None;
+                let mut new_text = None;
+                match status_code {
+                    StatusCode::Modified => {
+                        info_line.clear();
+                        stdout.read_line(&mut info_line)?;
+                        let len = info_line.trim_end().parse().with_context(|| {
+                            format!("invalid object size output from cat-file {}", info_line)
+                        })?;
+                        let mut parent_text = vec![0; len];
+                        stdout.read_exact(&mut parent_text)?;
+                        stdout.read_exact(&mut newline)?;
+                        old_text = Some(String::from_utf8_lossy(&parent_text).to_string());
+                        new_text = Some(text);
+                    }
+                    StatusCode::Added => new_text = Some(text),
+                    StatusCode::Deleted => old_text = Some(text),
+                    _ => continue,
+                }
+
+                files.push(CommitFile {
+                    path: path.into(),
+                    old_text,
+                    new_text,
+                })
+            }
+
+            Ok(CommitDiff { files })
+        })
+        .boxed()
+    }
+
     fn reset(
         &self,
         commit: String,