Closes#26866
### Summary
Adds a git graph to Zed, accessible via the `git_graph::Open` action if
a project has an active repository. There's still more to do, but this
is a solid foundation to expand upon. The code structure is in line with
Zed's codebase and shouldn't require architectural changes to add
missing features.
The git graph can be opened via the command palette (`git graph: open`)
or by binding a key to `git_graph::Open`. It's available when the
project has an active git repository.
### Architecture
Similar to the Debugger, the git graph is split between a data layer and
a view/UI layer. When the view layer is rendering, it queries the data
layer for its active state. This setup allows the data layer to lazily
request graph data (only when needed for rendering), abstracts collab
from the view layer, allows most of the data loading to happen on a
background thread, and makes caching easy to implement.
#### Graph Loading
The graph data is loaded in two phases:
1. `Repository::graph_data()` streams commit structure (SHA, parents,
refs) in chunks of 1000 via `git log`
2. `CommitDataReader` lazily fetches full commit details (author,
timestamp, subject) on-demand using a persistent `git cat-file --batch`
process
This two-phase approach makes the initial loading of the graph as fast
as possible, because `git log` takes significantly longer when all the
needed graph data is queried through it. Zed then lazily loads commits
in the user's viewport through `cat-file --batch`. This makes scrolling
to any place in the graph extremely snappy and benefits the
collaborative architecture by only fetching data needed to render the
graph. It also allows Zed to share commit data between different graph
visualizations (e.g., date order vs. topological order).
#### Performance
Tested on both the Zed and LLVM repositories with good performance in
both cases. The two-phase loading approach and lazy fetching keep the UI
responsive even with large commit histories.
#### Testing
I added property testing that builds randomized commit graphs and
verifies that the graph is constructed correctly. This also works as an
integration test and will be expanded in the future to test collab graph
visualization, graph filtering, commit actions, etc.
### New Crate
- `git_graph` (GPL-licensed) — contains UI and graph computation logic
### Not Yet Implemented
- Remote repository support (collab)
- Filtering by branch
- Commit actions (checkout, cherry-pick, etc.)
- Search
- Open commit view for selected commit
- Resizable columns
- Column filtering
#### Reference
<img width="1624" height="976" alt="Screenshot 2025-01-22 at 8 15 39 PM"
src="https://github.com/user-attachments/assets/0f10924a-3964-462f-b320-42d84d02f7bf"
/>
Special thanks to [Alberto Slavica](https://github.com/pyundev) for
submitting #44405, which was a good base to work off of.
Release Notes:
- git: Add initial version of git graph
---------
Co-authored-by: pyundev <pyundev@users.noreply.github.com>
Co-authored-by: Cole Miller <cole@zed.dev>
Co-authored-by: Zed Zippy <234243425+zed-zippy[bot]@users.noreply.github.com>
Remco Smits