hew

A fast, review-first terminal patch viewer, in Rust.

hew reads a unified diff and opens it in an interactive review UI, displaying GitHub-PR-style threaded comments loaded from a sidecar JSON file. Source selection (working tree, revs, two files) is delegated to git — you just pipe a diff in.

hew = to cut/shape a block with an axe. Same "chunk/block" lineage as a diff hunk. Three letters, fast to type. Inspired by hunk, rebuilt from zero as a native single binary.

Install

cargo install --path .
# or
cargo build --release   # → target/release/hew

Usage

hew consumes a unified patch and nothing else — from a file, or stdin:

hew change.patch                 # review a patch file
git diff HEAD | hew              # review the working tree (piped)
git show <rev> | hew             # review a commit
git diff <a> <b> | hew           # compare two refs
hew - < change.patch             # explicit stdin

hew change.patch --json          # print the parsed changeset as JSON, no TUI

Load review comments from a sidecar JSON file:

hew change.patch --comments review.json

Reload automatically when the patch or comments file changes on disk:

hew change.patch --comments review.json --watch

Since hew is read-only, --watch is the editing workflow: edit review.json (or regenerate the patch) in another window and the view refreshes. Watching only applies to file inputs — a stdin patch can't be re-read.

Options

Flag	Meaning
FILE (positional)	Patch file to review. Omit or use - for stdin.
--comments <FILE>	Sidecar JSON of review comments to load.
--json	Print the parsed changeset as JSON and exit (no TUI).
--watch	Reload the patch/comments files when they change on disk.

Keys

Key	Action
j / k (or ↓/↑)	Move one line
Ctrl-D / Ctrl-U	Half page down / up
Space / b (or Ctrl-F/Ctrl-B, PageDown/PageUp)	Page down / up
Ctrl-E / Ctrl-Y	Scroll viewport one line (cursor stays in view)
g / G (or Home/End)	Jump to top / bottom
[ / ]	Jump to previous / next file
n / N	Jump to next / previous comment
← / →	Focus the file list / the diff pane
Ctrl-B	Toggle the file list sidebar
Tab / s	Toggle unified ↔ split (side-by-side) layout
y	Copy the selected line(s) to the clipboard
Esc	Clear the line selection
Ctrl-L	Force a full repaint
q	Quit

Mouse: click a file in the sidebar to open it, click a diff line to place the cursor, drag to select a range of lines, and use the wheel to scroll the pane under the pointer. Scrolling the file list just moves the list — it leaves the selected file unchanged. Drag the sidebar/diff divider to resize the sidebar. Both panes show a scrollbar when content overflows. y copies the selection to the clipboard via OSC 52 (works in terminals that support it).

Multi-file diffs show a file list sidebar, grouped by directory (a dim header per directory, files listed by basename with +adds/-dels, current file highlighted), and the diff pane shows only the selected file. Keyboard navigation acts on the focused pane: focus the sidebar with ← and j/k/g/G move between files (the diff follows); → (or Enter) returns to the diff, where j/k/paging scroll within that one file. [/] switch files from either pane. The focused pane's selection is brighter.

Unified stacks -/+ lines; split shows old on the left and new on the right (like git delta --side-by-side), pairing changed lines across a divider. Toggling keeps the cursor on the same line.

hew is a read-only viewer: comments are loaded from a sidecar and displayed (gutter markers + popup), never edited.

Comment sidecar format

{
  "threads": [
    {
      "file": "src/main.rs",
      "side": "new",
      "range": { "start": 18, "end": 22 },
      "resolved": false,
      "comments": [
        { "author": "agent", "body": "This match arm is unreachable." },
        { "author": "you",   "body": "Good catch." }
      ]
    }
  ]
}

• side: "new" (added/context, RIGHT) or "old" (removed, LEFT)
• range: a single line uses start == end
• comments[0] is the thread root; the rest are replies
• author, resolved, id, created_at are optional (sensible defaults)

A bare [ ...threads... ] array is also accepted.

Examples

Real {patch + comments} from public PRs live in examples/:

hew examples/misskey-ja.patch   --comments examples/misskey-ja.comments.json
hew examples/rust-long-en.patch --comments examples/rust-long-en.comments.json

See examples/README.md for how to fetch more.

Design & roadmap

hew is intentionally a read-only viewer: no persistence, no GitHub/network integration, no patch apply/edit/merge, no structural (AST) diff. It offers unified and split layouts, syntax highlighting (syntect + two-face's bat syntax set for broad language coverage, Monokai Extended Bright theme, pure-Rust fancy-regex), sidecar comment threads, and --watch reload.

Planned: a tree-sitter highlighting backend, theme selection, and a loopback session server so an agent/CLI can drive a running TUI.

Note: hew parses plain unified diffs, not git format-patch mailbox output (gh pr diff --patch). Use a .diff/git diff stream instead.