# Riff, the Refining Diff

Riff is a wrapper around `diff` that highlights which parts of lines have changed.

![Screenshot of riff in action](screenshot.png 'git show')

Unchanged parts of changed lines are shown in yellow.

`riff` also [helpfully highlights conflicts and merge commits](#more-features).

Much like `git`, Riff sends its output to a pager, trying these in order:

1. Whatever is specified in the `$PAGER` environment variable
1. [moar](https://github.com/walles/moar) because it is nice
1. `less` because it is ubiquitous

# Usage

```
git diff | riff
```

Or if you do...

```
git config --global pager.diff riff
git config --global pager.show riff
git config --global pager.log riff
git config --global interactive.diffFilter "riff --color=on"
```

... then all future `git diff`, `git show` and `git log --patch` output will be
refined.

Or you can use `riff` as an alias for `diff`:

```
riff file1.txt file2.txt
```

## Configuration

You can configure `riff` by setting the `RIFF` environment variable to one or
more (space separated) command line options.

For example, set `RIFF=--no-adds-only-special` to disable adds-only special
highlighting.

# Installation

## With [Homebrew](https://brew.sh)

```
brew install riff
```

## With [Archlinux User Repository (AUR)](https://aur.archlinux.org/packages/riffdiff)

```
paru -S riffdiff
```

## From [the Rust Crate](https://crates.io/crates/riffdiff)

```
cargo install riffdiff
```

## Manual Install

1. Go [here](https://github.com/walles/riff/releases/latest) and download the
   correct binary for your platform

   - If no binary exists for your platform, please [report
     it](https://github.com/walles/riff/issues)

1. `chmod a+x riff-*`
1. `mv riff-* /usr/local/bin/riff`
1. Optionally followed by this to have riff highlight `git` output by default:

```
git config --global pager.diff riff
git config --global pager.show riff
git config --global pager.log riff
git config --global interactive.diffFilter "riff --color=on"
```

# See Also

[This VSCode extension for improved Git commit message
editing](https://marketplace.visualstudio.com/items?itemName=walles.git-commit-message-plus)
is nice. Yes, I wrote it and I'm tooting my own horn here.

Good choice if you (like me!) are [using VSCode for Git commit message
editing](https://jonasbn.github.io/til/vscode/integrate_with_cli.html).

# More Features

`riff` can highlight conflict markers created by `git`:

![Screenshot of riff highlighting conflict markers](screenshot-diff2-conflict.png 'riff < file-with-conflict-markers.txt')

`riff` highlighting a `git` merge commits highlighting

![Screenshot of riff highlighting merge commits](screenshot-git-merge.png)

# Development

If you put example input and output in the `testdata` directory, then `cargo test` will verify that they match.

On mismatches, you can run `testdata-examples.sh` to compare current output to
the expected output for all examples, and optionally update expectations.

Invoke `ci.sh` to run the same thing as CI.

Invoke `benchmark.py` to get numbers for how fast your current source code is
versus earlier releases.

Invoke `git log -p | cargo run --` to demo highlighting.

## Making a new release

Just invoke `./release.sh` and follow instructions.

If you want to test the release script without actually releasing anything, do:

```
./release.sh --dry
```

# TODO

## Misc

- Render ESC characters in the diff as Unicode ␛
- `--help`: Only print installing-into-`$PATH` help if we aren't already being
  executed from inside of the `$PATH`
- Add test for never changing the number of lines in the input, that
  messes up `git add -p` behavior.
- Make sure we highlight the output of `git show --stat` properly
- Given three files on the command line, we should pass them and any
  options on to `diff3` and highlight the result

# TODO future

- Detect moved blocks and use a number as a prefix for both the add
  and the remove part of the move. Highlight any changes just like
  for other changes.

# DONE

- Make a main program that can read input from stdin and print it to
  stdout.
- Make the main program identify different kinds of lines by prefix
  and color them accordingly. Use the same color scheme as `git`.
- Make the main program identify blocks of lines that have been
  replaced by another block of lines.
- Make the Refiner not highlight anything if either old or new is
  empty
- Use <https://crates.io/crates/diffus> to refine hunks
- Build refined hunks and print them
- Highlight `^diff`, `^index`, `^+++` and `^---` lines in bold white
- Prefix all added / removed lines with the correct ANSI color code
- Don't highlight the initial `+` / `-` on added / removed lines
- Make sure we get the linefeeds right in diffs, try
  `git show 28e074bd0fc246d1caa3738432806a94f6773185` with and without `riff`.
- Visualize added line endings
- Visualize removed line endings
- Visualize removed linefeed at end of file properly
- Visualize adding a missing linefeed at end of file properly
- Visualize missing linefeed at end of file as part of the context
  properly
- Refine `ax`->`bx\nc` properly
- Strip all color from the input before handling it to enable users to
  set Git's pager.diff and pager.show variables to 'riff' without also
  needing to set color.diff=false.
- If stdout is a terminal, pipe the output to a pager using the
  algorithm described under `core.pager` in `git help config`.
- You can do `git diff | riff` and get reasonable output.
- Do not highlight anything if there are "too many" differences between the
  sections. The point here is that we want to highlight changes, but if it's a
  _replacement_ rather than a change then we don't want to highlight it.
- Refine by word rather than by character
  - Test case `git show 2ac5b06`: Should highlight all of both `some` and
    `one or`.
- Do some effort to prevent fork loops if people set `$PAGER` to `riff`
- Add support for `--help`
- Add support for `--version`
- Print help and bail if stdin is a terminal
- On exceptions, print the current version just like `--version`
- On exceptions, print a link to the issue tracker
- Add test case verifying that the `Inspired by` part of
  `git show 77c8f77 -- bin/riff` is highlighted as an upside down L.
- Find out how the LCS algorithm scales and improve the heuristic for
  when not to call it.
- Tune the upper bound on how large regions we should attempt to refine
- Make a CI script
- Set up CI calling the CI script
- Document `ci.sh`'s existence
- Figure out cross compiling to Linux and macOS ARM (look into `cross` which
  uses Docker for cross compiling)
- Make a release script
- Document `release.sh`'s existence
- Verify that the Linux binary works
- Document install instructions
- Make a public release
- Remedy `release.sh` FIXMEs
- Add a trailing whitespace analysis pass to the Refiner
- Let the Refiner highlight whitespace errors among the added lines in
  reverse red.
- Highlight whitespace in added parts only
- Add highlighting of non-leading tabs to the whitespace analysis
- Profile and see if we can go faster
- In `ci.sh`, add a test case verifying that our exception handler prints
  backtraces in release builds (should fail when stripping the release binary)
- In `ci.sh`, add a test case verifying that our exception handler prints line
  numbers for the `riff` frames in the backtraces, in release builds. This
  should fail when stripping the release binary.
- Require line numbers in backtraces in release builds
- Make the Linux binary smaller
- Put argv contents in crash report
- Handle plain non-git diff files
- Given two files on the command line, we should pass them on to `diff` and
  highlight the result.
- Support `riff -b path1 path2` to diff files ignoring whitespace
- Bound how-much-to-highlight restriction by number of characters highlighted
  rather than by number of tokens highlighted
- Get ourselves some kind of benchmark suite / example(s)
- Do `git show 5e0a1b2b13528f40299e78e3bfa590d9f96637af` and scroll to the end.
  How should we visualize the reformatting of the No-newline-at-eof code?
- Do `git show 0f5dd84` and think about how to visualize one line
  changing to itself with a comma at the end plus a bunch of entirely
  new lines. Think of a constant array getting one or more extra
  members.
- Do `git show -b 77c8f77` and think about what rule we should use to
  highlight the leading spaces of the `+ refined` and `+ page` lines
  at the end of the file.
- Do `git show 57f27da` and think about what rule we should use to get
  the REVERSE vs reversed() lines highlighted.
- Think about how to visualize an added line break together with some
  indentation on the following line.
- Make sure we can handle a `git` conflict
  resolution diff. File format is described at
  http://git-scm.com/docs/git-diff#_combined_diff_format.