Handle grep output

- Handle standard filepath:code and filepath:line_number:code output
  as produced by `git grep`, `rg -H`, `grep -H`, etc (with -n for line
  numbers).

- Retain the match highlighting as produced by the grep tool, and
  expose it in delta's color output styled with grep-match-style.
  (Note that --color=always is needed to retain the color if piping
  into delta, but not for `git grep` when delta is configured as git's
  pager)

- Special handling of -p, and -W options of `git grep`: these display
  the function context in which the matches occur.

- `navigate` keybindings jump between match function contexts under
  `git grep -p` and between matching lines under `git grep -W`.

Thanks @zachriggle for the proposal.
Fixes #769

1 files changed, 12 insertions, 0 deletions

diff --git a/README.md b/README.md
index 8cc6b0a0..8a2aa1f4 100644
--- a/README.md
+++ b/README.md
@@ -23,6 +23,7 @@
     show = delta
     log = delta
     blame = delta
+    grep = delta
     reflog = delta
 
 [interactive]
@@ -64,6 +65,7 @@ Code evolves, and we all spend time studying diffs. Delta aims to make this both
   - [Choosing colors (styles)](#choosing-colors-styles)
   - [Line numbers](#line-numbers)
   - [Side-by-side view](#side-by-side-view)
+  - [Grep](#grep)
   - ["Features": named groups of settings](#features-named-groups-of-settings)
   - [Custom themes](#custom-themes)
   - [diff-highlight and diff-so-fancy emulation](#diff-highlight-and-diff-so-fancy-emulation)
@@ -151,6 +153,7 @@ Here's what `git show` can look like with git configured to use delta:
 - Git style strings (foreground color, background color, font attributes) are supported for >20 stylable elements
 - Side-by-side view with line-wrapping
 - Line numbering
+- Handles grep output with file paths from `rg`, `git grep`, `grep`, etc
 - `diff-highlight` and `diff-so-fancy` emulation modes
 - Stylable box/line decorations to draw attention to commit, file and hunk header sections.
 - Support for Git's `--color-moved` feature.
@@ -410,6 +413,15 @@ In contrast, the long replacement line in the right panel overflows by almost an
 For control over the details of line wrapping, see `--wrap-max-lines`, `--wrap-left-symbol`, `--wrap-right-symbol`, `--wrap-right-percent`, `--wrap-right-prefix-symbol`, `--inline-hint-style`.
 Line wrapping was implemented by @th1000s.
 
+### Grep
+
+Delta applies syntax-highlighting and other enhancements to standard grep output such as from `git grep`, [ripgrep](https://github.com/BurntSushi/ripgrep/) (aka `rg`), grep, etc.
+To use with `git grep`, set delta as the pager for `grep` in the `[pager]` section of your gitconfig. See the example at the [top of the page](#get-started).
+Output from other grep tools can be piped to delta: e.g. `rg -Hn --color=always`, `grep -Hn --color=always`, etc.
+To customize the colors and syntax highlighting, see `grep-match-line-style`, `grep-match-word-style`, `grep-contexct-line-style`, `grep-file-style`, `grep-line-number-style`.
+Ripgrep's `rg --json` output format is supported; this avoids certain file name parsing ambiguities that are inevitable with the standard grep output formats.
+Note that `git grep` can display the "function context" for matches and that delta handles this output specially: see the `-p` and `-W` options of `git grep`.
+
 ### "Features": named groups of settings
 
 All delta options can go under the `[delta]` section in your git config file. However, you can also use named "features" to keep things organized: these are sections in git config like `[delta "my-feature"]`. Here's an example using two custom features: