Syntax Highlighted Diffs

Question

How to make Git display diffs in the terminal with code syntax highlight, like what GitHub does? I mean not only with green for addition and red for deletion, but also with code syntax highlighting.

Answer 1

I recently wrote a tool that does this: https://github.com/dandavison/delta

Answer 2

It's possible to write a git diff driver that passes the files through Pygments' pygmentize tool.

First, define a pygmentize wrapper with your preferred pygmentize settings (formatter / style / filters) in ~/bin/pygmentize-term:

#!/bin/sh
exec pygmentize -f terminal256 -O bg=dark,style=trac "$@"

Then, define a generic "diff with syntax highlighting" program in ~/bin/hldiff:

#!/bin/bash
set -euo pipefail

# Diff two files with syntax highlighting using pygmentize.

# pygmentize-term should be a pygmentize wrapper with your preferred
# pygmentize settings (formatter / style / filters)

function prepare() {
    local fn=$1

    # Work around https://bitbucket.org/birkenfeld/pygments-main/issues/1437
    if [[ "$fn" == /dev/null ]]
    then
        return
    fi

    local lexer
    lexer=$(pygmentize -N "$fn")
    #printf "Detected lexer of %q as %q\n" "$fn" "$lexer" 1>&2

    if [[ "$lexer" == text ]]
    then
        expand "$fn" | pygmentize-term -g
    else
        expand "$fn" | pygmentize-term -l "$lexer"
    fi
}

# Use colordiff (instead of diff --color=always) solely because it
# produces consistent formatting on a per-line basis, saving us from
# having to keep track of state across lines
diff=(colordiff --color=yes)

for arg in "$@"
do
    if [[ $arg == -* ]]
    then
        diff+=("$arg")
    else
        exec {fd}< <(prepare "$arg")
        diff+=(/dev/fd/$fd)
    fi
done

sed=(
    sed
    # replace "all attributes off" (used by Pygmentize to turn off
    # bold) with "normal intensity"
    -e 's/\x1b\[00m/\x1b[22m/g'

    # Replace colordiff's foreground colors with some dark background
    # colors. You can customize them here.
    -e 's/^\x1b\[0;36m/\x1b[0;36;48;5;23m/' # cyan
    -e 's/^\x1b\[0;31m/\x1b[0;31;48;5;52m/' # red
    -e 's/^\x1b\[0;32m/\x1b[0;32;48;5;22m/' # green

    # Extend background color across the entire terminal window width
    -e 's/\x1b\[0;0m$/\x1b\[K\x1b[0m/'
)

"${diff[@]}" | "${sed[@]}"

The above can be used instead of diff to get a diff of two files with syntax highlighting.

To get git to use it, define a git diff driver wrapper for the above in ~/bin/git-hldiff-driver:

#!/bin/bash
set -euo pipefail

# Program suitable for GIT_EXTERNAL_DIFF, which will syntax-highlight differences.

hldiff -u "$2" "$5" || true

You can now set GIT_EXTERNAL_DIFF to the above wrapper script to get git to show diffs with syntax highlighting:

$ GIT_EXTERNAL_DIFF=~/bin/git-hldiff-driver git diff

To get git show to use it, you need to specify the --ext-diff switch:

$ GIT_EXTERNAL_DIFF=~/bin/git-hldiff-driver git show --ext-diff

Note that by default git show will send its output through a pager (less), which will cause the background color to not be displayed quite properly, so also add --no-pager to prevent that.