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Hacky syntax highlighting in git diff

Normally git diff would color additions green and deletions red. This is cool, but it would be even cooler if it adds syntax highlighting to those lines. This is a git pager that does so.

It parses the diff output and picks up the SHAs of files with additions and deletions. It uses CodeRay to highlight each file and then it extracts the lines that are shown in the diff. It then uses term/ansicolor to make a gradient from the CodeRay color and the diff color (red for deletion, green for addition) and uses it to replace the original.

I tried using rugged instead of shelling out to git show – it was faster overall, but it did incur a noticeable start up time.

Check out the image below for a demo.

#!/usr/bin/env ruby
require 'coderay'
require 'term/ansicolor'
require 'optparse'
# --- Adjusting colors -------------------------------------------------------
RGB = Term::ANSIColor::RGBTriple
Attribute = Term::ANSIColor::Attribute
Color = Term::ANSIColor
GREEN = RGB.new(0, 256, 0)
RED = RGB.new(256, 0, 0)
GRAY = RGB.new(32, 32, 32)
ADJUSTMENTS = {}
GRADIENTS = {}
def adjust(text, target)
open = adjust_seq("\e[37m", target)
adjusted = text.chomp.gsub(/\e\[[0-9;]+m/) { |seq| adjust_seq(seq, target) }
"#{open}#{adjusted}"
end
def adjust_seq(seq, target)
key = [seq, target]
ADJUSTMENTS[key] ||=
begin
escapes = []
seq[/\d+(;\d+)*/].split(';').map(&:to_i).each do |number|
case number
when 0 then escapes << ["\e[0m", gradient_to(255, target)]
when 1 then escapes << "\e[1m"
when 4 then escapes << "\e[4m"
when 30..37 then escapes << gradient_to(number - 30, target)
when 40..47 then escapes << gradient_to(number - 30, target, :background)
else escapes << seq
end
end
escapes.join('')
end
end
def gradient_to(num, target, background = false)
key = [num, target, background]
GRADIENTS[key] ||=
begin
triple = triple(num)
target = triple.gradient_to(target)[8]
html = target.html
method = background ? "on_#{html}" : html
Attribute[method].apply
end
end
def triple(num)
Attribute[num].to_rgb_triple
end
# --- Parsing git diffs ------------------------------------------------------
FORMATS = {
'Gemfile' => :ruby,
'rb' => :ruby,
'c' => :c,
'h' => :c,
'cpp' => :cpp,
'cxx' => :cpp,
'hpp' => :cpp,
'clj' => :clojure,
'css' => :css,
'erb' => :erb,
'go' => :go,
'java' => :java,
'js' => :javascript,
'json' => :json,
'php' => :php,
'lua' => :lua,
'py' => :python,
'sass' => :sass,
'scss' => :scss,
'sql' => :sql,
'xml' => :xml,
'yml' => :yaml,
'yaml' => :yaml,
}
CACHED_OBJECTS = {}
def show(sha, path)
return [] if sha =~ /^0+$/
cached = CACHED_OBJECTS.delete sha
return cached if cached
format = FORMATS[path[/(\w+)$/, 1]]
code = `git show #{sha} 2> /dev/null`
code = File.read(path) if code.empty?
code = CodeRay.scan(code, format).terminal if format
CACHED_OBJECTS[sha] = code.lines
end
def process(options)
new = nil
old = nil
remaining = nil
old_file = nil
new_file = nil
old_hash = nil
new_hash = nil
while gets
stripped = $_.gsub(/(\e\[[0-9;]*m)*/, '')
case stripped
when /^index (\w+)..(\w+)/
old_hash = $1
new_hash = $2
puts $_
# @@ -1,4 +1,4 @@
when /^@@ -(\d+)(?:,(\d+))? \+(\d+)(?:,(\d+))? @@/
old_start, old_length = $1.to_i - 1, ($2 || 1).to_i
new_start, new_length = $3.to_i - 1, ($4 || 1).to_i
remaining = old_length + new_length
puts $_
when /^\+\+\+ (.*)$/
new_file = $1.sub(/^[ab]\//, '')
old = show old_hash, old_file
new = show new_hash, new_file
puts $_
when /^--- (.*)$/
old_file = $1.sub(/^[ab]\//, '')
puts $_
when /^ /
if remaining.nil? || remaining <= 0
puts $_
next
elsif options[:highlight]
puts " #{adjust(new[new_start], GRAY)}"
else
puts $_
end
old_start += 1
new_start += 1
when /^\+/
puts adjust("+#{new[new_start]}", GREEN)
new_start += 1
when /^-/
puts adjust("-#{old[old_start]}", RED)
old_start += 1
else
puts $_
end
end
end
options = {}
OptionParser.new do |opts|
opts.banner = "Usage: #{File.basename(__FILE__)} [options]"
opts.on("-h", "--[no-]highlight", "Highlight all the code") do |v|
options[:highlight] = v
end
end.parse!
begin
process(options)
rescue Errno::EPIPE
exit 0
end
[core]
pager = /path/to/diff-syntax-highlight.rb | less
@skanev

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@skanev skanev commented Oct 4, 2014

Cool idea.

There is a regression though – /^ / matches some commit messages. I'll fiddle a bit with it and see if it looks good if it makes a gradient to gray 😄

@valo

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@valo valo commented Oct 4, 2014

I thought that the remaining variable will catch the commit messages... Do you see the commit messages changed?

@skanev

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@skanev skanev commented Oct 5, 2014

I checked and it turns out it is never updated :) . I said it was hacky, right?

Anyway, here's a new version. It fixes the commit messages and it also blends the other text toward gray. You can experiment with the gradient and see if you like it less or more.

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