Diffing gems in GIT.

Recently, I’ve been doing some patching on fpm and today I also started writing some tests for the changes I made. One change required that the gem in the repository used for testing had a bin in it so I modified the .gemspec and rebuild it.

After building and about to push it, I thought on how it must seem to the maintainer when somebody sends a pull request for a binary blob. I would like to know what really changed in there without having to go checkout the internals myself. How wonderful would life be if we could just use git diff to show the differences.

Here is a way to do just that using .gitattributes and a little shell script:

misc/gemdiff.sh:

#!/bin/bash
echo "============== metadata =============="
tar -xOf $1 metadata.gz 2>/dev/null | gunzip -c 2>/dev/null
echo "============== checksums ============="
tar -xOf $1 checksums.yaml.gz 2>/dev/null | gunzip -c 2>/dev/null
echo "=============== files ================"
tar -xOf $1 data.tar.gz 2>/dev/null | tar -xvOzf - 2>&1

.gitattributes:

*.gem diff=gemdiff

.git/config:

[diff "gemdiff"]
    textconv = misc/gemdiff.sh

The result looks like this:

diff --git a/spec/fixtures/gem/example/example-1.0.gem b/spec/fixtures/gem/example/example-1.0.gem
index 0241779..f762e52 100644
--- a/spec/fixtures/gem/example/example-1.0.gem
+++ b/spec/fixtures/gem/example/example-1.0.gem
@@ -3,19 +3,17 @@
 name: example
 version: !ruby/object:Gem::Version
   version: '1.0'
-  prerelease: 
 platform: ruby
 authors:
 - sample author
 autorequire: 
 bindir: bin
 cert_chain: []
-date: 2012-03-15 00:00:00.000000000 Z
+date: 2014-05-01 00:00:00.000000000 Z
 dependencies:
 - !ruby/object:Gem::Dependency
   name: dependency1
   requirement: !ruby/object:Gem::Requirement
-    none: false
     requirements:
     - - ! '>='
       - !ruby/object:Gem::Version
@@ -23,7 +21,6 @@ dependencies:
   type: :runtime
   prerelease: false
   version_requirements: !ruby/object:Gem::Requirement
-    none: false
     requirements:
     - - ! '>='
       - !ruby/object:Gem::Version
@@ -31,7 +28,6 @@ dependencies:
 - !ruby/object:Gem::Dependency
   name: dependency2
   requirement: !ruby/object:Gem::Requirement
-    none: false
     requirements:
     - - ! '>='
       - !ruby/object:Gem::Version
@@ -39,42 +35,59 @@ dependencies:
   type: :runtime
   prerelease: false
   version_requirements: !ruby/object:Gem::Requirement
-    none: false
     requirements:
     - - ! '>='
       - !ruby/object:Gem::Version
         version: '0'
 description: sample description
 email: sample email
-executables: []
+executables:
+- example
 extensions: []
 extra_rdoc_files: []
-files: []
+files:
+- bin/example
 homepage: http://sample-url/
 licenses: []
+metadata: {}
 post_install_message: 
 rdoc_options: []
 require_paths:
 - lib
 required_ruby_version: !ruby/object:Gem::Requirement
-  none: false
   requirements:
   - - ! '>='
     - !ruby/object:Gem::Version
       version: '0'
 required_rubygems_version: !ruby/object:Gem::Requirement
-  none: false
   requirements:
   - - ! '>='
     - !ruby/object:Gem::Version
       version: '0'
 requirements: []
 rubyforge_project: 
-rubygems_version: 1.8.18
+rubygems_version: 2.0.14
 signing_key: 
-specification_version: 3
+specification_version: 4
 summary: sample summary
 test_files: []
 has_rdoc: 
 ============== checksums =============
+---
+!binary "U0hBMQ==":
+  metadata.gz: !binary |-
+    MjYwNGQ5MDZjYTE0MjY5MWQyZTA5Yzk0MjgyYjk2ZGM0ZTk3YzE3Mw==
+  data.tar.gz: !binary |-
+    YmZmYzJlNDU0ZGNmMDEzZjJmZGExYWZiYWE2ZjBjYTQ2MTMzYzFkNA==
+!binary "U0hBNTEy":
+  metadata.gz: !binary |-
+    MzYyYTVlNDk0ODRiNzdhNDBjOWE0ZmEyOGM0NjAzNzg3M2VlZTA4MzgzZDAw
+    ZjVhMjc5ZjFjYTIzOTk2MWFhYjZmMjNiNmVkNzRlMzMzMTdiOTMxMzlmM2Nl
+    ZGE3ZDc5ZDRkNjUwNDE1ODkzNDkxNDhmNmI5YmUyYjg2NjEwMjk=
+  data.tar.gz: !binary |-
+    MGY3NzllNTgwOGQ2YzhmOGUwNjlkMTk5NTlhOTIzZjJkZTkyMjdiNzQxZDQ3
+    NDc4ZjU5NGU1YTA4ODc1NzQwNTc3OWNlOWZkZjMwNWFmMDE3MWE4ZDUzNGY3
+    NDE0NGVmMjA4MDM1MDA4ZjdiMzliNWIwYTNiNDVkMWExZmIyYTY=
 =============== files ================
+bin/example
+#!/usr/bin/env ruby

Life.wonderfulness++;

Leave a Reply