Making packaging Maven projects easier

September 12, 2011 in en, fedora, packaging

There are two recent changes to our Java guidelines in Fedora and use of Maven when packaging that I’d like to mention today

Maven dependency mapping macros

Thing I haven’t blogged about yet but it’s pretty important: We have new macros for maven depmaps in Fedora. In the past when you wanted to map certain groupId:artifactId to a file in _javadir, you had to include snippet like this in your spec:


%add_to_maven_depmap com.google.guava guava 05 JPP guava
%add_to_maven_depmap com.google.collections google-collections 05 JPP guava

This tells our maven that com:google:guava:guava and com.google.collections:google-collections can be found in one of the repositories as JPP/guava.jar. It meant you had to know the groupId:artifactId and other information, plus it was extremely easy to make a mistake here causing all sorts of trouble. Current code doing the same thing:


%add_maven_depmap JPP-guava.pom guava.jar -a "com.google.collections:google-collections"

We parse the pom file and get groupId:artifactId from it, plus we do additional sanity checks such as:

  • naming of pom and jar file have to be consistent
  • jar file has to exist if packaging type is not pom

If you need additional mappings you can easily add them. There are few other options for this new macro useful in certain situations.

Maven test deps skipping

Long story short: When you use -Dmaven.test.skip=true in Fedora packages you no longer need to patch those test dependencies out of pom.xml.

We’ve had Apache Maven in Fedora for quite some time and packaging using Maven has been getting easier over time due to small tweaks to our packaging macros and guidelines changes. However there has been one problem that’s been bugging all Java packagers and was especially confusing for those starting to package software built with Maven. The problem is that Maven creates a tree of dependencies before it starts building the project, but it includes test dependencies even when tests are being skipped.

Skipping tests is sometimes necessary due to problems with koji, or dependencies and up until now we had to either patch those tests dependencies from pom.xml or use custom dependency mappings (ugly concept in itself).

Last week I decided it’s about time someone did something about this, so I dug in the Maven code and created a solution (more of a hack really) that is already included in Fedora. If you want the gory details, you can read the patch itself (I advise against it). I’ll try to make the patch work properly so that it can be included in mainstream code.

I can just hope that packagers will find these changes helpful, but general feedback has been positive.

Addition of fedpkg rpmlint

July 27, 2011 in fedora, packaging, rpmlint

*Edit:* Yes, there is fedpkg lint but it somewhat limited so read on. Instead of addition of “rpmlint” command Pingou will improve current lint

Recently I was trying to help OpenSuSE guys with some updates to their Java stack and I was sent link to their build system. I noticed a file called jpackage-utils-rpmlintrc and this got me thinking…

What if we added rpmlint command to fedpkg with per-package rpmlint ignore settings? Turns out Pingou took my idea and implemented it in under an hour :-)

An example run:


$ fedpkg rpmlint
plexus-interpolation.spec: W: invalid-url Source0: plexus-interpolation-1.14.tar.xz
0 packages and 1 specfiles checked; 0 errors, 1 warnings.

plexus-interpolation.spec: W: invalid-url Source0: plexus-interpolation-1.14.tar.xz
plexus-interpolation.src: W: spelling-error %description -l en_US interpolator -> interpolate, interpolation, interrogator
plexus-interpolation.src: W: invalid-url Source0: plexus-interpolation-1.14.tar.xz
1 packages and 1 specfiles checked; 0 errors, 3 warnings.
2 packages run
rpmlint has not been run on rpm files but should

OK, so we can run rpmlint on spec, srpm and binary rpms with single command. But I don’t like to see the same warnings all the time, because that means I will probably miss real problems when they appear. For this fedpkg rpmlint uses .rpmlint file as additional rpmlint config. So after creating:


$ cat > .rpmlint << EOF
# we have scm checkout with comment in spec
addFilter('invalid-url')
# false positive
addFilter('spelling-error.*interpolator')
EOF
$ fedpkg rpmlint
0 packages and 1 specfiles checked; 0 errors, 0 warnings.

1 packages and 1 specfiles checked; 0 errors, 0 warnings.
2 packages run
rpmlint has not been run on rpm files but should

Cool right? Pierre sent patch with this feature to fedpkg developers, so hopefully we’ll see this addition soon. I then plan to add custom .rpmlint configurations to all my packages so that they will be warning-free.

Print expanded SourceX: urls from spec files

July 26, 2011 in fedora, packaging, python, rpm, script

I’ve noticed quite a few times that people add comments to their Source0: urls without macros to seemingly simplify manual downloading. It looks like this:

Name: jsoup
Version: 1.6.1
...
# http://jsoup.org/packages/jsoup-1.6.1-sources.jar
Source0: http://%{name}.org/packages/%{name}-%{version}-sources.jar

This creates burden on maintainers to keep those urls up-to-date as version changes, so I created simple python script for printing out Source urls from spec files:


#!/usr/bin/python

import rpm
import sys

ts=rpm.TransactionSet()
spec_obj = ts.parseSpec(sys.argv[1])

sources = spec_obj.sources

for url, num, flags in sources:
print url

Chmod this +x, put into your PATH and enjoy by giving it path to spec file.
*Edit*: Probably much nicer way to do the same thing already present on your system (courtesy of Alexander Kurtakov):

spectool X.spec

I knew there was something like this, but forgot what it was. Oh well…2 minutes lost.

Getting your Java Application in Linux: Guide for Developers (Part 2)

April 20, 2011 in fedora, howto, java, packaging

Ant and Maven

Last time I have written about general rules of engagement for Java developers if they want to make lives of packagers easier. Today I’ll focus on specifics of two main build systems in use today: Ant and Maven, but more so on Maven for reasons I’ll state in a while.

Ant

Ant is (or at least used to be) most widely deployed build system in Java ecosystem. There are probably multiple reasons for it, but generally it’s because Ant is relatively simple. In *NIX world Ant is equivalent of pure make (and build.xml of Makefile). build.xml is just that: an XML, and it has additional extensions to simplify common tasks (calling javac, javadoc, etc.). So the question is:

I am starting a new java project. How can I use Ant properly to make life easier for you?

The most simple answer? DON’T! It might seem harsh and ignorant of bigger picture and it probably is. But I believe it’s also true that Ant is generally harder to package than Maven. Ant build.xml files are almost always unique pieces of art in themselves and as such can be a pain to package. I am always reminded of following quote when I have to dig through some smart build.xml system:

Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it.

  –Brian Kernighan

And I have a feeling some people try to be really clever when writing their build.xml files. That said, I understand there are times when using Ant is just too tempting so I’ll include a few tips for it anyway.

Use apache-ivy extension for dependencies

One of main problem with and is handling of various dependencies. Usually, they are in some subdirectory of main tree, some jars versioned, some not, some patched without any note about it…in other words nightmare in itself. Apache-ivy extension helps here because it works with dependency metadata that packagers can use to figure out real build dependencies including versions. We can also be sure that no dependencies are patched in one way or the other.

Ivy is nice for developers as well. It will make your source tarballs much smaller (You do have source tarballs right?!) and your build.xml nicer. I won’t include any examples here because I believe that Ivy documentation is indeed very good.

One lib/ to rule them all

In case you really don’t want to use Ivy, make sure you place all your dependencies in one directory in top level of your project (don’t scatter your dependencies, even if you are using multiple sub-projects). This directory should ideally be called lib/. It should contain your dependencies named as ${name}-${version}.jar. Most of the time you should include license files for every dependency you bundle, because you are becoming distributors and for most licenses this means you have to provide full text of the license. For licenses use identical name as jar filenames, but use “.license” suffix. All in all, make it easy to figure out your build dependencies and play with them.

Don’t be too clever

I can’t stress this enough. Try to keep your build.xml files to the bare minimum. Understanding ten 30 KiB big build.xml files with multiple-phase build and tests spread through 10 directories is no fun. Please think of poor packager when you write your build.xml files. I don’t mind having grey hair that much, but I’d rather if it came later rather than sooner.

Maven

And now we are coming to my favourite part. Maven is a build and project management tool that has extensive plugin support able to do almost anything developer might ask for. And all that while providing formal project structure, so that once you learn how Maven works in one project you can re-use your knowledge in other projects.

Maven goodies

Maven provides several good things for packagers such as providing clear dependencies and preventing simple patched dependencies from sneaking in. Most important advantage for packagers coming with Maven is the fact that problems are the same in all projects. Once you understand how certain Maven plugin works, you will know what to expect and what to look for. But Maven is nice not just for packagers, but also for developers.

Declarative instead of descriptive

You don’t tell Maven:

Add jar A, jar B to the classpath, then use this properies file to set-up test resources. Then compile tests (Have you compiled sources yet?) and then … and run them with X

Instead you place test files and resources into appropriate directories and Maven will take care of everything. You just need to specify your test dependencies in nice and tidy pom.xml.

Project metadata in one place

With Maven you have all project information in one place:

  • Developer contact information
  • Homepage
  • SCM URLs
  • Mailinglists
  • Issue tracker URL
  • Project reports/site generation
  • Dependencies
  • Ability modify behaviour according to architecture, OS or other property

Need I say more? Fill it out, keep it up-to-date and we will all be happy.

Great integration with other tools

Ecosystem around Maven has been growing in past years and now you will find good support for handling your pom.xml files in any major java IDE. But that is just the tip of the iceberg. There are Maven plugins adding all kinds of additional tool support. Running checkstyle on your code, helping with licensing, integration with gpg, ssh, jflex and making releases. There are plugins for that and more.

Support for Ant

If you are in process of migrating your build system from Ant to Maven, you can do it in phases. For parts of your builds you can easily run Ant with maven-ant-plugin. Good example of such migration in progress is checkstyle. In version 5.2 they introduced Maven build system while preserving their old layout and running Ant for tests.

Maven messier side

A.K.A What you need to be aware of. It’s generally quite hard to do something bad in Maven, because it won’t let you do that easily. That said, there are plugins that can make it hard for us to package your software.

maven-dependency-plugin:copy-dependencies

This specific goal can potentially cause problems because it allows to copy classes from dependencies into resulting jar files. As I wrote last time, this is unacceptable because it creates possible licensing, security and maintenance nightmares. If you need even just one class from another project, rather than copying it, add it as a dependency into pom.xml

maven-shade-plugin

Shade plugin is a very shady plugin (pun intended). It can be used to weave depdencies inside your jars while changing their package names and doing all kinds of modifications in the process. I’ll give you a small test now :-) Let’s say you have jar file with following contents:


META-INF/
META-INF/MANIFEST.MF
META-INF/maven/
META-INF/maven/org.packager/
META-INF/maven/org.packager/Pack/
META-INF/maven/org.packager/Pack/pom.properties
META-INF/maven/org.packager/Pack/pom.xml
org/
org/packager/
org/packager/signature/
org/packager/signature/SignatureReader.class
org/packager/signature/SignatureVisitor.class
org/packager/signature/SignatureWriter.class
org/packager/Pack.class

Can you tell, from looking at jar contents where is org.packager.signature subpackage coming from? Take your time, think about it. Nothing? Well here’s a hint:



org.apache.maven.plugins
maven-shade-plugin



org.objectweb.asm
org.packager




I believe this demonstrates why usage of shade plugin is evil (in 99% of cases at least). This is especially problematic if the shaded packages are part of public API of your project, because we won’t be able to simply fix this in one package, but it will cascade up the dependency chain.

maven-bundle-plugin

Bundle is one of the more controversial plugins, because it can be used both for good and bad :-) One of the most important good use cases for bundle plugin is generating OSGI bundles. Every project can easily make their jar files OSGI compatible by doing something like this:


...
bundle
...



org.apache.felix
maven-bundle-plugin
true



...

Easy right? Now to the darker side of bundle plugin. I have another example to test your skills. This one should be easier than shade plugin:


META-INF/MANIFEST.MF
META-INF/
META-INF/maven/
META-INF/maven/org.packager/
META-INF/maven/org.packager/Pack/
META-INF/maven/org.packager/Pack/pom.properties
META-INF/maven/org.packager/Pack/pom.xml
org/
org/objectweb/
org/objectweb/asm/
org/objectweb/asm/signature/
org/objectweb/asm/signature/SignatureReader.class
org/objectweb/asm/signature/SignatureVisitor.class
org/objectweb/asm/signature/SignatureWriter.class
org/packager/
org/packager/Pack.class

Problem is the same as with shade plugin (bundling of dependencies), but at least here it’s more visible in the contents of the jar and it will not poison API of the jar. Just for the record, this is how it was created:



org.apache.felix
maven-bundle-plugin
true


org.objectweb.asm.signature



Summary

Today I wrote about:

  • Ant and why you shouldn’t use it (that much)
  • Ant and how to use it if you have to
  • Maven and why it rocks for packagers and developers
  • Maven and its plugins and why they suck for packagers sometimes

There are a lot more things that can cause problems, but these are the most obvious and easily fixed. I’ll try to gather more information about things we (packagers) can do to help you (developers) a bit more and perhaps include one final part for this guide.

Getting your Java Application in Linux: Guide for Developers (Part 1)

April 8, 2011 in fedora, howto, java, packaging

Introduction to packaging Java

Packaging Java libraries and applications in Fedora has been my daily bread for almost a year now. I realized now is the time to share some of my thoughts on the matter and perhaps share a few ideas that upstream developers might find useful when dealing with Linux distributions.

This endeavour is going to be split into several posts, because there are more sub-topics I want to write about. Most of this is going to be based on my talk I did @ FOSDEM 2011. Originally I was hoping to just post the video, but it seems to be taking more time than I expected :-)

If you are not entirely familiar with status of Java on Linux systems it would be a good idea to first read a great article by Thierry Carrez called The real problem with Java in Linux distros. A short quote from that blog:

The problem is that Java open source upstream projects do not really release code. Their main artifact is a complete binary distribution, a bundle including their compiled code and a set of third-party libraries they rely on.

There is no simple solution and my suggestions are only mid-term workarounds and ways to make each other’s (upstream ↔ downstream) lives easier. Sometimes I am quite terse in suggestions, but if need be I’ll expand them later on.

Part 1: General rules of engagement

Today I am going to focus on general rules that apply to all Java projects wishing to be packaged in Linux distributions:

  • Making source releases
  • Handling Dependencies
  • Bugfix releases

For full understanding a short summary of general requirements for packages to be added to most Linux distributions:

  • All packages have to be built from source
  • No bundled dependencies used for building/running
  • Have single version of each library that all packages use

There are a lot of reasons for these rules and they have been flogged to death multiple times in various places. It mostly boils down to severe maintenance and security problems when these rules are not followed.

Making source releases

As I mentioned previously most Linux distributions rebuild packages from source even when there is an upstream release that is binary compatible. To do this we need sources obviously :-) Unfortunately quite a few (mostly Maven) projects don’t do source release tarballs. Some projects provide source releases without build scripts (build.xml or pom.xml files). Most notable examples are Apache Maven plugins. For each and every update of one of these plugins we have to checkout the source from upstream repository and generate the tarball ourselves.
All projects using Maven build system can simply make packagers’ lives easier by having following snippet in their pom.xml files:




...

maven-assembly-plugin


project




make-assembly
package

single




...


This will create -project.zip/tar.gz files containing all the files needed to rebuild package from source. I have no real advice for projects using Ant for now, but I’ll summarise them next time.

Handling dependencies

I have a feeling that most Java projects don’t spend too much time thinking about dependencies. This should change so here are a few things to think about when adding new dependencies to your project.

Verify if the dependency isn’t provided by JVM

Often packages contain unnecessary dependencies that are provided by all recent JVMs. Think twice if you really need another XML parser.

Try to pick dependencies from major projects

Major projects (apache-commons libraries, eclipse, etc.) are much more likely to be packaged and supported properly in Linux distributions. If you use some unknown small library packagers will have to package that first and this can sometimes lead to such frustrating dependency chains they will give up before packaging your software.

Do NOT patch your dependencies

Sometimes a project A does almost exactly what you want, but not quite…So you patch it and ship it with your project B as a dependency. This will cause problems for Linux distributions because you basically forked the original project A. What you should do instead is work with the developers of project A to add features you need or fix those pesky bugs.

Bugfix releases

Every software project has bugs, so sooner or later you will have to do a bugfix release. As always there are certain rules you should try to uphold when doing bugfix releases.

Use correct version numbers

This depends on your versioning scheme. I’ll assume you are using standard X.Y.Z versions for your releases. Changes in Z are smallest released changes of your project. They should mostly contain only bugfixes and unobtrusive and simple feature additions if necessary. If you want to add bigger features you should change Y part of the version.

Backward compatible

Bugfix releases have to be backwards compatible at all times. No API changes are allowed.

No changes in dependencies

You should not change dependencies or add new ones in bugfix releases. Even updating dependency to a new version can cause massive recursive need for updates or new dependencies. The only time it’s acceptable to change/add dependency version in bugfix release is when new dependency is required to fix the bug.

An excellent example of how NOT to do things was Apache Maven update from 3.0 to 3.0.1. This update changed requirements from Aether 1.7 to Aether 1.8. Aether 1.8 had new dependency on async-http-client. Async-http-client depends on netty, jetty 7.x and more libraries. So what should have been simple bugfix update turned into need for major update of 1 package and 2 new package additions. If this update contained security fixes it would cause serious problems to resolve in timely manner.

Summary

  • Create source releases containing build scripts
  • Think about your dependencies carefully
  • Handle micro releases gracefully

Next time I’ll look into some Ant and Maven specifics that are causing problems for packagers and how to resolve them in your projects.

Problems with running gpg-agent as root

February 14, 2011 in bug, fedora, howto, problem, security

This is gonna be short post for people experiencing various issues with pinentry and gpg-agent. This is mostly happening on systems with only gpgv2.

I have been asked to look at bug 676034 in Red Hat Enterprise Linux. There we actually two issues there:

  • Running pinentry with DISPLAY variable set but no available GUI pinenty helpers
  • Using gpg on console after doing “su -”

First problem was relatively easy to figure out. Pinentry finds DISPLAY variable and looks for pinentry-gtk, pinentry-qt or pinentry-qt4 helpers to ask for passphrase. Unfortunately if none of these GUI helpers can be found, pinentry doesn’t try their console counterpart. Workaround is simple: unset DISPLAY variable if you are working over ssh connection (or don’t use X forwarding when you don’t need it). More recent pinentry features proper failover to pinentry-curses

Second problem was a bit more tricky to figure out, although in the end it was a facepalm situation. When trying to use GNUPG as root on console, hoping for pinentry-curses to ask for passphrase, users were instead introduced to this message: ERR 83886179 Operation cancelled. To make things more confusing, everything seemed to work when logging in as root directly from ssh.

At first I thought that this must be caused by environment variables, but this seemed to be incorrect assumption. Instead the reason was that current tty was owned by original owner and not root. This seemed to cause problem with gpg-agent and/or ncurses pinentry. I will investigate who was the real culprit here, but this bug seems to be fixed at least in recent Fedoras

So what should you do if you have weird problems with gpg and pinentry as root? Here’s what:


$ su -
[enter password]
# chown root `tty`
[use gpg, pinentry as you want]

Easy right? As a final note…I’ve been to FOSDEM and I plan to blog about it, but I guess I am waiting for the videos to show online. It’s quite possible I’ll blog about it before that however, since it’s taking a while.

Fedora has Freemind

November 30, 2010 in fedora, packaging, software

During past few months I have been reviewing packages for Fedora with approximate speed of 1.53 package per week :-)

Most of packages I reviewed were libraries and other things that are not so interesting to users. But one of last packages I reviewed is different. It is one of the best mind-mappingsoftware in existence :-) Yes, it’s Freemind. If you’ve never tried mind-mapping before, let me quote first paragraph from wikipedia:

A mind map is a diagram used to represent words, ideas, tasks, or other items linked to and arranged around a central key word or idea. Mind maps are used to generate, visualize, structure, and classify ideas, and as an aid to studying and organizing information, solving problems, making decisions, and writing.

So what are you waiting for? Try it out!/>/> There were attempts to package Freemind before, but all would-be maintainers gave up when they noticed how many dependencies are needed and how Java packaging actually works (I don’t really blame them). So everyone please. Let’s. Have. A. Staaaaanding. Ovaaation. Fooor. Johannes Lips. He made it! If you live close by, buy him a beer will you? :-)

PyQTrailer revisited

November 10, 2010 in en, fedora, open source, projects, pyqt, python, software

Some time ago, I wrote about my little project: apple.com trailer downloader. Apple is still not very open-source friendly as far as its trailer website is concerned. So all points I made in my original post still stand. To my surprise this little project is still alive and kicking, with new ideas for improvements coming and coming :-). What is even more important: it seems that so far no breakage happened due to apple changing something on the web.

Since the first version I released almost 6 months ago several new features appeared. Some of them include:

  • Parallel downloading of trailers
  • Ability to run movie player (mplayer, vlc, etc) without downloading file to HDD
  • Lot of customisation/performance options added
  • Working support for trailer search
  • Localisation support
  • Python 3 support

Latest version (0.5.2) is available in Gentoo repositories already, and should hit Fedora updates in next day or so (this will be delayed due to new package acceptance criteria though). Enjoy.

Fedora RPG – Three level badge system?

October 20, 2010 in fedora, game, open source, rant

I stumbled upon one great idea on Fedora Planet. It is nothing other than Fedora RPG!

In short, it’s a system to create characters similar as they are in Role-playing games (RPGs) with levels, skill points and more.

You might think it doesn’t make sense to give contributors “points” for non-gaming activities but you would be wrong. Most communities have created ways to reward their members this way. Look no further than my favourite stackoverflow.com. It also uses badge and skill point system for various actions on the website. In one of earliest blog posts about how stackoverflow will work, Jeff Atwood shared his vision: three levels of badges (bronze, silver, gold). Each level with unique badges tailored to the purpose of stackoverflow.

I guess Fedora RPG will go a bit further in this regard. I would love to know how it will all turn out and how the levels will work. Let the games begin!

Packaging workflow, patch management and git magic in Fedoraland

October 15, 2010 in en, fedora, git, howto, linux, packaging

Big part of my job is packaging for Fedora Linux (I am pretty sure I haven’t mentioned this before :-) ). I have spent last 6 months working on various Java packages, adding new packages to Fedora, updating dependencies etc. I have developed certain workflow which I believe might be of interest to other packagers. So here goes. Most of these hints are about managing patches for your packages. I’ll also try to work on concrete package so it won’t be completely theoretical.

Let’s assume your project already has some history and patches. Let’s fix velocity bug 640660 for example. I’ll start with steps I took and what they meant, and I’ll summarize in the end with rationale what I have gained by using my workflow (and what could be improved).

After modifying BuildRequires and Requires to tomcat6 servlet api I tried to build velocity:

$ fedpkg mock

This is what I got:

---snip----
compile-test:
[javac] Compiling 125 source files to /builddir/build/BUILD/velocity-1.6.3/bin/test-classes
[javac] /builddir/build/BUILD/velocity-1.6.3/bin/test-src/org/apache/velocity/test/VelocityServletTestCase.java:135: org.apache.velocity.test.VelocityServletTestCase.MockServletContext is not abstract and does not override abstract method getContextPath() in javax.servlet.ServletContext
[javac] static class MockServletContext implements ServletContext
[javac] ^
[javac] Note: /builddir/build/BUILD/velocity-1.6.3/bin/test-src/org/apache/velocity/test/VelocityServletTestCase.java uses or overrides a deprecated API.
[javac] Note: Recompile with -Xlint:deprecation for details.
[javac] Note: Some input files use unchecked or unsafe operations.
[javac] Note: Recompile with -Xlint:unchecked for details.
[javac] 1 error
BUILD FAILED
/builddir/build/BUILD/velocity-1.6.3/build/build.xml:251: Compile failed; see the compiler error output for details.
Total time: 47 seconds
---snip---

The issue seems simple to fix, just missing stub function in a test case, right? So what now?

$ fedpkg prep
$ mv velocity-1.6.3 velocity-1.6.3.git
$ cd velocity-1.6.3.git
$ git init && git add . && git commit -m 'init'

This effectively created my small git repository for sources and populated it with all files. Using fedpkg prep step we extracted the tarball and applied already existing patches to unpacked sources. I suggest you create shell alias for last three commands as you’ll be using it a lot. We moved directory to velocity-1.6.3.git so that next (accidental?) fedpkg prep won’t erase our complicated changes (yes it happened to me once. I’ve had better days). Note that velocity-1.6.3.git is not a temporary directory. I will keep it around after fixing this bug so that I can use git history, diffs and other features in the future. It is especially nice when you have packages with lot of patches on top.

Now we can easily work in our new git repository, edit source file in question and do:

$ git add src/test/org/apache/velocity/test/VelocityServletTestCase.java
$ git commit -m 'Fix test for servlet api 2.5'
$ git format-patch HEAD~1

This created commit with descriptive message and generated a patch file 0001-Fix-test-for-servlet-api-2.5.patch in our current directory. This is how the patch looks like:

From 8758e3c83411ffadc084d241217fc25f1fd31f42 Mon Sep 17 00:00:00 2001
From: Stanislav Ochotnicky
Date: Thu, 14 Oct 2010 10:20:52 +0200
Subject: [PATCH] Fix test for servlet api 2.5

---
.../velocity/test/VelocityServletTestCase.java | 7 ++++++-
1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/src/test/org/apache/velocity/test/VelocityServletTestCase.java b/src/test/org/apache/velocity/test/VelocityServletTestCase.java
index 824583e..ac0ab5c 100644
--- a/src/test/org/apache/velocity/test/VelocityServletTestCase.java
+++ b/src/test/org/apache/velocity/test/VelocityServletTestCase.java
@@ -16,7 +16,7 @@ package org.apache.velocity.test;
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
- * under the License.
+ * under the License.
*/

import java.io.IOException;
@@ -149,6 +149,11 @@ public class VelocityServletTestCase extends TestCase
return this;
}

+ public String getContextPath()
+ {
+ return "";
+ }
+
public String getServletContextName()
{
return "VelocityTestContext";
--
1.7.2.3

Now that we have patch prepared for velocity we need to use it in the spec file and we’re done.

Let’s say our first attempted patch wouldn’t work as expected and build (or test) still failed. We modify the sources again and do another commit. What we have now is:

$ git log --format=oneline
c15f7e02eaae93b755cc0bfde6def3d6e67d2b0f (HEAD, master) Fix previous commit
3e3d654c142c7028c9c7895579fba204c4c4bf08 Fix test for servlet api 2.5
2f32554ddf892f4cca3f78b1f82a7c3ab169c357 init

We don’t want two patches in the spec file for one fix so: time for git magic. You’ve probably heard of git rebase if you’ve been using git for a while. What we want to do now is merge last two commits into one, or in git-speak “squash” them. To do this you have to do:

$ git rebase -i HEAD~2

Now your editor should pop-up with this text:

pick 3e3d654 Fix test for servlet api 2.5
pick c15f7e0 Fix previous commit

# Rebase 2f32554..c15f7e0 onto 2f32554
#
# Commands:
# p, pick = use commit
# r, reword = use commit, but edit the commit message
# e, edit = use commit, but stop for amending
# s, squash = use commit, but meld into previous commit
# f, fixup = like "squash", but discard this commit's log message
#
# If you remove a line here THAT COMMIT WILL BE LOST.
# However, if you remove everything, the rebase will be aborted.
#

So we just need to change “pick c15f7e0 Fix previous commit” into “squash c15f7e0 Fix previous commit” (you can also use just ‘s’ instead of ‘squash’). Save. Close. Another editor window will open with something like this:

# This is a combination of 2 commits.
# The first commit's message is:

Fix test for servlet api 2.5

# This is the 2nd commit message:

Fix previous commit

# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.

For this case we will delete second message because we just want to pretend our first attempt was perfect :-). Save. Close. Now we have:

$ git log --format=oneline
cbabb6ac43f7bdb8e52ccd09c25cfd0a032b553c (HEAD, master) Fix test for servlet api 2.5
2f32554ddf892f4cca3f78b1f82a7c3ab169c357 init

Repeat as many times as you want. You can also re-order commits and change commit messages with rebase (note that if you just want to change last commit message you can do “git commit –amend”). I generally don’t create commits until I have working patch though.

So why do I think all this mumbo-jumbo improves my workflow? Let’s see:

  • I can have long comments for every patch I create (instead a line or two in spec file)
  • I can use the same patches to send directly to upstream
  • I don’t have to juggle around with diff and remember what files I changed where
  • Probably several other things I haven’t even realized

I have a few things that bother me of course. git format-patch generates filenames that are different from standard practice of %{name}-%{version}-message.patch. This is not a git problem. For packages where only my patches exist I stick with git naming, but when there are different patches I stick with naming they started. Another thing that is bothering me is that creating initial repository by using “fedpkg prep” hides patches that were applied to sources. That’s why I am thinking about re-working my packages so that all patches will be in my git repositories as commits with descriptive messages. No need for comments in the spec file anymore. Perhaps someone can suggest other improvements to my approach.