Track changes through the history of PHP projects
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The Qafoo ChangeTrack tool allows you to track changes in classes and methods throughout the history of a PHP project. One application for this analysis is to detect artifacts that are changed most frequently and especially most frequently due to bugs.

Quick Start

To get started, download a recent release PHAR.

To create the base analysis file (changes by methods) try:

$ php changetrack.phar analyze -o analysis.xml -p

This will analyze the history of ChangeTrack itself, store the resulting XML in analysis.xml and display its progress to you.

On that basis, you can analyze bugfix/feature frequencies per method using:

$ php changetrack.phar calculate analysis.xml > label-frequency.xml

This will use the standard regex label-provider to assign change labels and calculate the frequency for each method.

Also on basis of the analysis.xml you can calculate frequent item sets among method changes, using:

$ php changetrack.phar frequent-item-sets -s 0.05 analysis.xml > fis.xml

That yields you a fis.xml with methods that are commonly changed together in 5% or more commits.

Please refer to the following sections for a deeper insight and to the commandline help commands.


The analysis is performed in multiples steps. Currently supported are:

  1. Analyze which classes/methods are affected by a revision.
  2. Analyze which classes/methods are most frequently affected by changes.
  3. Analyze which methods are commonly edited together.

The split into multiple steps allows you to

a) Cache the result of a step to apply multiple other analysis steps on top. b) Easily apply analysis processes which are currently not supported by ChangeTrack.

The different analysis types are combined in the single track shell command. Executing it using:

$ src/bin/track

Will provide you with a list of sub-commands to perform actual analysis.


To install the tool, download a PHAR release or obtain a checkout from Github, get Composer and execute:

$ composer install

After that, you can use ChangeTrack from src/bin/track.


In following, the currently implemented analysis commands are described in further detail.


The analyze command tracks changes of a PHP project throughout its version history (currently only Git is supported). The result is an XML document, that describes the version history in terms of class/method changes. For example, here is a part of the Twig project history:

<changes repository="">
  <!-- ... -->
  <changeSet revision="92bbc7ee405f5635f4647040d883dbd77d1ac7da" message="made a small optimization to for loop when no else clause exists&#10;git-svn-id: 93ef8e89-cb99-4229-a87c-7fa0fa45744b&#10;">
    <package name="">
      <class name="Twig_Node_For">
        <method name="compile">
  <!-- ... -->

Each revision (which contains a change to a class/method) is reflected in a <changeSet /> which gives you the version (hash) and the commit message. Contained is information about all method changes (structured by package and class name) and statistics on the number of added/removed lines.

You can restrict the history to be analyzed by a start and end commit through command line parameters. This makes some sense, since analysis is quite expensive: Every revision needs to be checked out and static analysis is performed to detect which artifacts are affected by the change.

The raw output of the analyze command is not really useful, yet. You should apply the calculate command to it.


The calculate command analyzes, how often an artifact (i.e. method) is affected by what kind of change (e.g. bug or feature). To do so, it attempts to assign a label to each commit in the project history and counts per method, how often a specifically labeled commit touched it. To do this, the calculate command operates on the output of the analyze command (either by specifying the input file as an argument on the shell or by just piping it from STDIN).

In order to find a label for a commit, calculate commonly analyzes the commit message for keywords (e.g. "implemented" or "fixed"), but can also utilize other methods (e.g. checking for a Github issue reference and looking up its assigned labels through the Github API). The label for a commit is then assigned to each artifact that was changed in that commit.

Since every project has a different style of crafting its commit messages, you can define how labels are determined through a dedicated config.yml file (-c option), for example. The default configuration (chosen if now -c option is present) looks like this:

        - regex:
            pattern: '(fixed)i'
            label:   'fix'
        - regex:
            pattern: '(implemented)i'
            label:   'implement'
        - default:
            label:   'misc'

This specific config.yml defines a chain of label providers. For a commit, each of the defined label providers (2 x regex, 1 x default) is asked to provide a label. If a provider can provide a label, this one is chosen.

The regex label provider tries to match pattern against the commit message and returns the defined label if it found a match. The default provider always returns the defined label and therefore finishes the chain.

An example output gathered using the default regex configuration (from above) for the Twig repository is shown below:

<stats  repository="">
  <package name="">
    <!-- ... -->
    <class name="Twig_Environment">
      <!-- ... -->
      <method name="loadTemplate">
          <count label="misc">17</count>
          <count label="fix">1</count>

As you can see, each method that occurrs in the history is listed together with the number of changes with a specific label. So, the calculate command found 17 commits with the label misc and 1 commit with the label fix for the method Twig_Environment::loadTemplate().

Besides the regex and default label providers, there's a Github issue label provider available, which uses your projects issue labels to determine a change label. An example configuration for vfsStream project looks like this:

        - github:
                bug:        bug
                feature:    feature
        - regex:
            pattern: '(implemented)i'
            label:   'feature'
        - regex:
            pattern: '(fix)i'
            label:   'bug'
        - regex:
            pattern: '(merged)i'
            label:   'merge'
        - default:
            label:   'misc'

The first provider in the chain tries to extract a Github issue reference (e.g. #23) from the commit message. If that is available, the Github API is used to determine labels for that issue. The labels provded by Github are then mapped to local labels (which are the same here).

If that provider does not find a label, 3 regexes are tried after each other. Finally, if none of the previous providers found a label, the default provider sets the misc label.


The frequent-item-sets command performs a Frequent Item Set Analysis, taking method changes as items and commits as transactions. That means, it calculates which methods are frequently edited together in your project.

The calculation is performed on basis of the results of the analysis command using:

$ track frequent-item-sets your_analysis_result.xml

The output of this command is an XML presenting all frequent item sets that could be found in your_analysis_result.xml, for example:

<?xml version="1.0" encoding="UTF-8"?>
    <!-- ... -->
    <itemSet support="0.011070110701107">
    <!-- ... -->

The example shows an extract with a single item set that consists of two items: The methods Twig_Node_Module::__construct() and Twig_Parser::parse() were edited together in more that 1% of the commits in the Twig repository.

You can apply the option -i to get a frequent item analysis on basis of classes instead of methods:

$ track frequent-item-sets -i class your_analysis_result.xml

Note that frequent item set analysis is typically applied to databases where the items do not change, which does not apply to software projects (e.g. new classes are created). Therefore, the typical setting of a high support value cannot hold here. Instead, in case of Twig 1% (0.01) is a sensible first support value to retrieve initial results.

The support value should be identified for each project individually. 0.5 is a good starting point, but most likely you need to go down to 0.1 or even 0.01. It can also make sense to only analyze a fraction of the changes (e.g. of the past year), if your project underwent a major refactoring.


The ChangeTrack tool is currently in a very early alpha state. It has only been run against a couple of repositories and it is expected that you find quite some bugs. However, here are some of the features which would make sense in the future:

  • Support different version control systems (e.g. SVN)
  • Performance improvements
  • Further label providers (e.g. by Jira issue labels)

Please add your ideas for additional features to the Github issue tracker and possibly provide a pull request.