Introduction

This plugin for CocoaPods helps understand the dependencies between two pods. It is intended for projects with a large number of dependencies.

The plugin's output can be saved to YAML format for easy parsing by other tools (e.g. a CocoaPods GUI) or to GraphViz format for visualization.

Installation

Add this line to your application's Gemfile:

gem 'cocoapods-why'

And then run:

$ bundle

Or, install it system-wide with:

$ gem build cocoapods-why.gemspec
$ gem install cocoapods-why-1.0.0.gem

Or, in a single command:

$ bundle exec rake install

Usage

The plugin adds a why command to CocoaPods. You can get help on its parameters with:

$ pod why --help

All Paths Between Pods

The most common usage of the why command is to show all paths between two pods Foo and Bar:

$ pod why Foo Bar

This is helpful for understanding why a particular pod has a transitive dependency on some other pod (possibly one you do not want). By default, it simply lists the paths, but it can also produce a graph of them.

All Paths To A Pod

The why command can also show all pods that depend on some other pod, either directly or transitively.

$ pod why Foo

This is helpful for finding the set of pods that consume a particular pod and will have to be rebuilt (or could break) if it changes. By default, the command lists all of the pods, but it can also produce a graph of them.

Graphing

The why command can produce a graph of its output with the --to-dot argument, which takes a file name as a parameter. The output file will be in DOT format, which can be visualized with a DOT processor. For example, you can generate a PDF from a DOT file with this GraphViz command:

$ dot -Tpdf dependencies.dot > dependencies.pdf

Caching

Finding pods in the CocoaPods project can take a long time when there are many dependencies. To speed things up, the why command accepts a --cache parameter, which is used to specify a YAML file containing previous output from the query --to-yaml command (from the query plugin). When the plugin sees the --cache parameter, it will use the data in this file instead of rebuiding the data from the current CocoaPods instance.

This plugin was inspired by:

yarn why: It is similar to pod why but additionally provides information on the file sizes of the dependencies.
bazel query: Bazel offers a query language that can find the paths between two dependencies with bazel query "allpaths(...)" --graph.
dependencies: This CocoaPods plugin produces a graph of a single pod's dependencies.
graph: This CocoaPods plugin produces a wheel graph of all dependencies in a project.

Development

For local development of this plugin, the simplest approach is to install it into an existing app via absolute path. For example, if the code is in a directory called projects/cocoapods-why off the home directory, add the following line to the app's Gemfile:

gem 'cocoapods-why', path: "#{ENV['HOME']}/projects/cocoapods-why"

You can then make changes to the code and they will be executed when using the why command from the app's directory.