stack-2.9.1: doc/dependency_visualization.md
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# Dependency visualization
You can use stack to visualize the dependencies between your packages and
optionally also external dependencies.
First, you need [Graphviz](https://www.graphviz.org/). You can [get it here](https://www.graphviz.org/download/).
As an example, let's look at `wreq`. Command:
~~~text
stack dot | dot -Tpng -o wreq.png
~~~
[](https://cloud.githubusercontent.com/assets/591567/8478591/ae10a418-20d2-11e5-8945-55246dcfac62.png)
Okay that is a little boring, let's also look at external dependencies. Command:
~~~text
stack dot --external | dot -Tpng -o wreq.png
~~~
[](https://cloud.githubusercontent.com/assets/591567/8478621/d247247e-20d2-11e5-993d-79096e382abd.png)
Well that is certainly a lot. As a start we can exclude `base` and then
depending on our needs we can either limit the depth. Command:
~~~text
stack dot --no-include-base --external --depth 1 | dot -Tpng -o wreq.png
~~~
[](https://cloud.githubusercontent.com/assets/591567/8484310/45b399a0-20f7-11e5-8068-031c2b352961.png)
or prune packages explicitly. Command:
~~~text
stack dot --external --prune base,lens,wreq-examples,http-client,aeson,tls,http-client-tls,exceptions | dot -Tpng -o wreq_pruned.png
~~~
[](https://cloud.githubusercontent.com/assets/591567/8478768/adbad280-20d3-11e5-9992-914dc24fe569.png)
Keep in mind that you can also save the dot file. Command:
~~~text
stack dot --external --depth 1 > wreq.dot
dot -Tpng -o wreq.png wreq.dot
~~~
and pass in options to `dot` or use another graph layout engine like `twopi`.
Command:
~~~text
stack dot --external --prune base,lens,wreq-examples,http-client,aeson,tls,http-client-tls,exceptions | twopi -Groot=wreq -Goverlap=false -Tpng -o wreq_pruned.png
~~~
[](https://cloud.githubusercontent.com/assets/591567/8495538/9fae1184-216e-11e5-9931-99e6147f8aed.png)
## Specifying local targets and flags
The `dot` and `list-dependencies` commands both also accept the following
options which affect how local packages are considered:
* `TARGET`, same as the targets passed to `build`
* `--test`, specifying that test components should be considered
* `--bench`, specifying that benchmark components should be considered
* `--flag`, specifying flags which may affect cabal file `build-depends`