Reblog of build visualization post

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+---
+layout: posts
+title: Visualize your build
+---
+
+_Reposted from
+[Kristina Chodorow's blog](http://www.kchodorow.com/blog/2015/04/24/have-you-ever-looked-at-your-build-i-mean-really-looked-at-your-build/)._
+
+Bazel lets you see a graph of your build dependencies.  It _could_ help you
+debug things, but honestly it's just really cool to see what your build is doing.
+
+To try it out, you'll need a project that uses Bazel to build.  If you don't
+have one handy,
+[here's a tiny workspace](https://github.com/kchodorow/tiny-workspace) you can
+use:
+
+```bash
+$ git clone https://github.com/kchodorow/tiny-workspace.git
+$ cd tiny-workspace
+```
+
+Make sure you've
+[downloaded and installed Bazel](http://bazel.io/docs/install.html) and have the
+following line to your _~/.bazelrc_:
+
+```
+query --package_path %workspace%:[path to bazel]/base_workspace
+```
+
+Now run `bazel query` in your _tiny-workspace/_ directory, asking it to search
+for all dependencies of `//:main` and format the output as a graph:
+
+```bash
+$ bazel query 'deps(//:main)' --output graph > graph.in
+```
+
+This creates a file called _graph.in_, which is a text representation of the
+build graph.  You can use `dot` (install with `sudo apt-get install graphviz`)
+to create a png from this:
+
+```bash
+$ dot -Tpng < graph.in > graph.png
+```
+
+If you open up _graph.png_, you should see something like this:
+
+<img src="/assets/graph.png">
+
+You can see `//:main` depends on one file (`//:main.cc`) and four targets
+(`//:x`, `//tools/cpp:stl`, `//tools/default:crosstool`, and
+`//tools/cpp:malloc`).  All of the `//tools` targets are implicit dependencies
+of any C++ target: every C++ build you do needs the right compiler, flags, and
+libraries available, but it crowds your result graph.  You can exclude these
+implicit dependencies by removing them from your query results:
+
+```bash
+$ bazel query --noimplicit_deps 'deps(//:main)' --output graph > simplified_graph.in
+```
+
+Now the resulting graph is just:
+
+<img src="/assets/simple-graph.png">
+
+Much neater!
+
+If you're interested in further refining your query, check out the
+[docs on querying](/docs/query.html).