buck-cells-example

This is an example of how Buck can be used with Git Submodules, rather than as a mono-repo build-system.

For this example, we are using LoopPerfect/neither, an Either implementation in C++ 14. The library is in a submodule at vendor/neither.

Build Instructions

First grab the submodules using:

git submodule update --init --recursive

Next, build the example with Buck:

buck run :example

What Problem Does Cells Solve?

Cells are a great fit for this situtation:

• You have a library in a repo that builds with Buck
• You want to use that library in your project
• You copy the library into your project but the library's BUCK files don't work, because the root (//) has changed to the root of your project
• You don't want to rewrite your library's BUCK files!

Cells allow us to create isolated sub-projects that have their own .buckconfig and their own Buck target heirarchy. Cells can use targets from other cells when those targets are exported.

How Does it Work?

The meat of the example is in .buckconfig:

[repositories]
  neither = vendor/neither

The repositories tag tells Buck where each cell lives in your project's folder structure. Each cell has an alias. Here we have neither = vendor/neither, which means the subfolder vendor/neither is a cell with the name neither.

We can refer to targets inside of a cell using this syntax: cell-name//:target-in-cell.

So to make our example target depend on LoopPerfect/neither:

deps = [
  'neither//:neither',
],

This is a really powerful feature, because it makes a library's BUCK files portable. All you need to do to expose a target inside of a cell is to make it public:

visibility = [
  'PUBLIC',
]

If you have a complex dependency graph, or if you just want something more convenient, you should consider using Buckaroo. Buckaroo will flatten your dependency graph, fetch source-code and write the appropriate repositories tags.