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Build File

A build file is a file, typically named BUCK, that defines one or more build rules. Note that you can change the name that Buck2 uses for the build file in the buildfile section of .buckconfig. A source file in your project can only be referenced by rules in its "nearest" build file, where "nearest" means its closest direct ancestor in your project's file tree. (If a source file has a build file as a sibling, then that is its nearest ancestor.) For example, if your project had the following BUCK files:


Then your build rules would have the following constraints:

  • Rules in java/com/facebook/base/BUCK can reference any file under java/com/facebook/base/.
  • Rules in java/com/facebook/common/ can reference any files under that directory, except for those under java/com/facebook/common/collect/, as those "belong" to the BUCK file in the collect directory.

The set of source files accessible to a build file is also known as its build package. The way to refer to code across build packages is to create build rules and use deps to refer to that code. Going back to the previous example, suppose code in java/com/facebook/common/concurrent/ wants to depend on code in java/com/facebook/common/collect/. Presumably java/com/facebook/common/collect/BUCK has a build rule like:

name = 'collect',
srcs = glob(['*.java']),
deps = ['//java/com/facebook/base:base',],)

Then java/com/facebook/common/BUCK could have a rule like:

name = 'concurrent',
srcs = glob(['concurrent/*.java']),
deps = ['//java/com/facebook/base:base','//java/com/facebook/common/collect:collect',],)

whereas the following would be invalid because java/com/facebook/common/collect/ has its own build file, so //java/com/facebook/common/collect:concurrent cannot list java/com/facebook/common/collect/*.java in its srcs.

name = 'concurrent',
srcs = glob(['collect/*.java', 'concurrent/*.java']),
deps = ['//java/com/facebook/base:base',],)