Bazel BUILD Files
External
Internal
Overview
A BUILD is a short program, an interpretable list of Starlark statements. The BUILD file specified of how the files of a Bazel package can be used to produce artifacts. The BUILD file resides in the package directory.
The BUILD file can be named BUILD or BUILD.bazel and where both exist, BUILD.bazel takes precedence.
Relationship between BUILD File and Position in the Directory Tree
General Syntax
Variables must be defined before they are used.
The relative order in which build rules are declared is unimportant.
The file cannot contain function definitions, for or if control statements. List comprehensions and if expressions are allowed.
Starlark programs can't perform arbitrary I/O, which makes the interpretation of the BUILD files hermetic.
BUILD files need to be updated whenever the dependencies of the underlying code change. IntelliJ does that via the "Sync" functionality.
Build Rules
Reconcile with Bazel_Concepts#rules_go.
When a build rule function is executed, it creates a new target in the graph, which can later referred using a label.
The majority of build rules come in families, grouped together by language. For example, go_binary, go_library and cc_test are the build rules for Go binaries, libraries, and tests, respectively.
*_binary rules build executable in a given language. After a build, the executable will reside in the build tool's binary output tree at the corresponding name for the rule's label, so //my:program would appear at $(BINDIR)/my/program.
*_test rules are a specialization of a *_binary rule used for automated testing.
*_library rules specify separately-compiled modules in the given programming language.
Go Rules
go_library
go_binary
go_test
go_repository
Other Rules
Functions
Functions can be declared in .bzl files.
Extensions
Bazel extensions are files ending in .bzl. Symbols from an extension are imported with the load() statement:
load("//foo/bar:file.bzl", "some_library")
load("//meta/rules:go.bzl", "go_library")
load("//somewhere/gomock:defs.bzl", "gomock")
some_library(
...
)
go_library(
...
)
gomock(
...
)
This can be used to lad new build rules, functions or constants.