Bazel BUILD Files
External
Internal
Overview
A BUILD is a short program, an interpretable list of Starlark statements. It can be named BUILD or BUILD.bazel and where both exist, BUILD.bazel takes precedence.
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
When a build rule function is executed, it creates a new target in the graph, which can later referred using a label.
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.