build_defs.md

Build file format

The build files are very simple. There are no conditional or control flow statements.

Modules

A module starts with a module type followed by a set of properties in name: value format.

bob_binary {
    name: "less",
    srcs: ["src/less.c"],
    ldlibs: ["-lncurses"],
}

Every module has a name property that is unique.

Bob module types

Bob has a number of module types. The properties available in each module type are documented in the following pages.

• bob_alias
• bob_binary
• bob_defaults
• bob_external_header_library
• bob_external_shared_library
• bob_external_static_library
• bob_generate_binary
• bob_generate_shared_library
• bob_generate_source
• bob_generate_static_library
• bob_install_group
• bob_kernel_module
• bob_resource
• bob_shared_library
• bob_static_library
• bob_transform_source
• bob_genrule

Globs

Properties taking filenames also accept glob patterns. * is the normal Unix wildcard, so src/*.c would select all C files in the src directory. ** will match zero or more path elements, so src/**.c will match all C files in the src directory and its subdirectories.

Variables

Build files may contain top-level variable assignments:

less_srcs = ["src/less.c"]

bob_binary {
    name: "less",
    srcs: less_srcs,
    ldlibs: ["-lncurses"],
}

Before they are referenced, variables can be appended to with +=. After they have been referenced by a module they are immutable.

Comments

Comments use C-style multiline /* */ and C++ style single-line // formats.

Types

The type of a variable is determined by the assignment. The type of a property is determined by the module type.

• Bool (true or false)
• Integers
• Strings ("string")
• Lists of strings(["string1", "string2"])
• Maps ({ key1: "value1", key2: 10, key3: ["value3"] })

Maps may contain values of any type. Lists and maps may have trailing commas after the last value.

Strings can contain Go templates (except in the name, defaults, and flag_defaults properties). Go templates start with {{ and end with }}. Bob may expand Go templates more that once, which means that getting literal {{ or }} is implementation dependent.

Operators

Strings, lists of strings, and maps can be appended using the + operator.

Defaults

A defaults module can be used to repeat the same properties in multiple modules (currently restricted to the types bob_binary, bob_static_library, bob_shared_library and bob_kernel_module)

bob_defaults {
    name: "common_libs",
    ldlibs: ["-lncurses"],
}

bob_binary {
    name: "less",
    defaults: ["common_libs"],
    srcs: ["src/less.c"],
}

Defaults can name other defaults.

Features

In most module types, every boolean configuration item (feature) is a map property (lower cased). Within this map the standard module properties can be used. This appends the properties to the module when the feature is enabled.

bob_binary {
    name: "less",
    srcs: ["src/less.c"],
    ldlibs: ["-lncurses"],
    use_locales: {
        srcs: ["src/locales.c"],
    }
}

Features cannot nest. Instead of nesting, separate features should be used.

Referencing configuration values

Configuration values can be used within string properties via Go templates. As with features, the configuration identifier is lower cased.

bob_binary {
    name: "less",
    srcs: ["src/less.c"],
    ldlibs: ["-lncurses"],
    use_locales: {
        srcs: ["src/locales.c"],
        cflags: ["-DDEFAULT_LOCALE={{.default_locale}}"],
    }
}

Formatter

Bob includes a canonical formatter for blueprint files. To format a build file in place:

bpfmt -w build.bp

The canonical format uses 4 space indent, newlines after every element of a multi-element list, and always includes trailing commas.