Soong

Soong is the replacement for the old Android make-based build system. It replaces Android.mk files with Android.bp files, which are JSON-like simple declarative descriptions of modules to build.

Soong是google用来替代过去的Android构建系统的新一代构建系统，用JSON风格的Android.bp取代Android.mk。

Android.bp file format

By design, Android.bp files are very simple. There are no conditionals or control flow statements - any complexity is handled in build logic written in Go. The syntax and semantics of Android.bp files are intentionally similar to Bazel BUILD files when possible.

Android.bp文件设计上非常简洁，它不包含条件控制，将构建过程中所有复杂性都写在了Go中。bp文件的语法和语义被有意设计的和Bazel一致。

Modules

A module in an Android.bp file starts with a module type, followed by a set of properties in name: value, format:

Android.bp文件由一个模块类别起头，模块类别下定义了一系列由name：value表示的属性：

cc_binary {

name: "gzip",

srcs: ["src/test/minigzip.c"],

shared_libs: ["libz"],

stl: "none",

}

Every module must have a name property, and the value must be unique across all Android.bp files.

每个模块都有一个name属性，该属性必需在所有Android.bp文件中是唯一的。

For a list of valid module types and their properties see $OUT_DIR/soong/.bootstrap/docs/soong_build.html.

要了解所有可用的模块类别及支持的属性，可以构建AOSP，然后查询相关文档， $OUT_DIR/soong/.bootstrap/docs/soong_build.html.。

Variables

An Android.bp file may contain top-level variable assignments:

bp文件可以包含全局变量：

gzip_srcs = ["src/test/minigzip.c"],

cc_binary {

name: "gzip",

srcs: gzip_srcs,

shared_libs: ["libz"],

stl: "none",

}

Variables are scoped to the remainder of the file they are declared in, as well as any child blueprint files. Variables are immutable with one exception - they can be appended to with a += assignment, but only before they have been referenced.

变量在声明后，直到当前文件结束前都是有效的，包括子文件内也有效。变量在被使用前，可以使用 += 符号追加内容，一旦被引用过，变量就不可改变。

Comments

Android.bp files can contain C-style multiline /* */ and C++ style single-line // comments.

.bp文件中可以包含C风格的注释。

Types

Variables and properties are strongly typed, variables dynamically based on the first assignment, and properties statically by the module type. The supported types are:

变量和属性都是强类型的，变量在第一次被引用时确认类型，属性由所属的类别决定类型。以下为受支持的类型：

• Bool (true or false)
• Integers (int)
• Strings ("string")
• Lists of strings (["string1", "string2"])
• Maps ({key1: "value1", key2: ["value2"]})

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

Map的value可以是任意类型（注意到List似乎只能是String类型），也就是说value可以是嵌套的List或者Map。map和list的最后一个元素后面可以有一个额外的逗号。

Operators

Strings, lists of strings, and maps can be appended using the + operator. Integers can be summed up using the +operator. Appending a map produces the union of keys in both maps, appending the values of any keys that are present in both maps.

String、List和Map可以使用 + 运算符将内容合并到一起。整数可以用 + 运算符相加。对Map进行合并会对两个Map的key集合取并集，每个key对应的value是两个map中对应value的集合（这段不是很理解，待验证）。

Defaults modules

A defaults module can be used to repeat the same properties in multiple modules. For example:

默认模块可以包含公共的属性，被多个模块引用，避免重复，例如：

cc_defaults {

name: "gzip_defaults",

shared_libs: ["libz"],

stl: "none",

}

cc_binary {

name: "gzip",

defaults: ["gzip_defaults"],

srcs: ["src/test/minigzip.c"],

}

Name resolution

Soong provides the ability for modules in different directories to specify the same name, as long as each module is declared within a separate namespace. A namespace can be declared like this:

Soong可以让不同目录中的模块具有相同的名字，只要同名模块不在同一个namespace中。一个namespace的声明如下：

soong_namespace {

imports: ["path/to/otherNamespace1", "path/to/otherNamespace2"],

}

Each Soong module is assigned a namespace based on its location in the tree. Each Soong module is considered to be in the namespace defined by the soong_namespace found in an Android.bp in the current directory or closest ancestor directory, unless no such soong_namespace module is found, in which case the module is considered to be in the implicit root namespace.

每个Soong的模块都根据它所属的目录位置而被归为某一个namespace下。每个Soong的模块都属于距离所属目录层级最近的父目录所属的namespace，如果某个Soong模块无法被归为任何一个namespace，那它就被归于默认的root namespace。

When Soong attempts to resolve dependency D declared my module M in namespace N which imports namespaces I1, I2, I3..., then if D is a fully-qualified name of the form “//namespace:module”, only the specified namespace will be searched for the specified module name. Otherwise, Soong will first look for a module named D declared in namespace N. If that module does not exist, Soong will look for a module named D in namespaces I1, I2, I3... Lastly, Soong will look in the root namespace.

在Soong试图根据name找到某个module时，首先Soong会查看name是否已经指定了一个namespace，即name是否是”namespace:module”这样的形式，如果是，那么Soong就直接去指定的namespace寻找module；否则，Soong会挨个从当前文件引用的namespace查找module，最后再去root namespace查。

Until we have fully converted from Make to Soong, it will be necessary for the Make product config to specify a value of PRODUCT_SOONG_NAMESPACES. Its value should be a space-separated list of namespaces that Soong export to Make to be built by the m command. After we have fully converted from Make to Soong, the details of enabling namespaces could potentially change.

由于历史原因，现在AOSP还没有完全将构建系统从Make转换到Soong，因此在构建时必须要指定PRODUCT_SOONG_NAMESPACES环境变量，告诉Soong一个namespace列表。未来等AOSP完全迁移到Soong，可能会使用其他方式来指定namespace。

Formatter

Soong includes a canonical formatter for blueprint files, similar to gofmt. To recursively reformat all Android.bp files in the current directory:

bpfmt -w .

The canonical format includes 4 space indents, newlines after every element of a multi-element list, and always includes a trailing comma in lists and maps.

Convert Android.mk files

Soong includes a tool perform a first pass at converting Android.mk files to Android.bp files:

Soong提供了将Android.mk转换成Android.bp的工具：

androidmk Android.mk > Android.bp

The tool converts variables, modules, comments, and some conditionals, but any custom Makefile rules, complex conditionals or extra includes must be converted by hand.

这个工具仅能转换简单的Android.mk，如果Android.mk中包含条件控制等复杂成分，这个工具将无法转换。

Differences between Android.mk and Android.bp

• Android.mk files often have multiple modules with the same name (for example for static and shared version of a library, or for host and device versions). Android.bp files require unique names for every module, but a single module can be built in multiple variants, for example by adding host_supported: true. The androidmk converter will produce multiple conflicting modules, which must be resolved by hand to a single module with any differences inside target: { android: { }, host: { } } blocks.

Build logic

The build logic is written in Go using the blueprint framework. Build logic receives module definitions parsed into Go structures using reflection and produces build rules. The build rules are collected by blueprint and written to a ninjabuild file.

Other documentation

• Best Practices
• Build Performance
• Generating CLion Projects
• Make-specific documentation: build/make/README.md

FAQ

How do I write conditionals?

Soong deliberately does not support conditionals in Android.bp files. Instead, complexity in build rules that would require conditionals are handled in Go, where high level language features can be used and implicit dependencies introduced by conditionals can be tracked. Most conditionals are converted to a map property, where one of the values in the map will be selected and appended to the top level properties.

For example, to support architecture specific files:

cc_library {

...

srcs: ["generic.cpp"],

arch: {

    arm: {

        srcs: ["arm.cpp"],

    },

    x86: {

        srcs: ["x86.cpp"],

    },

},

}

See art/build/art.go or external/llvm/soong/llvm.go for examples of more complex conditionals on product variables or environment variables.

Contact

Email android-building@googlegroups.com (external) for any questions, or see go/soong (internal).