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Packages

Build packages are defined in JSON files which can be found at:

Build packages are a Fuchsia-specific feature built on top of GN to help customize Fuchsia builds.

A build package file contains references to other build packages it expands on (imports) and the Fuchsia packages it adds to the build (packages):

{
    "imports": [
        "garnet/packages/prod/network”,
    ],
    "packages": [
        "//garnet/examples/http/wget"
    ]
}

Build packages define an aggregation of one or more build labels, either by importing other packages, or by referencing build labels. GN parses the JSON package definitions early on in the build (often referenced from product definitions, and those definitions determine what else GN has to do.

Fuchsia packages, not to be confused with build packages, are artifacts of the Fuchsia build system, generated by the GN targets listed in packages. A Fuchsia package includes a manifest of its contents, and zero or more executables and their assets.

For example, the above build packages file adds a Fuchsia package called "wget" to the build. This package contains the binaries built from the build target of the same name in //garnet/examples/http/wget/BUILD.gn:

package("wget") {
  deps = [
    # The path to the dependency that creates the wget binary.
    ":bin"
  ],
  binaries = [{
    name = "wget"
  }]
}

The binaries field in the package definition specifies that this package includes a single binary named wget. The binaries field does not create the binary--that's the job of the package's dependencies list, specified in deps:

# Executable defines a c++ binary, the label of the executable target will
# be the same as the name of the produced binary file.
executable("bin") {
  output_name = "wget"

  sources = [
    "wget.cc",
  ]

  deps = [
    # This executable also has its own dependencies.
    "//garnet/public/lib/app/cpp",
    "//garnet/public/lib/fidl/cpp",
  ]
}

The binaries field in a package target lets GN know to deploy the binary within Fuchsia when you boot your Fuchsia OS image, allowing you to run your binary from inside the Fuchsia shell:

$ wget google.com
--2018-06-13 17:04:44--  http://google.com/
$