This guide shows you how to build Fuchsia to include an example package from Fuchsia's source //examples directory and run that component on your Fuchsia device.
Note: This guide is specific to components v1 and uses component manifests.
Open the examples/hello_world/BUILD.gn file.
This example, written in both C++ and Rust, prints Hello, world!. Each language-dependent directory has the following:
BUILD.gn file that defines its Fuchsia package.meta subdirectory with component manifests (.cmx) files.Generate Ninja (GN) is a meta build system. Output files from GN serve as inputs to Ninja{:.external}, the actual build system. If you aren't familiar with GN, see Introduction to GN.
In the examples/hello_world/BUILD.gn file, the hello_world target is a group containing other dependencies, notably cpp and rust. Therefore, this target builds both of them:
group("hello_world") { testonly = true deps = [ ":tests", "cpp", "rust", ] }
To learn more about how GN defines Fuchsia packages, see the build/package.gni file.
A .cmx file, known as a component manifest, describes how to run an application on Fuchsia as a component. In other words, a component manifest creates a Fuchsia package.
To include a package in your Fuchsia image, you have the following options:
Base: Packages that are produced by build and included in paving images. These packages are included in over-the-air updates and are always updated as a single unit.
Cache: Packages that are included in paving images, but are not included in over-the-air system updates. These packages can be updated at any time when updates are available.
Universe: Packages that are not included in paving image. These optional packages are fetched and run on-demand.
Note: If you already built Fuchsia and you're not changing your product or board, these commands take less than a few minutes to run. If you are changing your product or board, these changes can take up to 90 minutes to run.
To include the example package in Universe so that it can be fetched on-demand, use the --with flag when setting your product and board environment and building Fuchsia:
For a Fuchsia emulator with the minimum build configuration, the command is:
fx set core.qemu-x64 --with //examples/hello_world
In this example, core is a product with a minimal feature set, which includes common network capabilities, and x64 refers to the x64 architecture.
For a Fuchsia device with the minimum build configuration, the command is:
fx set core.x64 --with //examples/hello_world
See Configure a build for more options.
Once you have set your build configuration, build Fuchsia with the following command:
fx build
You now have a build that includes the example package in Universe.
To run a Fuchsia component, use its Fuchsia package URL as an argument to the fx shell run command:
Open a terminal and run fx serve:
fx serve
Open another terminal and run the example component:
fx shell run fuchsia-pkg://fuchsia.com/hello_world_cpp#meta/hello_world_cpp.cmx
This command prints the following output:
Hello, World!
If fx serve is not running, the command prints an error message from the device or emulator.
If fx serve is running, but the package is not found, then try going through these steps again, rebuilding your Fuchsia image to include this package and repaving it to the device.
The fx shell run command can match a string to a package URL if the string is only mapped to one component in your product configuration. For example:
$ fx shell run hello_world_cpp.cmx
If multiple matches exist, the command prints the list of matches:
$ fx shell run hello_world fuchsia-pkg://fuchsia.com/hello_world_cpp_tests#meta/hello_world_cpp_unittests.cmx fuchsia-pkg://fuchsia.com/hello_world_cpp#meta/hello_world_cpp.cmx Error: "hello_world" matched multiple components.
You can explore what components are in your product configuration using the locate command.
Find your favorite component:
fx shell locate hello_world_cpp.cmx
Find all runnable components:
fx shell locate --list cmx
Find multiple test components:
fx shell locate --list test