Subcommands of fx are defined in several directories:
//tools/devshell contains core scripts that are part of fx workflow.
//tools/devshell/contrib contains scripts that have been contributed by project members that have other levels of support, ownership, or both. The OWNERS file in the contrib directory provides a pointer to the individuals supporting the scripts there.
//vendor/*/scripts/devshell contains scripts that are relevant only to the particular vendor and will have an ownership and support model documented there.
Subcommands can be implemented in a number of languages, but it is recommended to use bash at this time, so as to be able to consume some of the helpers provided by //tools/devshell/lib/vars.sh.
It is recommended that scripts be kept short and simple. Authoring large shell programs without a significant test plan can lead to hard to maintain tools. If there is a need to produce a more sophisticated program the recommended approach is to author a host tool program as part of the regular Fuchsia build, and only to wrap that program in a very slim way in a script. Examples of such cases can be found in fx pave and fx make-fuchsia-vol. A good rule of thumb here is that if a script only needs to launch and manage a one or a few sub-processes, then shell may be a fine language. If the program needs to perform any significant string manipulation or business logic, it is likely better authored in a language that provides more structural capabilities and standard library.
Most subcommands start with a pre-amble of this nature (paths vary slightly):
source "$(cd "$(dirname "${BASH_SOURCE[0]}")" >/dev/null 2>&1 && pwd)"/../lib/vars.sh || exit $?
fx-config-read
This pre-amble ensures that the devshell helpers are loaded, and then reads the active fx configuration from the user-selected Fuchsia build directory.
fx-config-read is required for most environment variables to be set, and is necessary for most scripts.
fx-config-read loads the current user configuration that is either defined by the fx configuration modulated by fx set and fx use, or by flags to fx such as --config and --dir. It is necessary as a pre-amble for any script that wants to consume build artifacts, as it defined most of the standard environment variables such as $FUCHSIA_BUILD_DIR.
fx-error and fx-warn simply print their arguments, prefixing them with ERROR: or WARNING: respectively. If the output stream supports color, then these outputs are colored.
fx-command-run and fx-command-exec execute another fx subcommand, for example, running fx-command-run shell will invoke the fx shell command. The run variant executes the subcommand in a subshell and the exec variant execs the subcommand, replacing the calling process.
fx-command-help prints the command output for the currently running subcommand.
TODO(raggi): rename the following two functions:
get-device-name returns either the device name that the user has set with fx set-device or fx -d <device-name>. If the user has not set a default device, the command will run device discovery, and will return a discovered device name provided there is only one device discovered.
get-fuchsia-device-addr consumes get-device-name and returns the Fuchsia IPv6 address of the device. The returned address is the “netstack address”, not the “netsvc address”.
The vars.sh script may define additional functions, however, they are considered internal and may change more often. Users can request additional helper functions by contacting the devshell owners, or by defining their own library scripts in contrib.
After a successful invocation of fx-config-read in a script, one would observe the following environment variables:
FUCHSIA_ARCH - The current architecture selected (currently one of x64/arm64) FUCHSIA_BUILD_DIR - The path to the current Fuchsia build directory FUCHSIA_DIR - The path to the root of the Fuchsia source tree FUCHSIA_OUT_DIR - (deprecated) "$FUCHSIA_DIR/out" ZIRCON_BUILDROOT - The path to the Zircon build directory ZIRCON_TOOLS_DIR - The path to the Zircon host-tools build directory.
fx-config-read and/or fx could set additional environment variables, but users should not rely on them - only the above list are to be preserved (unless marked deprecated).
As many fx subcommands delegate to sub-programs passing on flags directly to them, it is prohibitive to always be able to respond to the -h or --help flags. As such fx subcommands SHOULD implement -h and --help if possible, but this is not required.
It is required that all subcommands implement help documentation lines, which are defined as follows:
#### CATEGORY=Category name ### a short one-line (<70 character) description for the command lines ## usage: fx <subcommand> [-a|-b|-c] --foo ... ## ## Long descriptions, flags, and so on
The first line starting with ### is consumed by fx help to produce a list of subcommands with one-line descriptions of what the subcommand does. These lines should be kept short so as to render well under fx help.
Lines starting with ## are output when a user invokes fx help subcommand, and are used to provide full subcommand help output. The long form output should document all flags and provide fuller description of the subcommand behaviors as appropriate.
Lines starting with #### contain metadata. The following metadata fields are supported:
#### CATEGORY=Category: the subcommand is grouped under the specified category in the output of fx help. There's no enforcement on the name of the category, but whenever possible it should be one of the existing categories.
#### DEPRECATED: deprecated subcommands are not listed by default on fx help.
Where possible, a subcommand can use fx-command-help to print out the long-form help (defined by ## lines). Many subcommands implement -h and --help to invoke fx-command-help and this is recommended.
When subcommands are scripts, documentation is embedded as comments in the scripts themselves. However, that's not always possible, for example for binaries produced by the build, such as fidldoc, prebuilt binaries like gn and symlinks like rustdoc and gen-cargo. In any case where metadata cannot be in the subcommand itself, fx looks for a metadata file with the .fx extension in the same directories where it looks for subcommands. If such a file exists, it represents a subcommand with the same name without the .fx extension.
<subcommand>.fx files follow the same format described in the previous section, with an optional metadata field:
#### EXECUTABLE=location_of_executable: points to the actual executable, which can be anywhere in the tree or in the build output. It can/must use the following variables to refer to known paths:
${FUCHSIA_DIR}: root of the Fuchsia source tree${PREBUILT_3P_DIR}: location of the 3p prebuilts (usually ${FUCHSIA_DIR}/prebuilt/third_party)${HOST_PLATFORM}: platform of the host, used to compose prebuilt paths${HOST_TOOLS_DIR}: path of the host tools produced by the buildSome examples of valid uses of EXECUTABLE in .fx files:
#### EXECUTABLE=${FUCHSIA_DIR}/.jiri_root/bin/cipd#### EXECUTABLE=${PREBUILT_3P_DIR}/gn/${HOST_PLATFORM}/gn#### EXECUTABLE=${FUCHSIA_DIR}/.jiri_root/bin/jiri#### EXECUTABLE=${PREBUILT_3P_DIR}/ninja/${HOST_PLATFORM}/ninjaSubcommands that are shell scripts should be tested using the Bash test framework in //tools/devshell/tests/lib/bash_test_framework.sh, which provides facilities for mocking components and encapsulating the execution context in a temporary directory without any impact on the working tree.
Each test suite with one or more tests is a Bash script which name ends with _test in a subdirectory of //tools/devshell/tests.
To run shell tests, execute fx self-test <tests_script>. To find out what test scripts are available, run fx self-test without arguments and they will be listed at the bottom. To run all the tests from all the test scripts, use --all. Other sample invocations are described below:
fx self-test --all # run all tests from all tests scripts fx self-test subcommands # run all tests scripts in //tools/devshell/tests/subcommands fx self-test subcommands/fx_set_test # run all tests in //tools/devshell/tests/subcommands/fx_set_test fx self-test fx-internal/fx_test # run all tests in //tools/devshell/tests/fx-internal/fx_test fx self-test fx-internal/fx_test --test TEST_fx-subcommand-run # run a single test from fx-internal/fx_test
To implement new shell test scripts, create a new file *_test in a subdirectory of //tools/devshell/tests using the Bash test framework documented in //tools/devshell/tests/lib/bash_test_framework.sh.
There are many examples in //tools/devshell/tests. The test framework is documented in the framework script.
Subcommands that are primarily non-shell, for example Rust or Dart, should have regular tests integrated with the Fuchsia build.
For example, the fx test subcommand is written in Dart and has tests defined in its BUILD.gn file.