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Taskcluster Mach commands
A number of mach subcommands are available aside from ``mach taskgraph
decision`` to make this complex system more accessible to those trying to
understand or modify it. They allow you to run portions of the
graph-generation process and output the results.
``mach taskgraph tasks``
Get the full task set
``mach taskgraph full``
Get the full task graph
``mach taskgraph target``
Get the target task set
``mach taskgraph target-graph``
Get the target task graph
``mach taskgraph optimized``
Get the optimized task graph
``mach taskgraph morphed``
Get the morphed task graph
See :doc:`how-tos` for further practical tips on debugging task-graph mechanics
Each of these commands takes an optional ``--parameters`` argument giving a file
with parameters to guide the graph generation. The decision task helpfully
produces such a file on every run, and that is generally the easiest way to get
a parameter file. The parameter keys and values are described in
:doc:`parameters`; using that information, you may modify an existing
``parameters.yml`` or create your own. The ``--parameters`` option can also
take the following forms:
Fetch the parameters from the latest push on that project
Fetch the parameters from the given decision task id
If not specified, parameters will default to ``project=mozilla-central``.
Taskgraph JSON Format
By default, the above commands will only output a list of tasks. Use `-J` flag
to output full task definitions. For example:
.. code-block:: shell
$ ./mach taskgraph optimized -J
Task graphs -- both the graph artifacts produced by the decision task and those
output by the ``--json`` option to the ``mach taskgraph`` commands -- are JSON
objects, keyed by label, or for optimized task graphs, by taskId. For
convenience, the decision task also writes out ``label-to-taskid.json``
containing a mapping from label to taskId. Each task in the graph is
represented as a JSON object.
Each task has the following properties:
The name of this task's kind
The task's taskId (only for optimized task graphs)
The task's label
The task's attributes
The task's in-graph dependencies, represented as an object mapping
dependency name to label (or to taskId for optimized task graphs)
The optimizations to be applied to this task
The task's TaskCluster task definition.
The results from each command are in the same format, but with some differences
in the content:
* The ``tasks`` and ``target`` subcommands both return graphs with no edges.
That is, just collections of tasks without any dependencies indicated.
* The ``optimized`` subcommand returns tasks that have been assigned taskIds.
The dependencies array, too, contains taskIds instead of labels, with
dependencies on optimized tasks omitted. However, the ``task.dependencies``
array is populated with the full list of dependency taskIds. All task
references are resolved in the optimized graph.
The output of the ``mach taskgraph`` commands are suitable for processing with
the `jq <>`_ utility. For example, to extract all
tasks' labels and their dependencies:
.. code-block:: shell
jq 'to_entries | map({label: .value.label, dependencies: .value.dependencies})'
An alternate way of searching the output of ``mach taskgraph`` is
`gron <>`_, which converts json into a format
that's easily searched with ``grep``
.. code-block:: shell
gron taskgraph.json | grep -E 'test.*machine.platform = "linux64";'
./mach taskgraph --json | gron | grep ...
Diffing Taskgraphs
A common use case for running ``./mach taskgraph`` is to examine what changed
in the taskgraph from one revision to the next. The ``--diff`` flag can
facilitate this by automatically updating to the base revision of your stack
(or a specified revision) and generating the taskgraph there. It will then
update back to the current revision, generate the taskgraph again and produce a
diff of the two. It can work with both labels and JSON (``-J``). All flags
(such as ``--target-kind``, ``--parameters`` or ``--target-tasks-filter``) will
apply to both graphs so can therefore be used in conjunction with ``--diff``.
For example:
.. code-block:: shell
./mach taskgraph target --target-kind test --fast -J --diff
The above will display a diff of the current taskgraph compared to the base
revision of your stack. To compare against arbitrary revisions you can use
``--diff <specifier>``. E.g:
.. code-block:: shell
./mach taskgraph target --diff .~1 # hg
./mach taskgraph target --dif HEAD~1 # git
The command used to perform the diff can be set via the ``taskgraph.diffcmd`` setting. For example, add the following to your ``~/.mozbuild/machrc`` file:
.. code-block:: ini
diffcmd = diff --side-by-side