50 lines
1.9 KiB
ReStructuredText
50 lines
1.9 KiB
ReStructuredText
Task Definition YAML Templates
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==============================
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A few kinds of tasks are described using templated YAML files. These files
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allow some limited forms of inheritance and template substitution as well as
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the usual YAML features, as described below.
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Please do not use these features in new kinds. If you are tempted to use
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variable substitution over a YAML file to define tasks, please instead
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implement a new kind-specific transform to accopmlish your goal. For example,
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if the current push-id must be included as an argument in
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``task.payload.command``, write a transform function that makes that assignment
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while building a job description, rather than parameterizing that value in the
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input to the transforms.
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Inheritance
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-----------
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One YAML file can "inherit" from another by including a top-level ``$inherits``
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key. That key specifies the parent file in ``from``, and optionally a
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collection of variables in ``variables``. For example:
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.. code-block:: yaml
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$inherits:
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from: 'tasks/builds/base_linux32.yml'
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variables:
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build_name: 'linux32'
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build_type: 'dbg'
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Inheritance proceeds as follows: First, the child document has its template
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substitutions performed and is parsed as YAML. Then, the parent document is
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parsed, with substitutions specified by ``variables`` added to the template
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substitutions. Finally, the child document is merged with the parent.
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To merge two JSON objects (dictionaries), each value is merged individually.
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Lists are merged by concatenating the lists from the parent and child
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documents. Atomic values (strings, numbers, etc.) are merged by preferring the
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child document's value.
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Substitution
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------------
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Each document is expanded using the PyStache template engine before it is
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parsed as YAML. The parameters for this expansion are specific to the task
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kind.
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Simple value substitution looks like ``{{variable}}``. Function calls look
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like ``{{#function}}argument{{/function}}``.
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