.. _tutorial_first_project:

Your first project
==================
To get a feel for the basics, we'll start with the most basic BuildStream project we
could think of.

.. note::

   This example is distributed with BuildStream
   in the `doc/examples/first-project
   <https://gitlab.com/BuildStream/buildstream/tree/master/doc/examples/first-project>`_
   subdirectory.


Creating the project
--------------------
First, lets create the project itself using the convenience :ref:`bst init <invoking_init>`
command to create a little project structure:

.. raw:: html
   :file: ../sessions/first-project-init.html


This will give you a :ref:`project.conf <projectconf>` which will look like this:

``project.conf``
~~~~~~~~~~~~~~~~

.. literalinclude:: ../../examples/first-project/project.conf
   :language: yaml

The :ref:`project.conf <projectconf>` is a central point of configuration
for your BuildStream project.


Add some content
----------------
BuildStream processes directory trees as input and output,
so let's just create a ``hello.world`` file for the project
to have.

.. raw:: html
   :file: ../sessions/first-project-touch.html


Declare the element
-------------------
Here we're going to declare a simple :mod:`import <elements.import>` element
which will import the ``hello.world`` file we've created in the previous step.

Create ``elements/hello.bst`` with the following content:


``elements/hello.bst``
~~~~~~~~~~~~~~~~~~~~~~

.. literalinclude:: ../../examples/first-project/elements/hello.bst
   :language: yaml


The source
~~~~~~~~~~
The :mod:`local <sources.local>` source used by the ``hello.bst`` element,
can be used to access files or directories which are stored in the same repository
as your BuildStream project. The ``hello.bst`` element uses the :mod:`local <sources.local>`
source to stage our local ``hello.world`` file.


The element
~~~~~~~~~~~
The :mod:`import <elements.import>` element can be used to simply add content
directly to the output artifacts. In this case, it simply takes the ``hello.world`` file
provided by it's source and stages it directly to the artifact output root.

.. tip::

   In this example so far we've used two plugins, the :mod:`local <sources.local>`
   source and the :mod:`import <elements.import>` element.

   You can always browse the documentation for all plugins in
   the :ref:`plugins section <plugins>` of the manual.


Build the element
-----------------
In order to carry out the activities of the :mod:`import <elements.import>` element
we've declared, we're going to have to ask BuildStream to *build*.

This process will collect all of the sources required for the specified ``hello.bst``
and get the backing :mod:`import <elements.import>` element to generate an *artifact*
for us.

.. raw:: html
   :file: ../sessions/first-project-build.html

Now the artifact is ready.

Using :ref:`bst show <invoking_show>`, we can observe that the artifact's state, which was reported
as ``buildable`` in the :ref:`bst build <invoking_build>` command above, has now changed to ``cached``:

.. raw:: html
   :file: ../sessions/first-project-show.html


Observe the output
------------------
Now that we've finished building, we can checkout the output of the
artifact we've created using :ref:`bst checkout <invoking_checkout>`

.. raw:: html
   :file: ../sessions/first-project-checkout.html

And observe that the file we expect is there:

.. raw:: html
   :file: ../sessions/first-project-ls.html


Summary
-------
In this section we've created our first BuildStream project from
scratch, but it doesnt do much.

We've observed the general structure of a BuildStream project,
and we've run our first build.