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+.. _mach_settings:
+
+========
+Settings
+========
+
+Mach can read settings in from a set of configuration files. These
+configuration files are either named ``machrc`` or ``.machrc`` and
+are specified by the bootstrap script. In mozilla-central, these files
+can live in ``~/.mozbuild`` and/or ``topsrcdir``.
+
+Settings can be specified anywhere, and used both by mach core or
+individual commands.
+
+
+Core Settings
+=============
+
+These settings are implemented by mach core.
+
+* alias - Create a command alias. This is useful if you want to alias a command to something else, optionally including some defaults. It can either be used to create an entire new command, or provide defaults for an existing one. For example:
+
+.. parsed-literal::
+
+    [alias]
+    mochitest = mochitest -f browser
+    browser-test = mochitest -f browser
+
+
+Defining Settings
+=================
+
+Settings need to be explicitly defined, along with their type,
+otherwise mach will throw when trying to access them.
+
+To define settings, use the :func:`~decorators.SettingsProvider`
+decorator in an existing mach command module. E.g:
+
+.. code-block:: python
+
+    from mach.decorators import SettingsProvider
+    from mozbuild.base import MachCommandBase
+
+    @SettingsProvider
+    class ArbitraryClassName(MachCommandBase):
+        config_settings = [
+            ('foo.bar', 'string', "A helpful description"),
+            ('foo.baz', 'int', "Another description", 0, {'choices': set([0,1,2])}),
+        ]
+
+``@SettingsProvider``'s must specify a variable called ``config_settings``
+that returns a list of tuples. Alternatively, it can specify a function
+called ``config_settings`` that returns a list of tuples.
+
+Each tuple is of the form:
+
+.. code-block:: python
+
+    ('<section>.<option>', '<type>', '<description>', default, extra)
+
+``type`` is a string and can be one of:
+string, boolean, int, pos_int, path
+
+``description`` is a string explaining how to define the settings and
+where they get used. Descriptions should ideally be multi-line paragraphs
+where the first line acts as a short description.
+
+``default`` is optional, and provides a default value in case none was
+specified by any of the configuration files.
+
+``extra`` is also optional and is a dict containing additional key/value
+pairs to add to the setting's metadata. The following keys may be specified
+in the ``extra`` dict:
+
+    * ``choices`` - A set of allowed values for the setting.
+
+Wildcards
+---------
+
+Sometimes a section should allow arbitrarily defined options from the user, such
+as the ``alias`` section mentioned above. To define a section like this, use ``*``
+as the option name. For example:
+
+.. parsed-literal::
+
+    ('foo.*', 'string', 'desc')
+
+This allows configuration files like this:
+
+.. parsed-literal::
+
+    [foo]
+    arbitrary1 = some string
+    arbitrary2 = some other string
+
+
+Finding Settings
+================
+
+You can see which settings are available as well as their description and
+expected values by running:
+
+.. parsed-literal::
+
+    ./mach settings  # or
+    ./mach settings --list
+
+
+Accessing Settings
+==================
+
+Now that the settings are defined and documented, they're accessible from
+individual mach commands from the mach command context.
+For example:
+
+.. code-block:: python
+
+    from mach.decorators import (
+        Command,
+        SettingsProvider,
+    )
+    from mozbuild.base import MachCommandBase
+
+    @SettingsProvider
+    class ExampleSettings(object):
+        config_settings = [
+            ('a.b', 'string', 'desc', 'default'),
+            ('foo.bar', 'string', 'desc',),
+            ('foo.baz', 'int', 'desc', 0, {'choices': set([0,1,2])}),
+        ]
+
+    @Command('command', category='misc',
+             description='Prints a setting')
+    def command(command_context):
+        settings = command_context._mach_context.settings
+        print(settings.a.b)
+        for option in settings.foo:
+            print(settings.foo[option])