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A configuration option has:
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* a name: a valid python identifier (even if it's not used as an
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identifier in python itself)
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* a value: a unicode string or a list of unicode strings.
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The Option object is used to define its properties:
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* name: a name: a valid python identifier (even if it's not used as an
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identifier in python itself). This is also used to register the option.
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* default: the default value that Stack.get() should return if no
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value can be found for the option.
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* default_from_env: a list of environment variables. The first variable set
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will provide a default value overriding 'default' which remains the
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default value if *no* environment variable is set.
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* help: a doc string describing the option, the first line should be a
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summary and can be followed by a blank line and a more detailed
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* from_unicode: a callable accepting a unicode string and returning a
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suitable value for the option. If the string cannot be coerced it should
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* invalid: the action to be taken when an invalid value is encountered in a
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store (during a Stack.get()).
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Options are grouped into sections which share some properties with the well
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* the key is the name,
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* you can get, set and remove an option,
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* the value is a unicode string.
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MutableSection is needed to set or remove an option, ReadOnlySection should
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Options can be persistent in which case they are saved into Stores.
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``config.Store`` defines the abstract interface that all stores should
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This object doesn't provide direct access to the options, it only provides
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access to Sections. This is deliberate to ensure that sections can be
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properly shared by reusing the same underlying objects. Accessing options
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should be done via the ``Section`` objects.
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A ``Store`` can contain one or more sections, each section is uniquely
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identified by a unicode string.
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``config.ConfigObjStore`` is an implementation that use ``ConfigObj``.
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Depending on the object it is associated with (or not) a ``Store`` also needs
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to implement a locking mechanism. ``LockableConfigObjStore`` implements such a
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mechanism for ``ConfigObj`` based stores.
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Classes are provided for the usual Bazaar configuration files and could be
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used as examples to define new ones if needed. The associated tests provides a
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basis for new classes which only need to register themselves in the right
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places to inherit from the existing basic tests and add their own specific
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For some contexts, only some sections from a given store will apply. Defining
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which is what the ``SectionMatcher`` are about.
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The main constraint here is that a ``SectionMatcher`` should delay the loading
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of the associated store as long as possible. The constructor should collect
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all data needed for the selection and uses it while processing the sections in
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Only ``ReadOnlySection`` objects are manipulated here but a ``SectionMatcher``
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can return dedicated ``Section`` to provide additional context (the
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``LocationSection`` add an ``extra_path`` attribute to implement the
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``appendpath`` policy for example).
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.. FIXME: Replace the appendpath example if/when it's deprecated ;)
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An option can take different values depending on the context it is used. Such
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a context can involve configuration files, options from the command line,
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default values in bzrlib and then some.
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Such a context is implemented by creating a list of ``Section`` stacked upon
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each other. A ``Stack`` can then be asked for an option value and returns the
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first definition found.
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This provides a great flexibility to decide priorities between sections when
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the stack is defined without to worry about them in the code itself.
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A stack also defines a mutable section (which can be None) to handle
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Many sections (or even stores) are aimed at providing default values for an
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option but these sections shouldn't be modified lightly as modifying an option
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used for different contexts will indeed be seen by all these contexts.
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Default values in configuration files are defined by users. Developers
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shouldn't have to modify them, as such, no mechanism nor heuristics are used
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to find which section (or sections) should be modified.
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A ``Stack`` defines a mutable section when there is no ambiguity. If there
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is one, then the *user* should be able to decide and in this case a new
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``Stack`` can be created cheaply.
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Different stacks can be created for different purposes, the existing
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``GlobalStack``, ``LocationStack`` and ``BranchStack`` can be used as basis
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or examples. These classes are the only ones that should be used in code,
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``Stores`` can be used to build them but shouldn't be used otherwise, ditto
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for sections. Again, the associated tests could and should be used against the
added
removed
doc/developers/configuration.txt
