[MERGE] workflows: added some documentation and some tests.

bzr revid: vmt@openerp.com-20130731151636-05lgd5i08rie6yqp

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diff --git a/doc/index.rst b/doc/index.rst
index a5af574d09e..4b988e747b4 100644
--- a/doc/index.rst
+++ b/doc/index.rst
@@ -14,6 +14,7 @@ OpenERP Server
    02_architecture
    03_module_dev
    04_security
+   workflows
    05_test_framework
    06_misc
    deployment-gunicorn
diff --git a/doc/workflows.rst b/doc/workflows.rst
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+++ b/doc/workflows.rst
@@ -0,0 +1,306 @@
+.. _workflows:
+
+Workflows
+=========
+
+In OpenERP, a workflow is a technical artefact to manage a set of "things to do"
+associated to the records of some data model. The workflow provides a higher-
+level way to organize the things to do on a record.
+
+More specifically, a workflow is a directed graph where the nodes are called
+"activities" and the arcs are called "transitions".
+
+- Activities define work that should be done within the OpenERP server, such as
+  changing the state of some records, or sending emails.
+
+- Transitions control how the workflow progresses from activity to activity.
+
+In the definition of a workflow, one can attach conditions, signals, and
+triggers to transitions, so that the behavior of the workflow depends on user
+actions (such as clicking on a button), changes to records, or arbitrary Python
+code.
+
+Basics
+------
+
+Defining a workflow with data files is straightforward: a record "workflow" is
+given together with records for the activities and the transitions. For
+instance, here is a simple sequence of two activities defined in XML::
+
+    <record id="test_workflow" model="workflow">
+        <field name="name">test.workflow</field>
+        <field name="osv">test.workflow.model</field>
+        <field name="on_create">True</field>
+    </record>
+
+    <record id="activity_a" model="workflow.activity">
+        <field name="wkf_id" ref="test_workflow"/>
+        <field name="flow_start">True</field>
+        <field name="name">a</field>
+        <field name="kind">function</field>
+        <field name="action">print_a()</field>
+    </record>
+    <record id="activity_b" model="workflow.activity">
+        <field name="wkf_id" ref="test_workflow"/>
+        <field name="flow_stop">True</field>
+        <field name="name">b</field>
+        <field name="kind">function</field>
+        <field name="action">print_b()</field>
+    </record>
+
+    <record id="trans_a_b" model="workflow.transition">
+        <field name="act_from" ref="activity_a"/>
+        <field name="act_to" ref="activity_b"/>
+    </record>
+
+A worfklow is always defined with respect to a particular model (the model is
+given by the attribute ``osv`` on the model ``workflow``). Methods specified in
+the activities or transitions will be called on that model.
+
+In the example code above, a workflow called "test_workflow" is created. It is
+made up of two activies, named "a" and "b", and one transition, going from "a"
+to "b".
+
+The first activity has its attribute ``flow_start`` set to ``True`` so that
+OpenERP knows where to start the workflow traversal after it is instanciated.
+Because ``on_create`` is set to True on the workflow record, the workflow is
+instanciated for each newly created record. (Otherwise, the workflow should be
+instanciated by other means, such as from some module Python code.)
+
+When the workflow is instanciated, it begins with activity "a". That activity
+is of kind ``function``, which means that the action ``print_a()`` is a method
+call on the model ``test.workflow`` (the usual ``cr, uid, ids, context``
+arguments are passed for you).
+
+The transition between "a" and "b" does not specify any condition. This means
+that the workflow instance immediately goes from "a" to "b" after "a" has been
+processed, and thus also processes activity "b".
+
+Transitions
+-----------
+
+Transitions provide the control structures to orchestrate a workflow. When an
+activity is completed, the workflow engine tries to get across transitions
+departing from the completed activity, towards the next activities. In their
+simplest form (as in the example above), they link activities sequentially:
+activities are processed as soon as the activities preceding them are completed.
+
+Instead of running all activities in one fell swoop, it is also possible to wait
+on transitions, going through them only when some criteria are met. The criteria
+are the conditions, the signals, and the triggers. They are detailed in the
+following sections.
+
+Conditions
+''''''''''
+
+When an activity has been completed, its outgoing transitions are inspected to
+determine whether it is possible for the workflow instance to proceed through
+them and reach the next activities. When only a condition is defined (i.e., no
+signal or trigger is defined), the condition is evaluated by OpenERP, and if it
+evaluates to ``True``, the worklfow instance progresses through the transition.
+If the condition is not met, it will be reevaluated every time the associated
+record is modified, or by an explicit method call to do it.
+
+By default, the attribute ``condition`` (i.e., the expression to be evaluated)
+is just "True", which trivially evaluates to ``True``. Note that the condition
+may be several lines long; in that case, the value of the last one determines
+whether the transition can be taken.
+
+In the condition evaluation environment, several symbols are conveniently
+defined (in addition to the OpenERP ``safe_eval`` environment):
+
+- all the model column names, and
+- all the browse record's attributes.
+
+Signals
+'''''''
+
+In addition to a condition, a transition can specify a signal name. When such
+a signal name is present, the transition is not taken directly, even if the
+condition evaluates to ``True``. Instead the transition blocks, waiting to be
+woken up.
+
+In order to wake up a transition with a defined signal name, the signal must be
+sent to the workflow instance. A common way to send a signal is to use a button
+in the user interface, using the element ``<button/>`` with the signal name as
+the attribute ``name`` of the button. Once the button is clicked, the signal is
+sent to the workflow instance of the current record.
+
+.. note:: The condition is still evaluated when the signal is sent to the
+    workflow instance.
+
+Triggers
+''''''''
+
+With conditions that evaluate to ``False``, transitions are not taken (and thus
+the activity it leads to is not processed immediately). Still, the workflow
+instance can get new chances to progress across that transition by providing
+so-called triggers. The idea is that when the condition is not satisfied,
+triggers are recorded in database. Later, it is possible to wake up
+specifically the workflow instances that installed those triggers, offering
+them to reevaluate their transition conditions. This mechanism makes it cheaper
+to wake up workflow instances by targetting just a few of them (those that have
+installed the triggers) instead of all of them.
+
+Triggers are recorded in database as record IDs (together with the model name)
+and refer to the workflow instance waiting for those records. The transition
+definition provides a model name (attribute ``trigger_model``) and a Python
+expression (attribute ``trigger_expression``) that evaluates to a list of record
+IDs in the given model. Any of those records can wake up the workflow instance
+they are associated with.
+
+.. note:: Note that triggers are not re-installed whenever the transition is
+    re-tried.
+
+Splitting and joining transitions
+'''''''''''''''''''''''''''''''''
+
+When multiple transitions leave the same activity, or lead to the same activity,
+OpenERP provides some control over which transitions are actually taken, or how
+the reached activity will be processed. The attributes ``split_mode`` and
+``join_mode`` on the activity are used for such control. The possible values of
+those attributes are explained below.
+
+Activities
+----------
+
+While the transitions can be seen as the control structures of the workflows,
+activities are the places where everything happens, from changing record states
+to sending email.
+
+Different kinds of activities exist: ``Dummy``, ``Function``, ``Subflow``, and
+``Stop all``, each doing different things when the activity is processed. In
+addition to their kind, activies have other properties, detailed in the next
+sections.
+
+Flow start and flow stop
+''''''''''''''''''''''''
+
+The attribute ``flow_start`` is a boolean value specifying whether the activity
+is processed when the workflow is instanciated. Multiple activities can have
+their attribute ``flow_start`` set to ``True``. When instanciating a workflow
+for a record, OpenERP simply processes all of them, and evaluate all their
+outgoing transitions afterwards.
+
+The attribute ``flow_stop`` is a boolean value specifying whether the activity
+stops the workflow instance. A workflow instance is considered completed when
+all its activities with the attribute ``flow_stop`` set to ``True`` are
+completed.
+
+It is important for OpenERP to know when a workflow instance is completed. A
+workflow can have an activity that is actually another workflow (called a
+subflow); that activity is completed when the subflow is completed.
+
+Subflow
+'''''''
+
+An activity can embed a complete workflow, called a subflow (the embedding
+workflow is called the parent workflow). The workflow to instanciate is
+specified by attribute ``subflow_id``.
+
+.. note:: In the GUI, that attribute can not be set unless the kind of the
+    activity is ``Subflow``.
+
+The activity is considered completed (and its outgoing transitions ready to be
+evaluated) when the subflow is completed (see attribute ``flow_stop`` above).
+
+Sending a signal from a subflow
+'''''''''''''''''''''''''''''''
+
+When a workflow is embedded in an activity (as a subflow) of a workflow, the
+sublow can send a signal from its own activities to the parent workflow by
+giving a signal name in the attribute ``signal_send``. OpenERP processes those
+activities by sending the value of ``signal_send`` prefixed by "subflow."  to
+the parent workflow instance.
+
+In other words, it is possible to react and get transitions in the parent
+workflow as activities are executed in the sublow.
+
+Server actions
+''''''''''''''
+
+An activity can run a "Server Action" by specifying its ID in the attribute
+``action_id``.
+
+Python action
+'''''''''''''
+
+An activity can execute some Python code, given by the attribute ``action``.
+The evaluation environment is the same as the one explained in the section
+`Conditions`_.
+
+Split mode
+''''''''''
+
+After an activity has been processed, its outgoing transitions are evaluated.
+Normally, if a transition can be taken, OpenERP traverses it and proceed to the
+activity the transition leads to.
+
+Actually, when more than a single transition is leaving an activity, OpenERP may
+proceed or not, depending on the other transitions. That is, the conditions on
+the transitions can be combined together, and the combined result instructs
+OpenERP to traverse zero, one, or all the transitions. The way they are combined
+is controlled by the attribute ``split_mode``.
+
+There are three possible split modes: ``XOR``, ``OR`` and ``AND``.
+
+``XOR``
+    When the transitions are combined with a ``XOR`` split mode, as soon as a
+    transition has a satisfied condition, the transition is traversed and the
+    others are skipped.
+
+``OR``
+    With the ``OR`` mode, all the transitions with a satisfied condition are
+    traversed. The remaining transitions will not be evaluated later.
+
+``AND``
+    With the ``AND`` mode, OpenERP will wait for all outgoing transition
+    conditions to be satisfied, then traverse all of them at once.
+
+Join mode
+'''''''''
+
+Just like outgoing transition conditions can be combined together to decide
+whether they can be traversed or not, incoming transitions can be combined
+together to decide if and when an activity may be processed. The attribute
+``join_mode`` controls that behavior.
+
+There are two possible join modes: ``XOR`` and ``AND``.
+
+``XOR``
+    With the ``XOR`` mode, an incoming transition with a satisfied condition is
+    traversed immediately, and enables the processing of the activity.
+
+``AND``
+    With the ``AND`` mode, OpenERP will wait until all incoming transitions have
+    been traversed before enabling the processing of the activity.
+
+Kinds
+'''''
+
+Activities can be of different kinds: ``dummy``, ``function``, ``subflow``, or
+``stopall``. The kind defines what type of work an activity can do.
+
+Dummy
+    The ``dummy`` kind is for activities that do nothing, or for activities that
+    only call a server action. Activities that do nothing can be used as hubs to
+    gather/dispatch transitions.
+
+Function
+    The ``function`` kind is for activities that only need to run some Python
+    code, and possibly a server action.
+
+Stop all
+    The ``stopall`` kind is for activities that will completely stop the
+    workflow instance and mark it as completed. In addition they can also run
+    some Python code.
+
+Subflow
+    When the kind of the activity is ``subflow``, the activity embeds another
+    workflow instance. When the subflow is completed, the activity is also
+    considered completed.
+
+    By default, the subflow is instanciated for the same record as the parent
+    workflow. It is possible to change that behavior by providing Python code
+    that returns a record ID (of the same data model as the subflow). The
+    embedded subflow instance is then the one of the given record.