Relax the linear flow symbol constraints

In order to make it possible to have a symbol
tree we need to relax and remove the constraints
that are being imposed by the linear constraints
and later move those constraint checks and validations
into the engines compilation stage.

Part of blueprint taskflow-improved-scoping

Change-Id: I6efdc821ff991e83572d89f56be5c678d007f9f8

1 files changed, 2 insertions, 31 deletions

diff --git a/taskflow/patterns/linear_flow.py b/taskflow/patterns/linear_flow.py
index 14799b8..7755923 100644
--- a/taskflow/patterns/linear_flow.py
+++ b/taskflow/patterns/linear_flow.py
@@ -14,7 +14,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from taskflow import exceptions
 from taskflow import flow
 
 
@@ -22,14 +21,11 @@ _LINK_METADATA = {'invariant': True}
 
 
 class Flow(flow.Flow):
-    """Linear Flow pattern.
+    """Linear flow pattern.
 
     A linear (potentially nested) flow of *tasks/flows* that can be
     applied in order as one unit and rolled back as one unit using
     the reverse order that the *tasks/flows* have been applied in.
-
-    NOTE(imelnikov): Tasks/flows contained in this linear flow must not
-    depend on outputs (provided names/values) of tasks/flows that follow it.
     """
 
     def __init__(self, name, retry=None):
@@ -38,32 +34,7 @@ class Flow(flow.Flow):
 
     def add(self, *items):
         """Adds a given task/tasks/flow/flows to this flow."""
-        if not items:
-            return self
-
-        # NOTE(imelnikov): we add item to the end of flow, so it should
-        # not provide anything previous items of the flow require.
-        requires = self.requires
-        provides = self.provides
-        for item in items:
-            requires |= item.requires
-            out_of_order = requires & item.provides
-            if out_of_order:
-                raise exceptions.DependencyFailure(
-                    "%(item)s provides %(oo)s that are required "
-                    "by previous item(s) of linear flow %(flow)s"
-                    % dict(item=item.name, flow=self.name,
-                           oo=sorted(out_of_order)))
-            same_provides = provides & item.provides
-            if same_provides:
-                raise exceptions.DependencyFailure(
-                    "%(item)s provides %(value)s but is already being"
-                    " provided by %(flow)s and duplicate producers"
-                    " are disallowed"
-                    % dict(item=item.name, flow=self.name,
-                           value=sorted(same_provides)))
-            provides |= item.provides
-
+        items = [i for i in items if i not in self._children]
         self._children.extend(items)
         return self