Refactor 4 different renderings of task description (#3743)

Prior to this PR, there were 4 variant ways to render a future (which is
usually but not always a Parsl task) as a text string:

1. describing failure of inner future in a join_app with 1 future to
join

- rendered task ID if the inner future has a task record attribute,
without checking it is a parsl.dataflow.taskrecord.TaskRecord or that
that attribute contains a task id entry.
 - otherwise render as None

2. describing failure of inner future in a join_app with a list of
futures to join

- is meant to do the same as case 1, but is buggy and always renders as
None (the wrong object is checked for having a task_record attribute)

3. describing failure of a dependency future

 - rendered task ID if there was a task_record, and the
   future is from the same DFK as is rendering the code
   (so that a task number from a different DFK is not
   rendered, in the corner case of a task from one DFK
   being used as a dependency for a task in another DFK)

 - otherwise, renders the repr of the future

4. describing which dependencies will be waited on when submitting a
task to the DFK

- rendered task ID if the future is an instance of AppFuture or
DataFuture
 - otherwise renders the repr of the future

This PR makes a single render method. It is a member of the DFK, because
rendering is done in the context of the DFK: two parsl task AppFutures
will be rendered differently if they are from this DFK or a different
DFK.

This PR implements render_future_description which tries to combine all
of the above:

 - if the future is an AppFuture, and is from the same
   DFK, render the task ID
 - otherwise render the repr of the future


# Changed Behaviour

human readable descriptions of dependencies/join inner futures will be
changed

# Fixes

Fixes # (issue)

## Type of change

Choose which options apply, and delete the ones which do not apply.

- Bug fix
- New feature
- Update to human readable text: Documentation/error messages/comments
- Code maintenance/cleanup

parsl/dataflow/dflow.py

@@ -484,24 +484,18 @@ def handle_join_update(self, task_record: TaskRecord, inner_app_future: Optional
 
             # now we know each joinable Future is done
             # so now look for any exceptions
-            exceptions_tids: List[Tuple[BaseException, Optional[str]]]
+            exceptions_tids: List[Tuple[BaseException, str]]
             exceptions_tids = []
             if isinstance(joinable, Future):
                 je = joinable.exception()
                 if je is not None:
-                    if hasattr(joinable, 'task_record'):
-                        tid = joinable.task_record['id']
-                    else:
-                        tid = None
+                    tid = self.render_future_description(joinable)
                     exceptions_tids = [(je, tid)]
             elif isinstance(joinable, list):
                 for future in joinable:
                     je = future.exception()
                     if je is not None:
-                        if hasattr(joinable, 'task_record'):
-                            tid = joinable.task_record['id']
-                        else:
-                            tid = None
+                        tid = self.render_future_description(future)
                         exceptions_tids.append((je, tid))
             else:
                 raise TypeError(f"Unknown joinable type {type(joinable)}")
@@ -918,13 +912,7 @@ def _unwrap_futures(self, args: Sequence[Any], kwargs: Dict[str, Any]) \
         dep_failures = []
 
         def append_failure(e: Exception, dep: Future) -> None:
-            # If this Future is associated with a task inside this DFK,
-            # then refer to the task ID.
-            # Otherwise make a repr of the Future object.
-            if hasattr(dep, 'task_record') and dep.task_record['dfk'] == self:
-                tid = "task " + repr(dep.task_record['id'])
-            else:
-                tid = repr(dep)
+            tid = self.render_future_description(dep)
             dep_failures.extend([(e, tid)])
 
         # Replace item in args
@@ -1076,10 +1064,7 @@ def submit(self,
 
         depend_descs = []
         for d in depends:
-            if isinstance(d, AppFuture) or isinstance(d, DataFuture):
-                depend_descs.append("task {}".format(d.tid))
-            else:
-                depend_descs.append(repr(d))
+            depend_descs.append(self.render_future_description(d))
 
         if depend_descs != []:
             waiting_message = "waiting on {}".format(", ".join(depend_descs))
@@ -1438,6 +1423,18 @@ def default_std_autopath(self, taskrecord, kw):
                 '' if label is None else '_{}'.format(label),
                 kw))
 
+    def render_future_description(self, dep: Future) -> str:
+        """Renders a description of the future in the context of the
+        current DFK.
+        """
+        if isinstance(dep, AppFuture) and dep.task_record['dfk'] == self:
+            tid = "task " + repr(dep.task_record['id'])
+        elif isinstance(dep, DataFuture):
+            tid = "DataFuture from task " + repr(dep.tid)
+        else:
+            tid = repr(dep)
+        return tid
+
 
 class DataFlowKernelLoader:
     """Manage which DataFlowKernel is active.

parsl/tests/test_python_apps/test_dep_standard_futures.py

@@ -43,3 +43,6 @@ def test_future_fail_dependency():
     # Future, plain_fut, somewhere in its str
 
     assert repr(plain_fut) in str(ex)
+    assert len(ex.dependent_exceptions_tids) == 1
+    assert isinstance(ex.dependent_exceptions_tids[0][0], ValueError)
+    assert ex.dependent_exceptions_tids[0][1].startswith("<Future ")

parsl/tests/test_python_apps/test_fail.py

@@ -27,17 +27,26 @@ def test_no_deps():
             pass
 
 
-@pytest.mark.parametrize("fail_probs", ((1, 0), (0, 1)))
-def test_fail_sequence(fail_probs):
-    """Test failure in a sequence of dependencies
+def test_fail_sequence_first():
+    t1 = random_fail(fail_prob=1)
+    t2 = random_fail(fail_prob=0, inputs=[t1])
+    t_final = random_fail(fail_prob=0, inputs=[t2])
 
-    App1 -> App2 ... -> AppN
-    """
+    with pytest.raises(DependencyError):
+        t_final.result()
 
-    t1_fail_prob, t2_fail_prob = fail_probs
-    t1 = random_fail(fail_prob=t1_fail_prob)
-    t2 = random_fail(fail_prob=t2_fail_prob, inputs=[t1])
+    assert len(t_final.exception().dependent_exceptions_tids) == 1
+    assert isinstance(t_final.exception().dependent_exceptions_tids[0][0], DependencyError)
+    assert t_final.exception().dependent_exceptions_tids[0][1].startswith("task ")
+
+
+def test_fail_sequence_middle():
+    t1 = random_fail(fail_prob=0)
+    t2 = random_fail(fail_prob=1, inputs=[t1])
     t_final = random_fail(fail_prob=0, inputs=[t2])
 
     with pytest.raises(DependencyError):
         t_final.result()
+
+    assert len(t_final.exception().dependent_exceptions_tids) == 1
+    assert isinstance(t_final.exception().dependent_exceptions_tids[0][0], ManufacturedTestFailure)

parsl/tests/test_python_apps/test_join.py

@@ -97,7 +97,10 @@ def test_error():
     f = outer_error()
     e = f.exception()
     assert isinstance(e, JoinError)
+
+    assert len(e.dependent_exceptions_tids) == 1
     assert isinstance(e.dependent_exceptions_tids[0][0], InnerError)
+    assert e.dependent_exceptions_tids[0][1].startswith("task ")
 
 
 def test_two_errors():
@@ -109,10 +112,12 @@ def test_two_errors():
     de0 = e.dependent_exceptions_tids[0][0]
     assert isinstance(de0, InnerError)
     assert de0.args[0] == "Error A"
+    assert e.dependent_exceptions_tids[0][1].startswith("task ")
 
     de1 = e.dependent_exceptions_tids[1][0]
     assert isinstance(de1, InnerError)
     assert de1.args[0] == "Error B"
+    assert e.dependent_exceptions_tids[1][1].startswith("task ")
 
 
 def test_one_error_one_result():
@@ -125,6 +130,7 @@ def test_one_error_one_result():
     de0 = e.dependent_exceptions_tids[0][0]
     assert isinstance(de0, InnerError)
     assert de0.args[0] == "Error A"
+    assert e.dependent_exceptions_tids[0][1].startswith("task ")
 
 
 @join_app