[AIRFLOW-815] Add prev/next execution dates to template variables

This patch adds the previous/next execution dates
to the default variables available in a template.

Closes apache#2033 from danielvdende/add-execution-dates

airflow/models.py

@@ -1474,6 +1474,9 @@ def get_template_context(self, session=None):
         yesterday_ds = (self.execution_date - timedelta(1)).isoformat()[:10]
         tomorrow_ds = (self.execution_date + timedelta(1)).isoformat()[:10]
 
+        prev_execution_date = task.dag.previous_schedule(self.execution_date)
+        next_execution_date = task.dag.following_schedule(self.execution_date)
+
         ds_nodash = ds.replace('-', '')
         ts_nodash = ts.replace('-', '').replace(':', '')
         yesterday_ds_nodash = yesterday_ds.replace('-', '')
@@ -1543,6 +1546,8 @@ def __repr__(self):
             'dag_run': dag_run,
             'run_id': run_id,
             'execution_date': self.execution_date,
+            'prev_execution_date': prev_execution_date,
+            'next_execution_date': next_execution_date,
             'latest_date': ds,
             'macros': macros,
             'params': params,

docs/code.rst

@@ -127,6 +127,8 @@ Variable                            Description
 ``{{ ts }}``                        same as ``execution_date.isoformat()``
 ``{{ ts_nodash }}``                 same as ``ts`` without ``-`` and ``:``
 ``{{ execution_date }}``            the execution_date, (datetime.datetime)
+``{{ prev_execution_date }}``       the previous execution date (if available) (datetime.datetime)
+``{{ next_execution_date }}``       the next execution date (datetime.datetime)
 ``{{ dag }}``                       the DAG object
 ``{{ task }}``                      the Task object
 ``{{ macros }}``                    a reference to the macros package, described below