Ajay9704 commented on issue #62457:
URL: https://github.com/apache/airflow/issues/62457#issuecomment-3958106348
Analysis of the start_date Inconsistency
I wanted to provide a clear summary of the inconsistency around start_date
in the template context. I’ve spent the past two days debugging this, including
using AI for some insights just to understand the flow better, but the core
issue seems to come from an earlier commit that updated only part of the system.
What Changed in Commit 518287ce7f
The commit “Runtime context shouldn't have start_date as a key (#46961)”
removed start_date from the runtime template context produced by
get_template_context(). However, the following places were not updated and
still reference it:
task-sdk/src/airflow/sdk/definitions/context.py
(This still defines start_date: DateTime in the Context TypedDict)
airflow-core/docs/templates-ref.rst
(This still documents {{ start_date }} as an available template field)
Because these areas did not get updated, they no longer match runtime
behavior.
Current State (Misaligned)
The current behavior looks like this:
Runtime context (get_template_context())
Does not include start_date
This is correct, as the commit intentionally removed it.
TypedDict (Context, located in
task-sdk/src/airflow/sdk/definitions/context.py)
Still lists start_date
This is incorrect, because the runtime no longer provides it.
Documentation (airflow-core/docs/templates-ref.rst)
Still documents {{ start_date }}
This is incorrect, because using it now raises an error.
User Impact
Right now, if a user follows the documentation and writes:
{{ start_date }}
they receive:
KeyError: 'start_date'
The only currently valid ways to access it are:
ti.start_date
task_instance.start_date
So documentation, type hints, and runtime behavior do not match.
Two Possible Fix Approaches
I see two logical directions to resolve this inconsistency. Both are
technically valid; the maintainers' intention will decide which is appropriate.
Option A: Remove start_date from TypedDict and Documentation
(Aligns with the intent of commit 518287ce7f)
This requires:
Removing the start_date entry from the Context TypedDict
File: task-sdk/src/airflow/sdk/definitions/context.py
Removing the reference to {{ start_date }} from the documentation
File: airflow-core/docs/templates-ref.rst
This would make type hints and documentation match the current runtime
behavior.
Option B: Add start_date Back to the Runtime Context
(If the project prefers keeping the old template behavior)
This would require updating the template context assembly in:
task-sdk/src/airflow/sdk/execution_time/task_runner.py
Specifically, restoring start_date inside the cached template context.
This would make runtime, documentation, and TypedDict consistent again, but
it would partially undo commit 518287ce7f.
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