feat: Add optional static_url to BaseOperatorLink to skip XCom for constant links

[iRAFEEK]

Closes #55432

Problem

BaseOperatorLink.get_link() was an @abstractmethod, forcing every
subclass to implement it even when the link URL is a constant (e.g.,
a documentation link). This meant operators with static links still had
to push to XCom during execute() and read from the metadata database
on every task run, adding unnecessary overhead.

Solution

This PR introduces an optional static_url property on
BaseOperatorLink:

• static_url defaults to None (no behavior change for existing subclasses)
• get_link() is no longer @abstractmethod; its default implementation
  returns static_url if set, otherwise raises NotImplementedError
  with a helpful message guiding the developer to override one or the other
• Subclasses with a constant URL can now override static_url instead
  of get_link(), with zero XCom involvement

Backward Compatibility

Fully backward-compatible. All existing subclasses that implement
get_link() continue to work without any changes.

Example

class MyDocsLink(BaseOperatorLink):
    name = "Documentation"
    operators = [MyOperator]

    @property
    def static_url(self) -> str:
        return "https://myoperator.readthedocs.io"
    # No get_link() needed — no XCom push during execute()

Tests

Added task-sdk/tests/task_sdk/bases/test_operatorlink.py covering:

• static_url defaults to None
• Subclass using static_url returns correct URL from get_link()
• Subclass overriding get_link() directly still works (existing behavior)
• Subclass implementing neither raises NotImplementedError with a clear message
• name remains abstract

[boring-cyborg]

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[aaron-y-chen]

Hi, thanks for the PR! I wonder whether this would still write to XCom when static_url is set.

airflow/task-sdk/src/airflow/sdk/execution_time/task_runner.py

Lines 2261 to 2263 in 7217f84

	link, xcom_key = oe.get_link(operator=task, ti_key=ti), oe.xcom_key # type: ignore[arg-type]
	log.debug("Setting xcom for operator extra link", link=link, xcom_key=xcom_key)
	_xcom_push_to_db(ti, key=xcom_key, value=link)

It seems _xcom_push_to_db() is executed unconditionally after get_link(). Would you mind taking a look?

[zach-overflow]

It might be a good idea to add this informatio to the relevant site doc too.

[iRAFEEK]

@aaron-y-chen good catch, you're right. finalize() was pushing to XCom unconditionally after get_link(), so a static_url link was still persisted every run. Fixed in 8349e44: skip the push when the link is static. Safe because the render path (SerializedBaseOperator.get_extra_links) calls get_link() directly and never reads that XCom back. Dynamic links are unchanged; added a test covering both.

[iRAFEEK]

@zach-overflow good call, added a static_url note with an example to airflow-core/docs/howto/define-extra-link.rst in the same commit (8349e44). Thanks!

[iRAFEEK]

Thanks again for the reviews @aaron-y-chen @zach-overflow! I've pushed:

• the XCom fix (skip the _xcom_push_to_db() call in finalize() for static links, since the render path resolves them via get_link() directly) + a test, and
• the docs note for static_url, and
• a small lint follow-up (ruff PT012 + trailing newlines) after the newer ruff landed via main.

Everything's green locally (including ruff==0.16.0). Could a committer kick off / approve the CI workflows when you have a moment? Happy to address anything else. 🙏