Closes #9339

Problem

The ipython Sphinx directive executes code at the parse stage. When wrapped in a conditional directive like only with a false condition for the current builder, the code still runs:

.. only:: latex

   .. ipython::

      In [1]: dangerous_operation()

Building with html builder — the only:: latex condition is false, yet dangerous_operation() still executes. This is because Sphinx's only directive evaluates conditions at the post-transform stage, after all child directive run() methods have already been called.

Fix

Add _is_inside_excluded_only() to IPythonDirective. It walks up the parent node chain via self.state.parent, and if any ancestor is an only node whose expression evaluates to false for the current builder's tags, returns True. When true, run() returns [] early without executing code or calling setup/teardown.

Key insight: during nested_parse inside Only.run(), the only node is set as the parent in the docutils state machine, so self.state.parent is directly the only node — no fragile heuristics needed.

Changes

IPython/sphinxext/ipython_directive.py

• IPythonDirective._is_inside_excluded_only(): walks parent chain, evaluates only node expressions against env.app.tags
• IPythonDirective.run(): early return when inside an excluded only block

tests/test_ipython_directive.py (new)

• test_only_excluded_skips_execution: only:: latex under html builder → code not executed
• test_only_included_executes_normally: only:: html under html builder → code executed
• test_nested_only_skips_execution: nested only:: html > only:: latex → inner block skipped