How to include an internal reference in a code block?

You can use the parsed-literal directive:

.. parsed-literal:: 

   |── :ref:`parent`
   |   |── :ref:`child`
   |       |── :ref:`grandchild`

This works, but there are warning messages saying "WARNING: Inline substitution_reference start-string without end-string."

The vertical bars are interpreted as parts of substitution references. The warnings go away with some escaping:

.. parsed-literal:: 

   \|── :ref:`parent`
   |   \|── :ref:`child`
   |       \|── :ref:`grandchild`

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