Allow `part` to be a page loaded from a file

[So-Cool]

Description / Summary

Load part content from a file via the following ToC syntax

format: jb-book
root: index
parts:
  - file: part_1/index
    chapters:
      - file: part_1/chapter_1
      - file: part_1/chapter_2/index
        sections:
          - file: part_1/chapter_2/section_1
          - file: part_1/chapter_2/section_2

Value / benefit

• Allows to write individual preface for each part -- this page won't be numbered as opposed to individual chapters
• Makes the parts--chapters ToC syntax consistent with chapters--sections syntax

Implementation details

• The file key seems to be accepted for parts entries, but it has no effect on the ToC

Tasks to complete

No response

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[chrisjsewell]

Heya, unless I'm mistaken, this is not possible within the sphinx toctree framework:

A part equates to a single toctree in a file with a caption:

.. toctree::
   :caption: This is the part title

   chapter1
   chapter2

I don't see how you could make this fit with adding a part prefix, unless there were upstream changes to sphinx's toctree directive.
Not to say that I wouldn't welcome it, but I don't see how it can currently be achieved in a "trivial" manner

[So-Cool]

I thought it would be a matter of a simple tweak given that it worked in jupyter-book 0.10.1 (see source and book). Do you know what has changed with the migration to the new ToC syntax that broke this functionality?

[chrisjsewell]

Are you sure you shouldn't be using the jb-article format, which essentially start a level down, and would allow you to achieve this. This is probably how it was working previously

[So-Cool]

I've had 3 levels of nesting

- part: Part 1
  file: src/text/1_part_i/_part_i.md
  chapters:
  - file: src/text/1_part_i/1.0.md
    sections:
      - file: src/text/1_part_i/1.1.md

The jb-article documentation is quite sparse but I don't think it allows for complex nesting.

However, your comment put me on the right track to find a solution. By using the raw ToC syntax I can get the result that I want

root: index
entries:
  - file: part_1/index
    options:
      numbered: true
    entries:
      - file: part_1/chapter_1
      - file: part_1/chapter_2/index
        entries:
          - file: part_1/chapter_2/section_1

Maybe it's worth discussing the raw ToC syntax in the Jupyter Book documentation in case people are looking for non-standard ToC structures. What do you think?