RST directives inside Napoleon-processed blocks are not handled correctly by gettext

[scarletcafe]

Describe the bug

Consider this function:

def documented_function(small: bool = False):
    """
    Use this when you want to look at a picture of a duck.

    Parameters
    -----------
    small: :class:`bool`
        Whether the duck should be small or not.

        .. warning::
            This duck is very small.

    Returns
    --------
    str
        A nice `picture of a duck`__.

        .. _picture_of_a_duck: https://upload.wikimedia.org/wikipedia/commons/5/51/Mandarin.duck.arp.jpg
        __ picture_of_a_duck_

    """
    ...

When directives .. warning:: and .. _picture_of_a_duck: are outside of the Parameters/Returns blocks, they get handled by gettext as normal (as in, the directives themselves are not included, only the respective text is).

However, running make gettext results in this in the .pot files:

#: ../../../foobar/__init__.py:docstring of foobar.documented_function:3
msgid "Whether the duck should be small or not.  .. warning::     This duck is very small."
msgstr ""

#: ../../../foobar/__init__.py:docstring of foobar.documented_function:3
msgid "Whether the duck should be small or not."
msgstr ""

#: ../../../foobar/__init__.py:docstring of foobar.documented_function:6
msgid "This duck is very small."
msgstr ""

#: ../../../foobar/__init__.py:docstring of foobar.documented_function:9
msgid "A nice `picture of a duck`__.  .. _picture_of_a_duck: https://upload.wikimedia.org/wikipedia/commons/5/51/Mandarin.duck.arp.jpg __ picture_of_a_duck_"
msgstr ""

#: ../../../foobar/__init__.py:docstring of foobar.documented_function:9
msgid "A nice `picture of a duck`__."
msgstr ""

Despite the correct handling being included afterwards, any point at which this occurs includes a wrongly-"folded" version at the beginning, and this is the version Sphinx ends up actually using.

This version is not translatable, as changing into the correct formatting causes Sphinx to error from formatting/indentation complaints, and leaving them as is results in them being presented "as is" in the document (unparsed plaintext).

How to Reproduce

$ git clone https://github.com/Gorialis/sphinx-napoleon-gettext-bug
$ cd sphinx-napoleon-gettext-bug
$ pip install -r requirements.txt
$ cd docs
$ PYTHONPATH=$(cd .. && pwd) make gettext

Expected behavior

Only the individual parts without the directives should be included, so they do not take priority over the 'correct' versions that follow such that the docstrings can be correctly translated.

Your project

https://github.com/Gorialis/sphinx-napoleon-gettext-bug

Screenshots

It is worth noting that despite it being handled by gettext incorrectly, this directive-in-parameter format IS accepted by Sphinx's html builder itself. It just breaks the translated versions.

OS

Windows 10 Pro 21H2 19044.1586 / Arch Linux on kernel 5.16.2

Python version

3.10.2

Sphinx version

4.5.0

Sphinx extensions

sphinx.ext.autodoc, sphinx.ext.napoleon

Extra tools

No response

Additional context

No response

[shiftinv]

Looked into this further, since I've seen it happen as well - it's not specific to napoleon, it occurs with the base :param: and :returns: fields as well (without the intermediate napoleon step).

With something like a .. versionadded:: 1.0 in the parameter description, it gets parsed into a node like this:

<inline:
  <paragraph: "description here">
  <versionmodified: <paragraph: ...>>
>

Without it, it ends up as a simple <inline: <#text: "description here">>.
The method description looks similar, although with a desc_content instead of an inline node.

As far as I can tell, the issue comes down to the fact that both the inline node above and the contained paragraph are considered translatable, whereas in the method description case, the desc_content node isn't translatable, as intended.
The inline generated for the param (or any field list item, really) indiscriminately receives a translatable=True, which probably isn't correct?

sphinx/sphinx/util/docfields.py

Lines 332 to 333 in 318914f

	translatable_content = nodes.inline(field_body.rawsource,
	translatable=True)

I unfortunately don't know enough about sphinx internals to properly fix it myself, but perhaps this can aid someone more knowledgeable.