doctest comments not getting trimmed since Sphinx 1.8.0

[ngoldbaum]

Doctest comments are showing up in the output of my documentation with recent builds of sphinx. If I build the same project with sphinx 1.7.9, the doctest comments do not show up.

To Reproduce
Steps to reproduce the behavior:

$ git clone https://github.com/yt-project/unyt
$ cd unyt/docs
$ pip install numpy sympy
$ cd docs
$ make html SPHINXOPTS="-D language=de"
$ # open _build/html/index/usage and see search for "doctest", if that shows up anywhere it's doing the wrong thing

You can see this for yourself showing up on ReadTheDocs on this page: https://unyt.readthedocs.io/en/stable/usage.html

Expected behavior
Doctest directives shouldn't show up in the doc build output

Your project
github.com/yt-project/unyt

Screenshots
You can see this on the readthedocs build for unyt, here's a screenshot of how it looks there:

Here's the same snippet built with Sphinx 1.7.9, the last version where this renders correctly:

Environment info

• OS: Ubuntu 18.04
• Python version: 3.7.3
• Sphinx version: 2.1.2
• Sphinx extensions:

extensions = [
    "sphinx.ext.autodoc",
    "sphinx.ext.viewcode",
    "sphinx.ext.doctest",
    "sphinx.ext.napoleon",
    "sphinx.ext.mathjax",
    "show_all_units",
]

(show_all_units is a custom extension that should be unrelated to this)