LaTeX: problems (frame, color) when long code line wraps over a page limit in some circumstances

[jfbu]

Describe the bug

Unexpected loss of frame on page 1 and color on page 2

How to Reproduce

.. raw:: latex

   \vspace*{18cm}

1. A list

   #) one

   #) two

   #) .. code-block:: python

         astr = "a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line"

Expected behavior

No response

Your project

N/A

Screenshots

OS

Mac

Python version

3.10.4

Sphinx version

5.x (v5.1.0+/12e86ff0e)

Sphinx extensions

No response

Extra tools

No response

Additional context

Relates #8686.

The #10577 works generally, but here something strange happens with a code-block as item in a numbered list.

edit:

• the issue is actually not at all related to lists, it happens with code-blocks at top level
• it has to do with syntax highlighting, the effect disappears with "none" as language.

Bug clearly related to the long code line being almost entirely an argument to a \PYG macro. Some problems with "groups" in TeX modifying scopes of certain things, presumably.

edit:

This has to do with Pygmentize mark-up assigning some color (not background color, which would create unbreakable box, here only foreground color) via \textcolor{<color>}{<long input>} to a long input which ends up split across pages (prior to #10577 the text would have spilled into bottom margin of first page). I have noticed that already LaTeX package framed has problems in such circumstances (the framing is partially contaminated by the text color, but text on second page has correct color). Inserting into a Sphinx LaTeX document

\begin{sphinxVerbatim}[commandchars=\\\{\}]
{{\color{blue} a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line}}
\end{sphinxVerbatim} 

at a location such that pagebreak occurs within it is enough to trigger the problem. With one level less of grouping {...}, the frame on first part reappears, but the color is still wrong on second page.

[jfbu]

This is a difficult problem which one can experience with pure LaTeX via this example

\documentclass[a4paper]{article}
\usepackage{framed}
\usepackage{color}
\definecolor{shadecolor}{rgb}{0.8,0.8,0.8}
\begin{document}
\vspace*{18cm}
\begin{shaded}
  \textcolor{blue}{a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line a very long line}\newline
  I am invisible
\end{shaded}
Hello
%\showoutput
\end{document}

On page 2, the long code line has lost its color. Moreover the line "I am invisible" is invisible because it acquires the color of the gray background.

The problem is due to a separation of a "color push" on page 1 and "color pop" on page 2, and the reason the background color is used is related to internals of core LaTeX \colorbox.

In the case of Sphinx, there are differences because it does both framing and background colors. I found also buggy situations with pure LaTeX+framed and its framed, not shaded, environment. Anyway, #10616 has partially fixed here, but not completely, see screenshots there.

I do not expect a fix anytime soon of the remainning problems so putting the milestone at 6.0.0.

edit: unexpectedly I could fix this. But this required a deep plunge into LaTeX core color interface, as some of its features are the root cause of this problem.