docs: pdfdocs: Pull LaTeX preamble part out of conf.py

Quote from Jon's remark [1]:

    I do notice that Documentation/conf.py is getting large and
    unapproachable.  At some future point, it might be nice to pull
    all of the latex stuff out into a separate file where it won't
    scare people who stumble into it by accident.

Pull LaTeX preamble settings added since commit 3b4c963243b1 ("docs:
conf.py: adjust the LaTeX document output") out into
sphinx/kerneldoc-preamble.sty.

It will be copied to the build directory by the added
"latex_additional_files" setting in conf.py.

As a bonus, LaTeX/TeX code can be maintained without escaping backslashes.

To compensate the loss of change history in sphinx/kerneldoc-preamble.sty,
here is a list of changes made in conf.py:

  - f7ebe6b76940 ("docs: Activate exCJK only in CJK chapters")
  - 0afd4df0d16a ("docs: pdfdocs: Prevent column squeezing by tabulary")
  - 659653c9e546 ("docs: pdfdocs: Refactor config for CJK document")
  - e291ff6f5a03 ("docs: pdfdocs: Add CJK-language-specific font settings")
  - 7eb368cc319b ("docs: pdfdocs: Choose Serif font as CJK mainfont if possible")
  - 35382965bdd2 ("docs: pdfdocs: Preserve inter-phrase space in Korean translations")
  - 77abc2c230b1 ("docs: pdfdocs: One-half spacing for CJK translations")
  - 788d28a25799 ("docs: pdfdocs: Permit AutoFakeSlant for CJK fonts")
  - 29ac9822358f ("docs: pdfdocs: Teach xeCJK about character classes of quotation marks")
  - 7c5c18bdb656 ("docs: pdfdocs: Fix typo in CJK-language specific font settings")
  - aa872e0647dc ("docs: pdfdocs: Adjust \headheight for fancyhdr")
  - 8716ef413aa5 ("docs: pdfdocs: Tweak width params of TOC")
  - 66939df53948 ("docs: pdfdocs: Switch default CJK font to KR variants")
  - 7b686a2ea1e4 ("docs: pdfdocs: Enable CJKspace in TOC for Korean titles")
  - 5d9158e3c762 ("docs/translations: Skip CJK contents if suitable fonts not found")
  - b774cc46313b ("docs: pdfdocs: Move CJK monospace font setting to main conf.py")

[1]: https://lore.kernel.org/all/87zgmr66cn.fsf@meer.lwn.net/

Suggested-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Link: https://lore.kernel.org/r/aaa9dca1-27c0-c414-77f3-c5587db0cc5b@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 184 insertions, 0 deletions

diff --git a/Documentation/sphinx/kerneldoc-preamble.sty b/Documentation/sphinx/kerneldoc-preamble.sty
new file mode 100644
index 000000000000..4e56ccea1dbd
--- /dev/null
+++ b/Documentation/sphinx/kerneldoc-preamble.sty
@@ -0,0 +1,184 @@
+% -*- coding: utf-8 -*-
+% SPDX-License-Identifier: GPL-2.0
+%
+% LaTeX preamble for "make latexdocs" or "make pdfdocs" including:
+%   - TOC width settings
+%   - Setting of tabulary (\tymin)
+%   - Headheight setting for fancyhdr
+%   - Fontfamily settings for CJK (Chinese, Japanese, and Korean) translations
+%
+% Note on the suffix of .sty:
+%   This is not implemented as a LaTeX style file, but as a file containing
+%   plain LaTeX code to be included into preamble.
+%   ".sty" is chosen because ".tex" would cause the build scripts to confuse
+%   this file with a LaTeX main file.
+%
+% Copyright (C) 2022  Akira Yokosawa
+
+% Custom width parameters for TOC --- Redefine low-level commands
+% defined in report.cls
+\makeatletter
+%% Redefine \@pnumwidth (page number width)
+\renewcommand*\@pnumwidth{2.7em}
+%% Redefine \l@chapter (chapter list entry)
+\renewcommand*\l@chapter[2]{%
+  \ifnum \c@tocdepth >\m@ne
+    \addpenalty{-\@highpenalty}%
+    \vskip 1.0em \@plus\p@
+    \setlength\@tempdima{1.8em}%
+    \begingroup
+      \parindent \z@ \rightskip \@pnumwidth
+      \parfillskip -\@pnumwidth
+      \leavevmode \bfseries
+      \advance\leftskip\@tempdima
+      \hskip -\leftskip
+      #1\nobreak\hfil
+      \nobreak\hb@xt@\@pnumwidth{\hss #2%
+                                 \kern-\p@\kern\p@}\par
+      \penalty\@highpenalty
+    \endgroup
+  \fi}
+%% Redefine \l@section and \l@subsection
+\renewcommand*\l@section{\@dottedtocline{1}{1.8em}{3.2em}}
+\renewcommand*\l@subsection{\@dottedtocline{2}{5em}{4.3em}}
+\makeatother
+%% Sphinx < 1.8 doesn't have \sphinxtableofcontentshook
+\providecommand{\sphinxtableofcontentshook}{}
+%% Undefine it for compatibility with Sphinx 1.7.9
+\renewcommand{\sphinxtableofcontentshook}{} % Empty the hook
+% Prevent column squeezing of tabulary.
+\setlength{\tymin}{20em}
+
+% Adjust \headheight for fancyhdr
+\addtolength{\headheight}{1.6pt}
+\addtolength{\topmargin}{-1.6pt}
+
+% Translations have Asian (CJK) characters which are only displayed if
+% xeCJK is used
+\IfFontExistsTF{Noto Sans CJK SC}{
+    % This is needed for translations
+    \usepackage{xeCJK}
+    \IfFontExistsTF{Noto Serif CJK KR}{
+	\setCJKmainfont{Noto Serif CJK KR}[AutoFakeSlant]
+    }{
+	\setCJKmainfont{Noto Sans CJK KR}[AutoFakeSlant]
+    }
+    \setCJKsansfont{Noto Sans CJK KR}[AutoFakeSlant]
+    \setCJKmonofont{Noto Sans Mono CJK KR}[AutoFakeSlant]
+    \xeCJKDeclareCharClass{HalfLeft}{`“,`‘}
+    \xeCJKDeclareCharClass{HalfRight}{`”,`’}
+    % CJK Language-specific font choices
+    \IfFontExistsTF{Noto Serif CJK SC}{
+	\newCJKfontfamily[SCmain]\scmain{Noto Serif CJK SC}[AutoFakeSlant]
+	\newCJKfontfamily[SCserif]\scserif{Noto Serif CJK SC}[AutoFakeSlant]
+    }{
+	\newCJKfontfamily[SCmain]\scmain{Noto Sans CJK SC}[AutoFakeSlant]
+	\newCJKfontfamily[SCserif]\scserif{Noto Sans CJK SC}[AutoFakeSlant]
+    }
+    \newCJKfontfamily[SCsans]\scsans{Noto Sans CJK SC}[AutoFakeSlant]
+    \newCJKfontfamily[SCmono]\scmono{Noto Sans Mono CJK SC}[AutoFakeSlant]
+    \IfFontExistsTF{Noto Serif CJK TC}{
+	\newCJKfontfamily[TCmain]\tcmain{Noto Serif CJK TC}[AutoFakeSlant]
+	\newCJKfontfamily[TCserif]\tcserif{Noto Serif CJK TC}[AutoFakeSlant]
+    }{
+	\newCJKfontfamily[TCmain]\tcmain{Noto Sans CJK TC}[AutoFakeSlant]
+	\newCJKfontfamily[TCserif]\tcserif{Noto Sans CJK TC}[AutoFakeSlant]
+    }
+    \newCJKfontfamily[TCsans]\tcsans{Noto Sans CJK TC}[AutoFakeSlant]
+    \newCJKfontfamily[TCmono]\tcmono{Noto Sans Mono CJK TC}[AutoFakeSlant]
+    \IfFontExistsTF{Noto Serif CJK KR}{
+	\newCJKfontfamily[KRmain]\krmain{Noto Serif CJK KR}[AutoFakeSlant]
+	\newCJKfontfamily[KRserif]\krserif{Noto Serif CJK KR}[AutoFakeSlant]
+    }{
+	\newCJKfontfamily[KRmain]\krmain{Noto Sans CJK KR}[AutoFakeSlant]
+	\newCJKfontfamily[KRserif]\krserif{Noto Sans CJK KR}[AutoFakeSlant]
+    }
+    \newCJKfontfamily[KRsans]\krsans{Noto Sans CJK KR}[AutoFakeSlant]
+    \newCJKfontfamily[KRmono]\krmono{Noto Sans Mono CJK KR}[AutoFakeSlant]
+    \IfFontExistsTF{Noto Serif CJK JP}{
+	\newCJKfontfamily[JPmain]\jpmain{Noto Serif CJK JP}[AutoFakeSlant]
+	\newCJKfontfamily[JPserif]\jpserif{Noto Serif CJK JP}[AutoFakeSlant]
+    }{
+	\newCJKfontfamily[JPmain]\jpmain{Noto Sans CJK JP}[AutoFakeSlant]
+	\newCJKfontfamily[JPserif]\jpserif{Noto Sans CJK JP}[AutoFakeSlant]
+    }
+    \newCJKfontfamily[JPsans]\jpsans{Noto Sans CJK JP}[AutoFakeSlant]
+    \newCJKfontfamily[JPmono]\jpmono{Noto Sans Mono CJK JP}[AutoFakeSlant]
+    % Dummy commands for Sphinx < 2.3 (no 'extrapackages' support)
+    \providecommand{\onehalfspacing}{}
+    \providecommand{\singlespacing}{}
+    % Define custom macros to on/off CJK
+    \newcommand{\kerneldocCJKon}{\makexeCJKactive\onehalfspacing}
+    \newcommand{\kerneldocCJKoff}{\makexeCJKinactive\singlespacing}
+    \newcommand{\kerneldocBeginSC}{%
+	\begingroup%
+	\scmain%
+	\xeCJKDeclareCharClass{FullLeft}{`“,`‘}%
+	\xeCJKDeclareCharClass{FullRight}{`”,`’}%
+	\renewcommand{\CJKrmdefault}{SCserif}%
+	\renewcommand{\CJKsfdefault}{SCsans}%
+	\renewcommand{\CJKttdefault}{SCmono}%
+	\xeCJKsetup{CJKspace = false}%
+	% For CJK ascii-art alignment
+	\setmonofont{Noto Sans Mono CJK SC}[AutoFakeSlant]%
+    }
+    \newcommand{\kerneldocEndSC}{\endgroup}
+    \newcommand{\kerneldocBeginTC}{%
+	\begingroup%
+	\tcmain%
+	\xeCJKDeclareCharClass{FullLeft}{`“,`‘}%
+	\xeCJKDeclareCharClass{FullRight}{`”,`’}%
+	\renewcommand{\CJKrmdefault}{TCserif}%
+	\renewcommand{\CJKsfdefault}{TCsans}%
+	\renewcommand{\CJKttdefault}{TCmono}%
+	\xeCJKsetup{CJKspace = false}%
+	% For CJK ascii-art alignment
+	\setmonofont{Noto Sans Mono CJK TC}[AutoFakeSlant]%
+    }
+    \newcommand{\kerneldocEndTC}{\endgroup}
+    \newcommand{\kerneldocBeginKR}{%
+	\begingroup%
+	\krmain%
+	\renewcommand{\CJKrmdefault}{KRserif}%
+	\renewcommand{\CJKsfdefault}{KRsans}%
+	\renewcommand{\CJKttdefault}{KRmono}%
+	% \xeCJKsetup{CJKspace = true} % true by default
+	% For CJK ascii-art alignment (still misaligned for Hangul)
+	\setmonofont{Noto Sans Mono CJK KR}[AutoFakeSlant]%
+    }
+    \newcommand{\kerneldocEndKR}{\endgroup}
+    \newcommand{\kerneldocBeginJP}{%
+	\begingroup%
+	\jpmain%
+	\renewcommand{\CJKrmdefault}{JPserif}%
+	\renewcommand{\CJKsfdefault}{JPsans}%
+	\renewcommand{\CJKttdefault}{JPmono}%
+	\xeCJKsetup{CJKspace = false}%
+	% For CJK ascii-art alignment
+	\setmonofont{Noto Sans Mono CJK JP}[AutoFakeSlant]%
+    }
+    \newcommand{\kerneldocEndJP}{\endgroup}
+    % Single spacing in literal blocks
+    \fvset{baselinestretch=1}
+    % To customize \sphinxtableofcontents
+    \usepackage{etoolbox}
+    % Inactivate CJK after tableofcontents
+    \apptocmd{\sphinxtableofcontents}{\kerneldocCJKoff}{}{}
+    \xeCJKsetup{CJKspace = true} % For inter-phrase space of Korean TOC
+}{ % No CJK font found
+    % Custom macros to on/off CJK (Dummy)
+    \newcommand{\kerneldocCJKon}{}
+    \newcommand{\kerneldocCJKoff}{}
+    \newcommand{\kerneldocBeginSC}[1]{%
+	\begin{sphinxadmonition}{note}{Note:}
+	    ``Noto Sans CJK'' fonts are not found while building this PDF\@.
+	    Translations of zh\_CN, zh\_TW, ko\_KR, and ja\_JP are skipped.
+	\end{sphinxadmonition}}
+    \newcommand{\kerneldocEndSC}{}
+    \newcommand{\kerneldocBeginTC}[1]{}
+    \newcommand{\kerneldocEndTC}{}
+    \newcommand{\kerneldocBeginKR}[1]{}
+    \newcommand{\kerneldocEndKR}{}
+    \newcommand{\kerneldocBeginJP}[1]{}
+    \newcommand{\kerneldocEndJP}{}
+}