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+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+# Copyright (C) Akira Yokosawa, 2024
+#
+# For "make pdfdocs", reports of build errors of translations.pdf started
+# arriving early 2024 [1, 2]. It turned out that Fedora and openSUSE
+# tumbleweed have started deploying variable-font [3] format of "Noto CJK"
+# fonts [4, 5]. For PDF, a LaTeX package named xeCJK is used for CJK
+# (Chinese, Japanese, Korean) pages. xeCJK requires XeLaTeX/XeTeX, which
+# does not (and likely never will) understand variable fonts for historical
+# reasons.
+#
+# The build error happens even when both of variable- and non-variable-format
+# fonts are found on the build system. To make matters worse, Fedora enlists
+# variable "Noto CJK" fonts in the requirements of langpacks-ja, -ko, -zh_CN,
+# -zh_TW, etc. Hence developers who have interest in CJK pages are more
+# likely to encounter the build errors.
+#
+# This script is invoked from the error path of "make pdfdocs" and emits
+# suggestions if variable-font files of "Noto CJK" fonts are in the list of
+# fonts accessible from XeTeX.
+#
+# References:
+# [1]: https://lore.kernel.org/r/8734tqsrt7.fsf@meer.lwn.net/
+# [2]: https://lore.kernel.org/r/1708585803.600323099@f111.i.mail.ru/
+# [3]: https://en.wikipedia.org/wiki/Variable_font
+# [4]: https://fedoraproject.org/wiki/Changes/Noto_CJK_Variable_Fonts
+# [5]: https://build.opensuse.org/request/show/1157217
+#
+#===========================================================================
+# Workarounds for building translations.pdf
+#===========================================================================
+#
+# * Denylist "variable font" Noto CJK fonts.
+# - Create $HOME/deny-vf/fontconfig/fonts.conf from template below, with
+# tweaks if necessary. Remove leading "# ".
+# - Path of fontconfig/fonts.conf can be overridden by setting an env
+# variable FONTS_CONF_DENY_VF.
+#
+# * Template:
+# -----------------------------------------------------------------
+# <?xml version="1.0"?>
+# <!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd">
+# <fontconfig>
+# <!--
+# Ignore variable-font glob (not to break xetex)
+# -->
+# <selectfont>
+# <rejectfont>
+# <!--
+# for Fedora
+# -->
+# <glob>/usr/share/fonts/google-noto-*-cjk-vf-fonts</glob>
+# <!--
+# for openSUSE tumbleweed
+# -->
+# <glob>/usr/share/fonts/truetype/Noto*CJK*-VF.otf</glob>
+# </rejectfont>
+# </selectfont>
+# </fontconfig>
+# -----------------------------------------------------------------
+#
+# The denylisting is activated for "make pdfdocs".
+#
+# * For skipping CJK pages in PDF
+# - Uninstall texlive-xecjk.
+# Denylisting is not needed in this case.
+#
+# * For printing CJK pages in PDF
+# - Need non-variable "Noto CJK" fonts.
+# * Fedora
+# - google-noto-sans-cjk-fonts
+# - google-noto-serif-cjk-fonts
+# * openSUSE tumbleweed
+# - Non-variable "Noto CJK" fonts are not available as distro packages
+# as of April, 2024. Fetch a set of font files from upstream Noto
+# CJK Font released at:
+# https://github.com/notofonts/noto-cjk/tree/main/Sans#super-otc
+# and at:
+# https://github.com/notofonts/noto-cjk/tree/main/Serif#super-otc
+# , then uncompress and deploy them.
+# - Remember to update fontconfig cache by running fc-cache.
+#
+# !!! Caution !!!
+# Uninstalling "variable font" packages can be dangerous.
+# They might be depended upon by other packages important for your work.
+# Denylisting should be less invasive, as it is effective only while
+# XeLaTeX runs in "make pdfdocs".
+
+# Default per-user fontconfig path (overridden by env variable)
+: ${FONTS_CONF_DENY_VF:=$HOME/deny-vf}
+
+export XDG_CONFIG_HOME=${FONTS_CONF_DENY_VF}
+
+notocjkvffonts=`fc-list : file family variable | \
+ grep 'variable=True' | \
+ grep -E -e 'Noto (Sans|Sans Mono|Serif) CJK' | \
+ sed -e 's/^/ /' -e 's/: Noto S.*$//' | sort | uniq`
+
+if [ "x$notocjkvffonts" != "x" ] ; then
+ echo '============================================================================='
+ echo 'XeTeX is confused by "variable font" files listed below:'
+ echo "$notocjkvffonts"
+ echo
+ echo 'For CJK pages in PDF, they need to be hidden from XeTeX by denylisting.'
+ echo 'Or, CJK pages can be skipped by uninstalling texlive-xecjk.'
+ echo
+ echo 'For more info on denylisting, other options, and variable font, see header'
+ echo 'comments of scripts/check-variable-fonts.sh.'
+ echo '============================================================================='
+fi
+
+# As this script is invoked from Makefile's error path, always error exit
+# regardless of whether any variable font is discovered or not.
+exit 1