doc: Makefile: add support for xelatex

This patch makes the "latexpdf" target compile the documentation with
xelatex instead of the default pdflatex engine.

The reason behind this is stated in [YOCTO #14357]: pdflatex does not
support compiling foreign characters, so we need to resort to another
engine, here xelatex.

It also increases the texmf config buf_size to 10000000 to avoid a
compilation error.

(From yocto-docs rev: 0a6944b9f90b4d3babbdec9dee18fb8195b0db06)

Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
(cherry picked from commit 93848842b3ad8aa6b9c9f46d60f2c2ad396c6971)
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

documentation/Makefile

@@ -61,9 +61,12 @@ epub: $(PNGs)
 	$(SOURCEDIR)/set_versions.py
 	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
 
+# Note: we need to pass buf_size here (which is also configurable from
+# texmf.cnf), to avoid following error:
+#   Unable to read an entire line---bufsize=200000. Please increase buf_size in texmf.cnf.
 latexpdf: $(PDFs)
 	$(SOURCEDIR)/set_versions.py
-	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+	buf_size=10000000 $(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
 
 all: html epub latexpdf
 

documentation/conf.py

@@ -158,9 +158,14 @@ html_last_updated_fmt = '%b %d, %Y'
 # Remove the trailing 'dot' in section numbers
 html_secnumber_suffix = " "
 
+# We need XeTeX to process special unicode character, sometimes the contributor
+# list from the release note contains those.
+# See https://docs.readthedocs.io/en/stable/guides/pdf-non-ascii-languages.html.
+latex_engine = 'xelatex'
+latex_use_xindy = False
 latex_elements = {
     'passoptionstopackages': '\\PassOptionsToPackage{bookmarksdepth=5}{hyperref}',
-    'preamble': '\\setcounter{tocdepth}{2}',
+    'preamble': '\\usepackage[UTF8]{ctex}\n\\setcounter{tocdepth}{2}',
 }
 
 # Make the EPUB builder prefer PNG to SVG because of issues rendering Inkscape SVG