docs: html: load stylesheet via custom.css.source

Until now the meson built docs did not have a working reference to the css
stylesheet, it was copied in the make target. Instead of duplicating that for
meson, use the docbook-xsl parameter custom.css.source to reference it. An
additional benefit of that approach is that the stylesheet is now included in
the single-file HTML documentation.

Reported-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Discussion: https://postgr.es/m/3fc3bb9b-f7f8-d442-35c1-ec82280c564a@enterprisedb.com

doc/src/sgml/Makefile

@@ -39,7 +39,7 @@ ifndef FOP
 FOP = $(missing) fop
 endif
 
-XMLINCLUDE = --path .
+XMLINCLUDE = --path . --path $(srcdir)
 
 ifdef XMLLINT
 XMLLINT := $(XMLLINT) --nonet
@@ -144,7 +144,6 @@ html: html-stamp
 
 html-stamp: stylesheet.xsl postgres-full.xml $(ALL_IMAGES)
 	$(XSLTPROC) $(XMLINCLUDE) $(XSLTPROCFLAGS) $(XSLTPROC_HTML_FLAGS) $(wordlist 1,2,$^)
-	cp $(srcdir)/stylesheet.css html/
 	touch $@
 
 # single-page HTML

doc/src/sgml/meson.build

@@ -96,7 +96,7 @@ if xsltproc_bin.found()
   xsltproc_flags = [
     '--nonet',
     '--stringparam', 'pg.version', pg_version,
-    '--path', '@OUTDIR@',
+    '--path', '@OUTDIR@', '--path', '@CURRENT_SOURCE_DIR@',
   ]
 
   xsltproc = xmltools_wrapper + [

doc/src/sgml/stylesheet-html-common.xsl

@@ -18,6 +18,14 @@
 <xsl:param name="make.graphic.viewport" select="0"/>
 <xsl:param name="link.mailto.url">pgsql-docs@lists.postgresql.org</xsl:param>
 <xsl:param name="toc.max.depth">2</xsl:param>
+<xsl:param name="website.stylesheet" select="0"/>
+<xsl:param name="custom.css.source">
+  <xsl:if test="$website.stylesheet = 0">stylesheet.css.xml</xsl:if>
+</xsl:param>
+<xsl:param name="html.stylesheet">
+  <xsl:if test="not($website.stylesheet = 0)">https://www.postgresql.org/media/css/docs-complete.css</xsl:if>
+</xsl:param>
+
 
 <!--
   The below allows the stylesheets provided by the website to be applied fully

doc/src/sgml/stylesheet-html-nochunk.xsl

@@ -7,6 +7,9 @@
 <xsl:include href="stylesheet-html-common.xsl" />
 <xsl:include href="stylesheet-speedup-xhtml.xsl" />
 
+<!-- except when referencing the online stylesheet, embed stylesheet -->
+<xsl:param name="generate.css.header" select="$website.stylesheet = 0"/>
+
 <!-- embed SVG images into output file -->
 <xsl:template match="imagedata[@format='SVG']">
   <xsl:variable name="filename">

doc/src/sgml/stylesheet.css.xml

@@ -0,0 +1,8 @@
+<!--
+    wrapper around stylesheet.css.xml to allow it to be loaded via docbook-xsl's
+    generate.css.header parameter.
+-->
+<!DOCTYPE style [
+<!ENTITY css SYSTEM "stylesheet.css">
+]>
+<style>&css;</style>

doc/src/sgml/stylesheet.xsl

@@ -17,17 +17,6 @@
 <xsl:param name="chunk.quietly" select="1"></xsl:param>
 <xsl:param name="admon.style"></xsl:param>  <!-- handled by CSS stylesheet -->
 
-<xsl:param name="website.stylesheet" select="0"/>
-
-<xsl:param name="html.stylesheet">
-  <xsl:choose>
-    <xsl:when test="$website.stylesheet = 0">stylesheet.css</xsl:when>
-    <xsl:otherwise>
-      https://www.postgresql.org/media/css/docs-complete.css
-    </xsl:otherwise>
-  </xsl:choose>
-</xsl:param>
-
 
 <!-- copy images to the output directory, so the output is self contained -->
 <xsl:template match="imageobject">