nixos: Split paras by \n\n in option descriptions

What annoyed me for a long time was the fact, that in order to break
into a new paragraph, you need to insert </para><para> in the
description attribute of an option.

Now we will automatically create <para/> elements for every block that
is separated by two consecutive newlines.

I first tried to do this within options-to-docbook.xsl, but it turns
out[1] that this isn't directly possible with XSLT 1.0, so I added
another XSLT file that postprocesses the option descriptions that are
now enclosed in <nixos:option-description/> by options-to-docbook.xsl.

The splitting itself is a bit more involved, because we can't simply
split on every \n\n because we'd also split text nodes of elements, for
example:

  <screen><![CDATA[

    one line

    another one

  ]]></screen>

This would create one <para/> element for "one line" and another for
"another line", which we obviously don't want because <screen/> is used
to display verbatim contents of what a user is seeing on the screen.

So what we do instead is splitting *only* the top-level text nodes
within the outermost <para/> and leave all elements as-is. If there are
more than one <para/> elements at the top-level, we simply don't process
it at all, because the description then already contains </para><para>.

https://www.mhonarc.org/archive/html/xsl-list/2012-09/msg00319.html

Signed-off-by: aszlig <aszlig@nix.build>
Cc: @edolstra, @domenkozar
This commit is contained in:
aszlig 2018-09-02 05:05:34 +02:00
parent 953b77f07b
commit f865d0feab
No known key found for this signature in database
GPG Key ID: 684089CE67EBB691
3 changed files with 125 additions and 5 deletions

View File

@ -90,7 +90,9 @@ let
fi
${buildPackages.libxslt.bin}/bin/xsltproc \
--stringparam revision '${revision}' \
-o $out ${./options-to-docbook.xsl} $optionsXML
-o intermediate.xml ${./options-to-docbook.xsl} $optionsXML
${buildPackages.libxslt.bin}/bin/xsltproc \
-o "$out" ${./postprocess-option-descriptions.xsl} intermediate.xml
'';
sources = lib.sourceFilesBySuffices ./. [".xml"];

View File

@ -4,6 +4,7 @@
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:str="http://exslt.org/strings"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:nixos="tag:nixos.org"
xmlns="http://docbook.org/ns/docbook"
extension-element-prefixes="str"
>
@ -30,10 +31,12 @@
<listitem>
<para>
<xsl:value-of disable-output-escaping="yes"
select="attr[@name = 'description']/string/@value" />
</para>
<nixos:option-description>
<para>
<xsl:value-of disable-output-escaping="yes"
select="attr[@name = 'description']/string/@value" />
</para>
</nixos:option-description>
<xsl:if test="attr[@name = 'type']">
<para>

View File

@ -0,0 +1,115 @@
<?xml version="1.0"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:str="http://exslt.org/strings"
xmlns:exsl="http://exslt.org/common"
xmlns:db="http://docbook.org/ns/docbook"
xmlns:nixos="tag:nixos.org"
extension-element-prefixes="str exsl">
<xsl:output method='xml' encoding="UTF-8" />
<xsl:template match="@*|node()">
<xsl:copy>
<xsl:apply-templates select="@*|node()" />
</xsl:copy>
</xsl:template>
<xsl:template name="break-up-description">
<xsl:param name="input" />
<xsl:param name="buffer" />
<!-- Every time we have two newlines following each other, we want to
break it into </para><para>. -->
<xsl:variable name="parbreak" select="'&#xa;&#xa;'" />
<!-- Similar to "(head:tail) = input" in Haskell. -->
<xsl:variable name="head" select="$input[1]" />
<xsl:variable name="tail" select="$input[position() &gt; 1]" />
<xsl:choose>
<xsl:when test="$head/self::text() and contains($head, $parbreak)">
<!-- If the haystack provided to str:split() directly starts or
ends with $parbreak, it doesn't generate a <token/> for that,
so we are doing this here. -->
<xsl:variable name="splitted-raw">
<xsl:if test="starts-with($head, $parbreak)"><token /></xsl:if>
<xsl:for-each select="str:split($head, $parbreak)">
<token><xsl:value-of select="node()" /></token>
</xsl:for-each>
<!-- Something like ends-with($head, $parbreak), but there is
no ends-with() in XSLT, so we need to use substring(). -->
<xsl:if test="
substring($head, string-length($head) -
string-length($parbreak) + 1) = $parbreak
"><token /></xsl:if>
</xsl:variable>
<xsl:variable name="splitted"
select="exsl:node-set($splitted-raw)/token" />
<!-- The buffer we had so far didn't contain any text nodes that
contain a $parbreak, so we can put the buffer along with the
first token of $splitted into a para element. -->
<para xmlns="http://docbook.org/ns/docbook">
<xsl:apply-templates select="exsl:node-set($buffer)" />
<xsl:apply-templates select="$splitted[1]/node()" />
</para>
<!-- We have already emitted the first splitted result, so the
last result is going to be set as the new $buffer later
because its contents may not be directly followed up by a
$parbreak. -->
<xsl:for-each select="$splitted[position() &gt; 1
and position() &lt; last()]">
<para xmlns="http://docbook.org/ns/docbook">
<xsl:apply-templates select="node()" />
</para>
</xsl:for-each>
<xsl:call-template name="break-up-description">
<xsl:with-param name="input" select="$tail" />
<xsl:with-param name="buffer" select="$splitted[last()]/node()" />
</xsl:call-template>
</xsl:when>
<!-- Either non-text node or one without $parbreak, which we just
want to buffer and continue recursing. -->
<xsl:when test="$input">
<xsl:call-template name="break-up-description">
<xsl:with-param name="input" select="$tail" />
<!-- This essentially appends $head to $buffer. -->
<xsl:with-param name="buffer">
<xsl:if test="$buffer">
<xsl:for-each select="exsl:node-set($buffer)">
<xsl:apply-templates select="." />
</xsl:for-each>
</xsl:if>
<xsl:apply-templates select="$head" />
</xsl:with-param>
</xsl:call-template>
</xsl:when>
<!-- No more $input, just put the remaining $buffer in a para. -->
<xsl:otherwise>
<para xmlns="http://docbook.org/ns/docbook">
<xsl:apply-templates select="exsl:node-set($buffer)" />
</para>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
<xsl:template match="nixos:option-description">
<xsl:choose>
<!--
Only process nodes that are comprised of a single <para/> element,
because if that's not the case the description already contains
</para><para> in between and we need no further processing.
-->
<xsl:when test="count(db:para) > 1">
<xsl:apply-templates select="node()" />
</xsl:when>
<xsl:otherwise>
<xsl:call-template name="break-up-description">
<xsl:with-param name="input"
select="exsl:node-set(db:para/node())" />
</xsl:call-template>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
</xsl:stylesheet>