path: root/en_US.ISO8859-1/books/fdp-primer/doc-build/chapter.sgml

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<chapter id="doc-build">
  <title>The Documentation Build Process</title>

  <para>This chapter's main purpose is to clearly explain <emphasis>how
    the documentation build process is organised</emphasis>, and
    <emphasis>how to affect modifications to this process</emphasis>.
    </para>

  <para>After you have finished reading this chapter you should:</para>

  <itemizedlist>
    <listitem>
      <para>Know what you need to build the FDP documentation, in
	addition to those mentioned in the <link
	linkend="tools">SGML tools chapter</link>.</para>
    </listitem>

    <listitem>
      <para>Be able to read and understand the
	<application>make</application> instructions that are present in
	each document's <filename>Makefile</filename>s, as well as an
	overview of the <filename>doc.project.mk</filename> includes.</para>
    </listitem>
 
    <listitem>
      <para>Be able to customize the build process by using
	<application>make</application> variables and
	<application>make</application> targets.</para>
    </listitem>
  </itemizedlist>

  <sect1>
    <title>The FreeBSD Documentation Build Toolset</title>

    <para>Here are your tools.  Use them every way you can.</para>

    <itemizedlist>
      <listitem>
	<para>The primary build tool you will need is
	  <application>make</application>, but specifically
	  <application>Berkeley Make</application>.</para>
      </listitem>

      <listitem>
	<para>Package building is handled by FreeBSD's
	  <application>pkg_create</application>.  If you are not using
	  FreeBSD, you will either have to live without packages, or
	  compile the source yourself.</para>
      </listitem>

      <listitem>
	<para><application>gzip</application> is needed to create
	  compressed versions of the document.
	  <application>bzip2</application> compression and
	  <application>zip</application> archives are also supported.
	  <application>tar</application> is supported, but package
	  building demands it.</para>
      </listitem>

      <listitem>
	<para><application>install</application> is the default method
	  to install the documentation.  There are alternatives,
	  however.</para
      </listitem>
    </itemizedlist>

    <note>
      <para>It is unlikely you will not be able to find these last two, they
	are mentioned for completeness.</para>
    </note>
  </sect1>

  <sect1>
    <title>Understanding Makefiles in the Documentation tree</title>

    <para>There are three main types of <filename>Makefile</filename>s 
      in the FreeBSD Documentation Project tree.</para>

    <itemizedlist>
      <listitem>
	<para><link linkend="sub-make">Subdirectory
	  <filename>Makefile</filename>s</link> simply pass
	  commands to those directories below them.</para>
      </listitem>

      <listitem>
	<para><link linkend="doc-make">Documentation
	  <filename>Makefile</filename>s</link> describe the
	  document(s) that should be produced from this directory.</para>
      </listitem>

      <listitem>
	<para><link linkend="make-includes"><application>Make</application>
	  includes</link> are the glue that perform the document production,
	  and are usually of the form
	  <filename>doc.<replaceable>xxx</replaceable>.mk</filename>.</para>
      </listitem>
    </itemizedlist>

    <para><application>Make</application> syntax is quickly revised as
      the we explore these types.</para>

    <sect2 id="sub-make">
      <title>Subdirectory Makefiles</title>

      <para>These directories usually take the form of:</para>

      <programlisting>SUBDIR =articles
SUBDIR+=books

COMPAT_SYMLINK = en

DOC_PREFIX?= ${.CURDIR}/..
.include "${DOC_PREFIX}/share/mk/doc.project.mk"</programlisting>

      <para>In quick summary, the first four non-empty lines define the
	<application>make</application> variables,
	<makevar>SUBDIR</makevar>, <makevar>COMPAT_SYMLINK</makevar>,
	and <makevar>DOC_PREFIX</makevar>.</para>

      <para>The first <makevar>SUBDIR</makevar> statement, as well as
	the <makevar>COMPAT_SYMLINK</makevar> statement, shows how to
	assign a value to a variable, overriding any previous
	value.</para>

      <para>The second <makevar>SUBDIR</makevar> statement shows how a
	value is appended to the current value of a variable.  The
	<makevar>SUBDIR</makevar> variable is now <literal>articles
	books</literal>.</para>

      <para>The <makevar>DOC_PREFIX</makevar> assignment shows how a
	value is assigned to the variable, but only if it is not already
	defined.  This is useful if <makevar>DOC_PREFIX</makevar> is not
	where this <filename>Makefile</filename> thinks it is - the user
	can override this and provide the correct value.</para>

      <para>Now what does it all mean?  <makevar>SUBDIR</makevar>
	mentions which subdirectories below this one the build process
	should pass any work on to.</para>

      <para><makevar>COMPAT_SYMLINK</makevar> is specific to
	compatibility symlinks (amazingly enough) for languages to their
	official encoding (<filename>doc/en</filename> would point to
	<filename>en_US.ISO-8859-1</filename>).</para>

      <para><makevar>DOC_PREFIX</makevar> is the path to the root of the
	FreeBSD Document Project tree.  This is not always that easy to
	find, and is also easily overridable, to allow for flexibility.
	<makevar>.CURDIR</makevar> is a <application>make</application>
	builtin variable with the path to the current directory.</para>

      <para>The final line includes the FreeBSD Documentation Project's
	project-wide <application>make</application> system file
	<filename>doc.project.mk</filename> which is the glue which
	converts these variables into build instructions.</para>

    </sect2>
    <sect2 id="doc-make">
      <title>Documentation Makefiles</title>

      <para>These <filename>Makefile</filename>s set a bunch of
	<application>make</application> variables that describe how to
	build the documentation contained in that directory.</para>

      <para>Here is an example:</para>

      <programlisting>MAINTAINER=nik@FreeBSD.org

DOC?= book

FORMATS?= html-split html

INSTALL_COMPRESSED?= gz
INSTALL_ONLY_COMPRESSED?=

# SGML content
SRCS=  book.sgml

DOC_PREFIX?= ${.CURDIR}/../../..

.include "$(DOC_PREFIX)/share/mk/docproj.docbook.mk"</programlisting>

      <para>The <makevar>MAINTAINER</makevar> variable is a very 
	important one.  This variable provides the ability to claim
	ownership over a document in the FreeBSD Documentation
	Project, whereby you gain the responsibility for maintaining 
	it.</para>

      <para><makevar>DOC</makevar> is the name (sans the
	<filename>.sgml</filename> extension) of the main document
	created by this directory.  <makevar>SRCS</makevar> lists all
	the individual files that make up the document.  This should
	also include important files in which a change should result
	in a rebuild.</para>

      <para><makevar>FORMATS</makevar> indicates the default formats
	that should be built for this document.
	<makevar>INSTALL_COMPRESSED</makevar> is the default list of
	compression techniques that should be used in the document
	build.  <makevar>INSTALL_ONLY_COMPRESS</makevar>, empty by
	default, should be non-empty if only compressed documents are
	desired in the build.</para>

      <note>
	<para>We covered optional variable assignments in the 
	  <link linkend="sub-make">previous section</link>.</para>
      </note>

      <para>The <makevar>DOC_PREFIX</makevar> and include statements
	should be familiar already.</para>
    </sect2>
  </sect1>

  <sect1 id="make-includes">
    <title>FreeBSD Documentation Project make includes</title>

    <para>This is best explained by inspection of the code.  Here are
      the system include files:</para>

    <itemizedlist>
      <listitem>
	<para><filename>doc.project.mk</filename> is the main project
	  include file, which includes all the following include files, as
	  necessary.</para>
      </listitem>

      <listitem>
	<para><filename>doc.subdir.mk</filename> handles traversing of
	  the document tree during the build and install processes.</para>
      </listitem>

      <listitem>
	<para><filename>doc.install.mk</filename> provides variables
	  that affect ownership and installation of documents.</para>
      </listitem>

      <listitem>
	<para><filename>doc.docbook.mk</filename> is included if
	  <makevar>DOCFORMAT</makevar> is <literal>docbook</literal>
	  and <makevar>DOC</makevar> is set.</para>
      </listitem>
    </itemizedlist>

    <sect2>
      <title>doc.project.mk</title>

      <para>By inspection:</para>

      <programlisting>DOCFORMAT?=	docbook
MAINTAINER?=	doc@FreeBSD.org

PREFIX?=	/usr/local
PRI_LANG?=	en_US.ISO8859-1

.if defined(DOC)
.if ${DOCFORMAT} == "docbook"
.include "doc.docbook.mk"
.endif
.endif

.include "doc.subdir.mk"
.include "doc.install.mk"</programlisting>

      <sect3>

	<title>Variables</title>

	<para><makevar>DOCFORMAT</makevar> and <makevar>MAINTAINER</makevar>
	  are assigned default values, if these are not set by the
	  document make file.</para>

	<para><makevar>PREFIX</makevar> is the prefix under which the
	  <link linkend="tools">documentation building tools</link> are
	  installed.  For normal package and port installation, this is
	  <filename>/usr/local</filename>.</para>

	<para><makevar>PRI_LANG</makevar> should be set to whatever
	  language and encoding is natural amongst users these documents are
	  being built for.  US English is the default.</para>

	<note>
	  <para><makevar>PRI_LANG</makevar> in no way affects what documents
	    can, or even will, be built.  It's main use is creating links to
	    commonly referenced documents into the FreeBSD documentation
	    install root.</para>
	</note>
      </sect3>

      <sect3>
	<title>Conditionals</title>
       
	<para>The <literal>.if defined(DOC)</literal> line is an example of
	  a <application>make</application> conditional which, like in
	  other programs, defines behaviour if some condition is true or
	  if it is false.  <literal>defined</literal> is a function which
	  returns whether the variable given is defined or not.</para>

	<para><literal>.if ${DOCFORMAT} == "docbook"</literal>, next,
	  tests whether the <makevar>DOCFORMAT</makevar> variable is
	  <literal>"docbook"</literal>, and in this case, includes
	  <filename>doc.docbook.mk</filename>.</para>

	<para>The two <literal>.endif</literal>s close the two above
	  conditionals, marking the end of their application.</para>
      </sect3>
    </sect2>

    <sect2>
      <title>doc.subdir.mk</title>

      <para>This is too long to explain by inspection, you should be
	able to work it out with the knowledge gained from the previous
	chapters, and a little help given here.</para>

      <sect3>
	<title>Variables</title>

	<itemizedlist>
	  <listitem>
	    <para><makevar>SUBDIR</makevar> is a list of subdirectories 
	      that the build process should go further down
	      into.</para>
	  </listitem>

	  <listitem>
	    <para><makevar>ROOT_SYMLINKS</makevar> is the name of
	      directories that should be linked to the document
	      install root from their actual locations, if the current
	      language is the primary language (specified by
	      <makevar>PRI_LANG</makevar>).</para>
	  </listitem>

	  <listitem>
	    <para><makevar>COMPAT_SYMLINK</makevar> is described in the
	      <link linkend="sub-make">Subdirectory Makefile</link>
	      section.</para>
	  </listitem>
	</itemizedlist>
      </sect3>

      <sect3>
	<title>Targets and macros</title>

	<para>Dependencies are described by 
	  <literal><replaceable>target</replaceable>:
	  <replaceable>dependency1 dependency2 ...</replaceable></literal>
	  tuples, where to build <literal>target</literal>, you need to build
	  the given dependencies first.</para>

	<para>After that descriptive tuple, instructions on how to build
	  the target may be given, if the conversion process between the
	  target and it's dependencies are not previously defined, or if
	  this particular conversion is not the same as the default
	  conversion method.</para>

	<para>A special dependency <literal>.USE</literal> defines
	  the equivalent of a macro.</para>

<programlisting>_SUBDIRUSE: .USE
.for entry in ${SUBDIR}
	@${ECHO} "===> ${DIRPRFX}${entry}"
	@(cd ${.CURDIR}/${entry} && \
	${MAKE} ${.TARGET:S/realpackage/package/:S/realinstall/install/} DIRPRFX=${DIRPRFX}${entry}/ )
.endfor</programlisting>

	<para>In the above, <maketarget>_SUBDIRUSE</maketarget> is now a
	  macro which will execute the given commands when it is listed
	  as a dependency.</para>

	<para>What sets this macro apart from other targets?  Basically,
	  it is executed <emphasis>after</emphasis> the instructions
	  given in the build procedure it is listed as a dependency to,
	  and it doesn't adjust <makevar>.TARGET</makevar>, which is the
	  variable which contains the name of the target currently
	  being built.</para>

<programlisting>clean: _SUBDIRUSE
	rm -f ${CLEANFILES}</programlisting>

	<para>In the above, <maketarget>clean</maketarget> will use the
	  <maketarget>_SUBDIRUSE</maketarget> macro after it has
	  executed the instruction 
	  <command>rm -f ${CLEANFILES}</command>.  In effect, this causes
	  <maketarget>clean</maketarget> to go further and further down
	  the directory tree, deleting built files as it goes
	  <emphasis>down</emphasis>, not on the way back up.</para>

	<sect4>
	  <title>Provided targets</title>

	  <itemizedlist>
	    <listitem>
	      <para><maketarget>install</maketarget> and
		<maketarget>package</maketarget> both go down the
		directory tree calling the real versions of themselves
		in the subdirectories.
		(<maketarget>realinstall</maketarget> and
		<maketarget>realpackage</maketarget>
		 respectively)</para>
	    </listitem>

	    <listitem>
	      <para><maketarget>clean</maketarget> removes files created
		by the build process (and goes down the directory tree
		too).  <maketarget>cleandir</maketarget> does the same,
		and also removes the object directory, if any.</para>
	    </listitem>
	  </itemizedlist>
	</sect4>
      </sect3>

      <sect3>
	<title>More on conditionals</title>

	<itemizedlist>
	  <listitem>
	    <para><literal>exists</literal> is another condition
	      function which returns true if the given file exists.</para>
	  </listitem>

	  <listitem>
	    <para><literal>empty</literal> returns true if the given
	      variable is empty.</para>
	  </listitem>

	  <listitem>
	    <para><literal>target</literal> returns true if the given
	      target does not already exist.</para>
	  </listitem>
	</itemizedlist>
      </sect3>

      <sect3>
	<title>Looping constructs in make (.for)</title>

	<para><literal>.for</literal> provides a way to repeat a set of
	  instructions for each space-seperated element in a variable.
	  It does this by assigning a variable to contain the current
	  element in the list being examined.</para>

<programlisting>_SUBDIRUSE: .USE
.for entry in ${SUBDIR}
	@${ECHO} "===> ${DIRPRFX}${entry}"
	@(cd ${.CURDIR}/${entry} && \
	${MAKE} ${.TARGET:S/realpackage/package/:S/realinstall/install/} DIRPRFX=${DIRPRFX}${entry}/ )
.endfor</programlisting>

	<para>In the above, if <makevar>SUBDIR</makevar> is empty, no
	  action is taken; if it has one or more elements, the
	  instructions between <literal>.for</literal> and
	  <literal>.endfor</literal> would repeat for every element,
	  with <makevar>entry</makevar> being replaced with the value of
	  the current element.</para>
      </sect3>
    </sect2>
  </sect1>
</chapter>

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