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|
<!DOCTYPE html>
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<meta name="author" content="Loïc Hoguin based on a design from (Soft10) Pol Cámara">
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<h1 class="lined-header"><span>Building</span></h1>
<div class="paragraph"><p>Erlang.mk can do a lot of things, but it is, first and
foremost, a build tool. In this chapter we will cover
the basics of building a project with Erlang.mk.</p></div>
<div class="paragraph"><p>For most of this chapter, we will assume that you are
using a project <a href="../getting_started">generated by Erlang.mk</a>.</p></div>
<div class="sect1">
<h2 id="_how_to_build">How to build</h2>
<div class="sectionbody">
<div class="paragraph"><p>To build a project, all you have to do is type <code>make</code>:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ make</tt></pre></div></div>
<div class="paragraph"><p>It will work regardless of your project: OTP applications,
library applications, NIFs, port drivers or even releases.
Erlang.mk also automatically downloads and compiles the
dependencies for your project.</p></div>
<div class="paragraph"><p>All this is possible thanks to a combination of configuration
and conventions. Most of the conventions come from Erlang/OTP
itself so any seasoned Erlang developers should feel right at
home.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_what_to_build">What to build</h2>
<div class="sectionbody">
<div class="paragraph"><p>Erlang.mk gives you control over three steps of the build
process, allowing you to do a partial build if needed.</p></div>
<div class="paragraph"><p>A build has three phases: first any dependency is fetched
and built, then the project itself is built and finally a
release may be generated when applicable. A release is only
generated for projects specifically configured to do so.</p></div>
<div class="paragraph"><p>Erlang.mk handles those three phases automatically when you
type <code>make</code>. But sometimes you just want to repeat one or
two of them.</p></div>
<div class="paragraph"><p>The commands detailed in this section are most useful after
you have a successful build as they allow you to quickly
redo a step instead of going through everything. This is
especially useful for large projects or projects that end
up generating releases.</p></div>
<div class="sect3">
<h4 id="_application">Application</h4>
<div class="paragraph"><p>You can build your application and dependencies without
generating a release by running the following command:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ make app</tt></pre></div></div>
<div class="paragraph"><p>To build your application without touching dependencies
at all, you can use the <code>SKIP_DEPS</code> variable:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ make app <span style="color: #009900">SKIP_DEPS</span><span style="color: #990000">=</span><span style="color: #993399">1</span></tt></pre></div></div>
<div class="paragraph"><p>This command is very useful if you have a lot of dependencies
and develop on a machine with slow file access, like the
Raspberry Pi and many other embedded devices.</p></div>
<div class="paragraph"><p>Note that this command may fail if a required dependency
is missing.</p></div>
</div>
<div class="sect3">
<h4 id="_dependencies">Dependencies</h4>
<div class="paragraph"><p>You can build all dependencies, and nothing else, by
running the following command:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ make deps</tt></pre></div></div>
<div class="paragraph"><p>This will fetch and compile all dependencies and their
dependencies, recursively.</p></div>
<div class="paragraph"><p><a href="../deps">Packages and dependencies</a> are covered
in the next chapter.</p></div>
</div>
<div class="sect3">
<h4 id="_release">Release</h4>
<div class="paragraph"><p>It is not possible to build the release without at least
building the application itself, unless of course if there’s
no application to begin with.</p></div>
<div class="paragraph"><p>To generate the release, <code>make</code> will generally suffice with
a normal Erlang.mk. A separate target is however available,
and will take care of building the release, after building
the application and all dependencies:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ make rel</tt></pre></div></div>
<div class="paragraph"><p>Consult the <a href="../relx">Releases</a> chapter for more
information about what releases are and how they are generated.</p></div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_application_resource_file">Application resource file</h2>
<div class="sectionbody">
<div class="paragraph"><p>When building your application, Erlang.mk will generate the
<a href="http://www.erlang.org/doc/man/app.html">application resource file</a>.
This file is mandatory for all Erlang applications and is
found in <em>ebin/$(PROJECT).app</em>.</p></div>
<div class="paragraph"><p><code>PROJECT</code> is a variable defined in your Makefile and taken
from the name of the directory when Erlang.mk bootstraps
your project.</p></div>
<div class="paragraph"><p>Erlang.mk can build the <em>ebin/$(PROJECT).app</em> in two different
ways: from the configuration found in the Makefile, or from
the <em>src/$(PROJECT).app.src</em> file.</p></div>
<div class="sect3">
<h4 id="_application_configuration">Application configuration</h4>
<div class="paragraph"><p>Erlang.mk automatically fills the <code>PROJECT</code> variable when
bootstrapping a new project, but everything else is up to
you. None of the values are required to build your project,
although it is recommended to fill everything relevant to
your situation.</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
<code>PROJECT</code>
</dt>
<dd>
<p>
The name of the OTP application or library.
</p>
</dd>
<dt class="hdlist1">
<code>PROJECT_DESCRIPTION</code>
</dt>
<dd>
<p>
Short description of the project.
</p>
</dd>
<dt class="hdlist1">
<code>PROJECT_VERSION</code>
</dt>
<dd>
<p>
Current version of the project.
</p>
</dd>
<dt class="hdlist1">
<code>PROJECT_MOD</code>
</dt>
<dd>
<p>
The application callback module.
</p>
</dd>
<dt class="hdlist1">
<code>PROJECT_REGISTERED</code>
</dt>
<dd>
<p>
List of the names of all registered processes.
</p>
</dd>
<dt class="hdlist1">
<code>PROJECT_ENV</code>
</dt>
<dd>
<p>
Configuration parameters used by the application.
</p>
</dd>
<dt class="hdlist1">
<code>PROJECT_APP_EXTRA_KEYS</code>
</dt>
<dd>
<p>
Other keys you want to add to the application <code>.app</code> file.
The variable content is written as-is to the <code>.app</code> file,
so be sure to format valid Erlang terms. For example:
<code>PROJECT_APP_EXTRA_KEYS = {maxT, 10000}, {start_phases, [...]}</code>.
</p>
</dd>
<dt class="hdlist1">
<code>LOCAL_DEPS</code>
</dt>
<dd>
<p>
List of Erlang/OTP applications this project depends on,
excluding <code>erts</code>, <code>kernel</code> and <code>stdlib</code>, or list of
dependencies local to this repository (in <code>APPS_DIR</code>).
</p>
</dd>
<dt class="hdlist1">
<code>DEPS</code>
</dt>
<dd>
<p>
List of applications this project depends on that need
to be fetched by Erlang.mk.
</p>
</dd>
</dl></div>
<div class="paragraph"><p>There’s no need for quotes or anything. The relevant part of
the Cowboy Makefile follows, if you need an example:</p></div>
<div class="listingblock">
<div class="content"></div></div>
<div class="paragraph"><p>Any space before and after the value is dropped.</p></div>
<div class="paragraph"><p><a href="../deps">Dependencies</a> are covered in details in
the next chapter.</p></div>
</div>
<div class="sect3">
<h4 id="_legacy_method">Legacy method</h4>
<div class="paragraph"><p>The <em>src/$(PROJECT).app.src</em> file is a legacy method of
building Erlang applications. It was introduced by the original
<code>rebar</code> build tool, of which Erlang.mk owes a great deal as it
is its main inspiration.</p></div>
<div class="paragraph"><p>The <em>.app.src</em> file serves as a template to generate the <em>.app</em>
file. Erlang.mk will take it, fill in the <code>modules</code> value
dynamically, and save the result in <em>ebin/$(PROJECT).app</em>.</p></div>
<div class="paragraph"><p>When using this method, Erlang.mk cannot fill the <code>applications</code>
key from dependencies automatically, which means you need to
add them to Erlang.mk and to the <em>.app.src</em> at the same time,
duplicating the work.</p></div>
<div class="paragraph"><p>If you really can’t live without the legacy method, for one
reason or another, worry not; Erlang.mk will support it. And
if you need to create a new project that uses this method, you
just have to say so when bootstrapping:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ make -f erlang<span style="color: #990000">.</span>mk bootstrap-lib <span style="color: #009900">LEGACY</span><span style="color: #990000">=</span><span style="color: #993399">1</span></tt></pre></div></div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_automatic_application_resource_file_values">Automatic application resource file values</h2>
<div class="sectionbody">
<div class="paragraph"><p>When building the application resource file, Erlang.mk may
automatically add an <code>id</code> key with information about the
Git commit (if using Git), or an empty string otherwise.
It will only do this under specific conditions:</p></div>
<div class="ulist"><ul>
<li>
<p>
The application was built as a dependency of another, or
</p>
</li>
<li>
<p>
The legacy method was used, and the <em>.app.src</em> file contained <code>{id, "git"}</code>
</p>
</li>
</ul></div>
<div class="paragraph"><p>This value is most useful when you need to help your users,
as it allows you to know which version they run exactly by
asking them to look in the file, or by running a simple
command on their production server:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #993399">1</span><span style="color: #990000">></span> <span style="font-weight: bold"><span style="color: #000000">application:get_all_key</span></span>(<span style="color: #FF6600">cowboy</span>)<span style="color: #990000">.</span>
{<span style="color: #FF6600">ok</span>,[{<span style="color: #FF6600">description</span>,<span style="color: #FF0000">"Small, fast, modular HTTP server."</span>},
{<span style="color: #FF6600">id</span>,<span style="color: #FF0000">"2.0.0-pre.2-25-g0ffde50-dirty"</span>},</tt></pre></div></div>
</div>
</div>
<div class="sect1">
<h2 id="_file_formats">File formats</h2>
<div class="sectionbody">
<div class="paragraph"><p>Erlang.mk supports a variety of different source file formats.
The following formats are supported natively:</p></div>
<div class="tableblock">
<table rules="all"
width="100%"
frame="border"
cellspacing="0" cellpadding="4">
<col width="25%" />
<col width="25%" />
<col width="25%" />
<col width="25%" />
<thead>
<tr>
<th align="left" valign="top"> Extension </th>
<th align="center" valign="top"> Location </th>
<th align="center" valign="top"> Description </th>
<th align="center" valign="top"> Output</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left" valign="top"><p class="table">.erl</p></td>
<td align="center" valign="top"><p class="table">src/</p></td>
<td align="center" valign="top"><p class="table">Erlang source</p></td>
<td align="center" valign="top"><p class="table">ebin/*.beam</p></td>
</tr>
<tr>
<td align="left" valign="top"><p class="table">.core</p></td>
<td align="center" valign="top"><p class="table">src/</p></td>
<td align="center" valign="top"><p class="table">Core Erlang source</p></td>
<td align="center" valign="top"><p class="table">ebin/*.beam</p></td>
</tr>
<tr>
<td align="left" valign="top"><p class="table">.xrl</p></td>
<td align="center" valign="top"><p class="table">src/</p></td>
<td align="center" valign="top"><p class="table">Leex source</p></td>
<td align="center" valign="top"><p class="table">src/*.erl</p></td>
</tr>
<tr>
<td align="left" valign="top"><p class="table">.yrl</p></td>
<td align="center" valign="top"><p class="table">src/</p></td>
<td align="center" valign="top"><p class="table">Yecc source</p></td>
<td align="center" valign="top"><p class="table">src/*.erl</p></td>
</tr>
<tr>
<td align="left" valign="top"><p class="table">.asn1</p></td>
<td align="center" valign="top"><p class="table">asn1/</p></td>
<td align="center" valign="top"><p class="table">ASN.1 files</p></td>
<td align="center" valign="top"><p class="table">include/<strong>.hrl include/</strong>.asn1db src/*.erl</p></td>
</tr>
<tr>
<td align="left" valign="top"><p class="table">.mib</p></td>
<td align="center" valign="top"><p class="table">mibs/</p></td>
<td align="center" valign="top"><p class="table">SNMP MIB files</p></td>
<td align="center" valign="top"><p class="table">include/<strong>.hrl priv/mibs/</strong>.bin</p></td>
</tr>
</tbody>
</table>
</div>
<div class="paragraph"><p>Files are always searched recursively.</p></div>
<div class="paragraph"><p>The build is ordered, so that files that generate Erlang source
files are run before, and the resulting Erlang source files are
then built normally.</p></div>
<div class="paragraph"><p>In addition, Erlang.mk keeps track of header files (<code>.hrl</code>)
as described at the end of this chapter. It can also compile
C code, as described in the <a href="../ports">NIFs and port drivers</a>
chapter.</p></div>
<div class="paragraph"><p>Erlang.mk also comes with plugins for the following formats:</p></div>
<div class="tableblock">
<table rules="all"
width="100%"
frame="border"
cellspacing="0" cellpadding="4">
<col width="25%" />
<col width="25%" />
<col width="25%" />
<col width="25%" />
<thead>
<tr>
<th align="left" valign="top"> Extension </th>
<th align="center" valign="top"> Location </th>
<th align="center" valign="top"> Description </th>
<th align="center" valign="top"> Output</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left" valign="top"><p class="table">.dtl</p></td>
<td align="center" valign="top"><p class="table">templates/</p></td>
<td align="center" valign="top"><p class="table">Django templates</p></td>
<td align="center" valign="top"><p class="table">ebin/*.beam</p></td>
</tr>
<tr>
<td align="left" valign="top"><p class="table">.proto</p></td>
<td align="center" valign="top"><p class="table">src/</p></td>
<td align="center" valign="top"><p class="table">Protocol buffers</p></td>
<td align="center" valign="top"><p class="table">ebin/*.beam</p></td>
</tr>
</tbody>
</table>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_compilation_options">Compilation options</h2>
<div class="sectionbody">
<div class="paragraph"><p>Erlang.mk provides a few variables that you can use to customize
the build process and the resulting files.</p></div>
<div class="sect3">
<h4 id="_erlc_opts">ERLC_OPTS</h4>
<div class="paragraph"><p><code>ERLC_OPTS</code> can be used to pass some options to <code>erlc</code>, the Erlang
compiler. Erlang.mk does not restrict any option. Please refer to
the <a href="http://www.erlang.org/doc/man/erlc.html">erlc Manual</a> for the
full list.</p></div>
<div class="paragraph"><p>By default, Erlang.mk will set the following options:</p></div>
<div class="listingblock">
<div class="content"></div></div>
<div class="paragraph"><p>In other words: warnings as errors, debug info (recommended) and
enable warnings for exported variables, shadow variables and
obsolete guard functions.</p></div>
<div class="paragraph"><p>You can redefine this variable in your Makefile to change it
completely, either before or after including Erlang.mk:</p></div>
<div class="listingblock">
<div class="content"></div></div>
<div class="paragraph"><p>You can also filter out some options from the defaults Erlang.mk
sets, by defining ERLC_OPTS after including Erlang.mk using the
<code>:=</code> operator.</p></div>
<div class="listingblock">
<div class="content"></div></div>
</div>
<div class="sect3">
<h4 id="_erlc_asn1_opts">ERLC_ASN1_OPTS</h4>
<div class="paragraph"><p><code>ERLC_ASN1_OPTS</code> can be used to pass compiler options when compiling
ASN.1 files. Please refer to the
<a href="http://erlang.org/doc/man/asn1ct.html">asn1ct manual</a> for the full list.</p></div>
<div class="paragraph"><p>By default, Erlang.mk will leave this empty.</p></div>
<div class="paragraph"><p>You can redefine this variable in your Makefile.
Please see the <code>ERLC_OPTS</code> section for instructions.</p></div>
</div>
<div class="sect3">
<h4 id="_erlc_exclude">ERLC_EXCLUDE</h4>
<div class="paragraph"><p><code>ERLC_EXCLUDE</code> can be used to exclude some modules from the
compilation. It’s there for handling special cases, you should
not normally need it.</p></div>
<div class="paragraph"><p>To exclude a module, simply list it in the variable, either
before or after including Erlang.mk:</p></div>
<div class="listingblock">
<div class="content"></div></div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_cold_and_hot_builds">Cold and hot builds</h2>
<div class="sectionbody">
<div class="paragraph"><p>The first time you run <code>make</code>, Erlang.mk will build everything.</p></div>
<div class="paragraph"><p>The second time you run <code>make</code>, and all subsequent times, Erlang.mk
will only rebuild what changed. Erlang.mk has been optimized for
this use case, as it is the most common during development.</p></div>
<div class="paragraph"><p>Erlang.mk figures out what changed by using the dependency tracking
feature of Make. Make automatically rebuilds a target if one of its
dependency has changed (for example if a header file has changed,
all the source files that include it will be rebuilt), and Erlang.mk
leverages this feature to cut down on rebuild times.</p></div>
<div class="paragraph"><p>Note that this applies only to building; some other features of
Erlang.mk will run every time they are called regardless of files
changed.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_dependency_tracking">Dependency tracking</h2>
<div class="sectionbody">
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">This section is about the dependency tracking between files
inside your project, not application dependencies.</td>
</tr></table>
</div>
<div class="paragraph"><p>Erlang.mk keeps track of the dependencies between the different
files in your project. This information is kept in the <em>$(PROJECT).d</em>
file in your directory. It is generated if missing, and will be
generated again after every file change, by default.</p></div>
<div class="paragraph"><p>Dependency tracking is what allows Erlang.mk to know when to
rebuild Erlang files when header files, behaviors or parse
transforms have changed. Erlang.mk also automatically keeps
track of which files should be compiled first, for example
when you have behaviors used by other modules in your project.</p></div>
<div class="paragraph"><p>If your project is stable, you may want to disable generating
the dependency tracking file every time you compile. You can
do this by adding the following line to your <em>Makefile</em>:</p></div>
<div class="listingblock">
<div class="content"></div></div>
<div class="paragraph"><p>As you can see, the snippet above uses <code>?=</code> instead of a
simple equal sign. This is to allow you to temporarily override
this value when you do make substantial changes to your project
(including a new header file, new module with dependencies, etc.)
and want to rebuild the dependency tracking file. You’ll be
able to use the following command:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ <span style="color: #009900">NO_MAKEDEP</span><span style="color: #990000">=</span> make</tt></pre></div></div>
<div class="paragraph"><p>Otherwise, <code>make clean app</code> will of course force the
recompilation of your project.</p></div>
<div class="paragraph"><p>Erlang.mk can also keep track of the source files generated
by other means, for example if you generate code from a data
file in your repository.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_generating_erlang_source">Generating Erlang source</h2>
<div class="sectionbody">
<div class="paragraph"><p>Erlang.mk provides hooks at different stages of the build process.
When your goal is to generate Erlang source files, you can
add your own rules before or after the dependency tracking
file is generated. To do this, you would add your hook before
or after including the <em>erlang.mk</em> file.</p></div>
<div class="paragraph"><p>The easiest way is after:</p></div>
<div class="listingblock">
<div class="content"></div></div>
<div class="paragraph"><p>In this case we use <code>$(gen_verbose)</code> to hide the details of
the build by default. Erlang.mk will simply say what file
is it currently generating.</p></div>
<div class="paragraph"><p>When using an external script to generate the Erlang source
file, it is recommended to depend on that script, so that
the source file gets generated again when the script gets
modified.</p></div>
<div class="paragraph"><p>If for whatever reason you prefer to hook before including
Erlang.mk, don’t forget to set the <code>.DEFAULT_GOAL</code> variable,
otherwise nothing will get built:</p></div>
<div class="listingblock">
<div class="content"></div></div>
</div>
</div>
<div class="sect1">
<h2 id="_cleaning">Cleaning</h2>
<div class="sectionbody">
<div class="paragraph"><p>Building typically involves creating a lot of new files. Some
are reused in rebuilds, some are simply replaced. All can be
removed safely.</p></div>
<div class="paragraph"><p>Erlang.mk provides two commands to remove them: <code>clean</code> and
<code>distclean</code>. <code>clean</code> removes all the intermediate files that
were created as a result of building, including the BEAM files,
the dependency tracking file and the generated documentation.
<code>distclean</code> removes these and more, including the downloaded
dependencies, Dialyzer’s PLT file and the generated release,
putting your directory back to the state it was before you
started working on it.</p></div>
<div class="paragraph"><p>To clean:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ make clean</tt></pre></div></div>
<div class="paragraph"><p>Or distclean:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 3.1.8
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ make distclean</tt></pre></div></div>
<div class="paragraph"><p>That is the question.</p></div>
<div class="paragraph"><p>Note that Erlang.mk will automatically clean some files as
part of other targets, but it will never run <code>distclean</code> if
you don’t explicitly use it.</p></div>
</div>
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