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<div class="navheader"><table width="100%" summary="Navigation header"><tr><td width="20%" align="left"><a accesskey="p" href="code.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="deps.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a id="building"></a>Chapter 6. Building</h2></div></div></div><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><p>For most of this chapter, we will assume that you are
using a project <a class="link" href="getting_started.html" title="Chapter 2. Getting started">generated by Erlang.mk</a>
<a class="xref" href="getting_started.html" title="Chapter 2. Getting started">Chapter 2, <em>Getting started</em></a>.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="_how_to_build"></a>6.1. How to build</h2></div></div></div><p>To build a project, all you have to do is type <code class="literal">make</code>:</p><pre class="programlisting">$ make</pre><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><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 class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="_what_to_build"></a>6.2. What to build</h2></div></div></div><p>Erlang.mk gives you control over three steps of the build
process, allowing you to do a partial build if needed.</p><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><p>Erlang.mk handles those three phases automatically when you
type <code class="literal">make</code>. But sometimes you just want to repeat one or
two of them.</p><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 class="section"><div class="titlepage"><div><div><h3 class="title"><a id="_application"></a>6.2.1. Application</h3></div></div></div><p>You can build your application and dependencies without
generating a release by running the following command:</p><pre class="programlisting">$ make app</pre><p>To build your application without touching dependencies
at all, you can use the <code class="literal">SKIP_DEPS</code> variable:</p><pre class="programlisting">$ make app SKIP_DEPS=1</pre><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><p>Note that this command may fail if a required dependency
is missing.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="_dependencies"></a>6.2.2. Dependencies</h3></div></div></div><p>You can build all dependencies, and nothing else, by
running the following command:</p><pre class="programlisting">$ make deps</pre><p>This will fetch and compile all dependencies and their
dependencies, recursively.</p><p><a class="link" href="deps.html" title="Chapter 7. Packages and dependencies">Packages and dependencies</a>
<a class="xref" href="deps.html" title="Chapter 7. Packages and dependencies">Chapter 7, <em>Packages and dependencies</em></a> are covered
in the next chapter.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="_release"></a>6.2.3. Release</h3></div></div></div><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><p>To generate the release, <code class="literal">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><pre class="programlisting">$ make rel</pre><p>Consult the <a class="link" href="relx.html" title="Chapter 9. Releases">Releases</a>
<a class="xref" href="relx.html" title="Chapter 9. Releases">Chapter 9, <em>Releases</em></a> chapter for more
information about what releases are and how they are generated.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="_application_resource_file"></a>6.3. Application resource file</h2></div></div></div><p>When building your application, Erlang.mk will generate the
<a class="ulink" href="http://www.erlang.org/doc/man/app.html" target="_top">application resource file</a>.
This file is mandatory for all Erlang applications and is
found in <span class="emphasis"><em>ebin/$(PROJECT).app</em></span>.</p><p><code class="literal">PROJECT</code> is a variable defined in your Makefile and taken
from the name of the directory when Erlang.mk bootstraps
your project.</p><p>Erlang.mk can build the <span class="emphasis"><em>ebin/$(PROJECT).app</em></span> in two different
ways: from the configuration found in the Makefile, or from
the <span class="emphasis"><em>src/$(PROJECT).app.src</em></span> file.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="_application_configuration"></a>6.3.1. Application configuration</h3></div></div></div><p>Erlang.mk automatically fills the <code class="literal">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 class="variablelist"><dl class="variablelist"><dt><span class="term">
<code class="literal">PROJECT</code>
</span></dt><dd>
The name of the OTP application or library.
</dd><dt><span class="term">
<code class="literal">PROJECT_DESCRIPTION</code>
</span></dt><dd>
Short description of the project.
</dd><dt><span class="term">
<code class="literal">PROJECT_VERSION</code>
</span></dt><dd>
Current version of the project.
</dd><dt><span class="term">
<code class="literal">PROJECT_MOD</code>
</span></dt><dd>
The application callback module.
</dd><dt><span class="term">
<code class="literal">PROJECT_REGISTERED</code>
</span></dt><dd>
List of the names of all registered processes.
</dd><dt><span class="term">
<code class="literal">LOCAL_DEPS</code>
</span></dt><dd>
List of Erlang/OTP applications this project depends on,
excluding <code class="literal">erts</code>, <code class="literal">kernel</code> and <code class="literal">stdlib</code>, or list of
dependencies local to this repository (in <code class="literal">APPS_DIR</code>).
</dd><dt><span class="term">
<code class="literal">DEPS</code>
</span></dt><dd>
List of applications this project depends on that need
to be fetched by Erlang.mk.
</dd></dl></div><p>There’s no need for quotes or anything. The relevant part of
the Cowboy Makefile follows, if you need an example:</p><pre class="programlisting">PROJECT = cowboy
PROJECT_DESCRIPTION = Small, fast, modular HTTP server.
PROJECT_VERSION = 2.0.0-pre.2
PROJECT_REGISTERED = cowboy_clock
LOCAL_DEPS = crypto
DEPS = cowlib ranch</pre><p>Any space before and after the value is dropped.</p><p><a class="link" href="deps.html" title="Chapter 7. Packages and dependencies">Dependencies</a>
<a class="xref" href="deps.html" title="Chapter 7. Packages and dependencies">Chapter 7, <em>Packages and dependencies</em></a> are covered in details in
the next chapter.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="_legacy_method"></a>6.3.2. Legacy method</h3></div></div></div><p>The <span class="emphasis"><em>src/$(PROJECT).app.src</em></span> file is a legacy method of
building Erlang applications. It was introduced by the original
<code class="literal">rebar</code> build tool, of which Erlang.mk owes a great deal as it
is its main inspiration.</p><p>The <span class="emphasis"><em>.app.src</em></span> file serves as a template to generate the <span class="emphasis"><em>.app</em></span>
file. Erlang.mk will take it, fill in the <code class="literal">modules</code> value
dynamically, and save the result in <span class="emphasis"><em>ebin/$(PROJECT).app</em></span>.</p><p>When using this method, Erlang.mk cannot fill the <code class="literal">applications</code>
key from dependencies automatically, which means you need to
add them to Erlang.mk and to the <span class="emphasis"><em>.app.src</em></span> at the same time,
duplicating the work.</p><p>If you really can’t live without the legacy method, for one
reason or another, worry not; Erlang.mk will support it. And
if you need to create a new project that uses this method, you
just have to say so when bootstrapping:</p><pre class="programlisting">$ make -f erlang.mk bootstrap-lib LEGACY=1</pre></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="_automatic_application_resource_file_values"></a>6.4. Automatic application resource file values</h2></div></div></div><p>When building the application resource file, Erlang.mk may
automatically add an <code class="literal">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 class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
The application was built as a dependency of another, or
</li><li class="listitem">
The legacy method was used, and the <span class="emphasis"><em>.app.src</em></span> file contained <code class="literal">{id, "git"}</code>
</li></ul></div><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><pre class="programlisting">1> application:get_all_key(cowboy).
{ok,[{description,"Small, fast, modular HTTP server."},
{id,"2.0.0-pre.2-25-g0ffde50-dirty"},</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="_file_formats"></a>6.5. File formats</h2></div></div></div><p>Erlang.mk supports a variety of different source file formats.
The following formats are supported natively:</p><div class="informaltable"><table class="informaltable" cellpadding="4px" style="border-collapse: collapse;border-top: 3px solid #527bbd; border-bottom: 3px solid #527bbd; border-left: 3px solid #527bbd; border-right: 3px solid #527bbd; "><colgroup><col class="col_1" /><col class="col_2" /><col class="col_3" /><col class="col_4" /></colgroup><thead><tr><th style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="left" valign="top"> Extension </th><th style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"> Location </th><th style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"> Description </th><th style="border-bottom: 1px solid #527bbd; " align="center" valign="top"> Output</th></tr></thead><tbody><tr><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="left" valign="top"><p>.erl</p></td><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>src/</p></td><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>Erlang source</p></td><td style="border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>ebin/*.beam</p></td></tr><tr><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="left" valign="top"><p>.core</p></td><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>src/</p></td><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>Core Erlang source</p></td><td style="border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>ebin/*.beam</p></td></tr><tr><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="left" valign="top"><p>.xrl</p></td><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>src/</p></td><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>Leex source</p></td><td style="border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>src/*.erl</p></td></tr><tr><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="left" valign="top"><p>.yrl</p></td><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>src/</p></td><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>Yecc source</p></td><td style="border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>src/*.erl</p></td></tr><tr><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="left" valign="top"><p>.asn1</p></td><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>asn1/</p></td><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>ASN.1 files</p></td><td style="border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>include/<span class="strong"><strong>.hrl include/</strong></span>.asn1db src/*.erl</p></td></tr><tr><td style="border-right: 1px solid #527bbd; " align="left" valign="top"><p>.mib</p></td><td style="border-right: 1px solid #527bbd; " align="center" valign="top"><p>mibs/</p></td><td style="border-right: 1px solid #527bbd; " align="center" valign="top"><p>SNMP MIB files</p></td><td style="" align="center" valign="top"><p>include/<span class="strong"><strong>.hrl priv/mibs/</strong></span>.bin</p></td></tr></tbody></table></div><p>Files are always searched recursively.</p><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><p>In addition, Erlang.mk keeps track of header files (<code class="literal">.hrl</code>)
as described at the end of this chapter. It can also compile
C code, as described in the <a class="link" href="ports.html" title="Chapter 8. NIFs and port drivers">NIFs and port drivers</a>
<a class="xref" href="ports.html" title="Chapter 8. NIFs and port drivers">Chapter 8, <em>NIFs and port drivers</em></a>
chapter.</p><p>Erlang.mk also comes with plugins for the following formats:</p><div class="informaltable"><table class="informaltable" cellpadding="4px" style="border-collapse: collapse;border-top: 3px solid #527bbd; border-bottom: 3px solid #527bbd; border-left: 3px solid #527bbd; border-right: 3px solid #527bbd; "><colgroup><col class="col_1" /><col class="col_2" /><col class="col_3" /><col class="col_4" /></colgroup><thead><tr><th style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="left" valign="top"> Extension </th><th style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"> Location </th><th style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"> Description </th><th style="border-bottom: 1px solid #527bbd; " align="center" valign="top"> Output</th></tr></thead><tbody><tr><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="left" valign="top"><p>.dtl</p></td><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>templates/</p></td><td style="border-right: 1px solid #527bbd; border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>Django templates</p></td><td style="border-bottom: 1px solid #527bbd; " align="center" valign="top"><p>ebin/*.beam</p></td></tr><tr><td style="border-right: 1px solid #527bbd; " align="left" valign="top"><p>.proto</p></td><td style="border-right: 1px solid #527bbd; " align="center" valign="top"><p>src/</p></td><td style="border-right: 1px solid #527bbd; " align="center" valign="top"><p>Protocol buffers</p></td><td style="" align="center" valign="top"><p>ebin/*.beam</p></td></tr></tbody></table></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="_compilation_options"></a>6.6. Compilation options</h2></div></div></div><p>Erlang.mk provides a few variables that you can use to customize
the build process and the resulting files.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="_erlc_opts"></a>6.6.1. ERLC_OPTS</h3></div></div></div><p><code class="literal">ERLC_OPTS</code> can be used to pass some options to <code class="literal">erlc</code>, the Erlang
compiler. Erlang.mk does not restrict any option. Please refer to
the <a class="ulink" href="http://www.erlang.org/doc/man/erlc.html" target="_top">erlc Manual</a> for the
full list.</p><p>By default, Erlang.mk will set the following options:</p><pre class="programlisting">ERLC_OPTS = -Werror +debug_info +warn_export_vars +warn_shadow_vars +warn_obsolete_guard</pre><p>In other words: warnings as errors, debug info (recommended) and
enable warnings for exported variables, shadow variables and
obsolete guard functions.</p><p>You can redefine this variable in your Makefile to change it
completely, either before or after including Erlang.mk:</p><pre class="programlisting">ERLC_OPTS = +debug_info</pre><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 class="literal">:=</code> operator.</p><pre class="programlisting">include erlang.mk
ERLC_OPTS := $(filter-out -Werror,$(ERLC_OPTS))</pre></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="_erlc_exclude"></a>6.6.2. ERLC_EXCLUDE</h3></div></div></div><p><code class="literal">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><p>To exclude a module, simply list it in the variable, either
before or after including Erlang.mk:</p><pre class="programlisting">ERLC_EXCLUDE = cowboy_http2</pre></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="_cold_and_hot_builds"></a>6.7. Cold and hot builds</h2></div></div></div><p>The first time you run <code class="literal">make</code>, Erlang.mk will build everything.</p><p>The second time you run <code class="literal">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><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><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 class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="_dependency_tracking"></a>6.8. Dependency tracking</h2></div></div></div><div class="note" style="margin-left: 0; margin-right: 10%;"><h3 class="title">Note</h3><p>This section is about the dependency tracking between files
inside your project, not application dependencies.</p></div><p>Erlang.mk keeps track of the dependencies between the different
files in your project. This information is kept in the <span class="emphasis"><em>$(PROJECT).d</em></span>
file in your directory. It is generated if missing, and will be
generated again after every file change, by default.</p><p>Dependency tracking is what allows Erlang.mk to know when to
rebuild Erlang files when header files, behaviors or parse
transforms have changed. Erlang.mk also automatically keeps
track of which files should be compiled first, for example
when you have behaviors used by other modules in your project.</p><p>If your project is stable, you may want to disable generating
the dependency tracking file every time you compile. You can
do this by adding the following line to your <span class="emphasis"><em>Makefile</em></span>:</p><pre class="programlisting">NO_MAKEDEP ?= 1</pre><p>As you can see, the snippet above uses <code class="literal">?=</code> instead of a
simple equal sign. This is to allow you to temporarily override
this value when you do make substantial changes to your project
(including a new header file, new module with dependencies, etc.)
and want to rebuild the dependency tracking file. You’ll be
able to use the following command:</p><pre class="programlisting">$ NO_MAKEDEP= make</pre><p>Otherwise, <code class="literal">make clean app</code> will of course force the
recompilation of your project.</p><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 class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="_generating_erlang_source"></a>6.9. Generating Erlang source</h2></div></div></div><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 <span class="emphasis"><em>erlang.mk</em></span> file.</p><p>The easiest way is after:</p><pre class="programlisting">PROJECT = example
include erlang.mk
$(PROJECT).d:: src/generated_mod.erl
src/generated_mod.erl:: gen-mod.sh
$(gen_verbose) ./gen-mod.sh $@</pre><p>In this case we use <code class="literal">$(gen_verbose)</code> to hide the details of
the build by default. Erlang.mk will simply say what file
is it currently generating.</p><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><p>If for whatever reason you prefer to hook before including
Erlang.mk, don’t forget to set the <code class="literal">.DEFAULT_GOAL</code> variable,
otherwise nothing will get built:</p><pre class="programlisting">PROJECT = example
.DEFAULT_GOAL = all
$(PROJECT).d:: src/generated_mod.erl
include erlang.mk
src/generated_mod.erl:: gen-mod.sh
$(gen_verbose) ./gen-mod.sh $@</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="_cleaning"></a>6.10. Cleaning</h2></div></div></div><p>Building typically involves creating a lot of new files. Some
are reused in rebuilds, some are simply replaced. All can be
removed safely.</p><p>Erlang.mk provides two commands to remove them: <code class="literal">clean</code> and
<code class="literal">distclean</code>. <code class="literal">clean</code> removes all the intermediate files that
were created as a result of building, including the BEAM files,
the dependency tracking file and the generated documentation.
<code class="literal">distclean</code> removes these and more, including the downloaded
dependencies, Dialyzer’s PLT file and the generated release,
putting your directory back to the state it was before you
started working on it.</p><p>To clean:</p><pre class="programlisting">$ make clean</pre><p>Or distclean:</p><pre class="programlisting">$ make distclean</pre><p>That is the question.</p><p>Note that Erlang.mk will automatically clean some files as
part of other targets, but it will never run <code class="literal">distclean</code> if
you don’t explicitly use it.</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="code.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="code.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="deps.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> </td></tr></table></div>
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