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<section xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xml:id="sec-bower">
<title>Bower</title>
<para>
<link xlink:href="http://bower.io">Bower</link> is a package manager for web
site front-end components. Bower packages (comprising of build artefacts and
sometimes sources) are stored in <command>git</command> repositories,
typically on Github. The package registry is run by the Bower team with
package metadata coming from the <filename>bower.json</filename> file within
each package.
</para>
<para>
The end result of running Bower is a <filename>bower_components</filename>
directory which can be included in the web app's build process.
</para>
<para>
Bower can be run interactively, by installing
<varname>nodePackages.bower</varname>. More interestingly, the Bower
components can be declared in a Nix derivation, with the help of
<varname>nodePackages.bower2nix</varname>.
</para>
<section xml:id="ssec-bower2nix-usage">
<title><command>bower2nix</command> usage</title>
<para>
Suppose you have a <filename>bower.json</filename> with the following
contents:
<example xml:id="ex-bowerJson">
<title><filename>bower.json</filename></title>
<programlisting language="json">
<![CDATA[{
"name": "my-web-app",
"dependencies": {
"angular": "~1.5.0",
"bootstrap": "~3.3.6"
}
}]]>
</programlisting>
</example>
</para>
<para>
Running <command>bower2nix</command> will produce something like the
following output:
<programlisting language="nix">
<![CDATA[{ fetchbower, buildEnv }:
buildEnv { name = "bower-env"; ignoreCollisions = true; paths = [
(fetchbower "angular" "1.5.3" "~1.5.0" "1749xb0firxdra4rzadm4q9x90v6pzkbd7xmcyjk6qfza09ykk9y")
(fetchbower "bootstrap" "3.3.6" "~3.3.6" "1vvqlpbfcy0k5pncfjaiskj3y6scwifxygfqnw393sjfxiviwmbv")
(fetchbower "jquery" "2.2.2" "1.9.1 - 2" "10sp5h98sqwk90y4k6hbdviwqzvzwqf47r3r51pakch5ii2y7js1")
]; }]]>
</programlisting>
</para>
<para>
Using the <command>bower2nix</command> command line arguments, the output
can be redirected to a file. A name like
<filename>bower-packages.nix</filename> would be fine.
</para>
<para>
The resulting derivation is a union of all the downloaded Bower packages
(and their dependencies). To use it, they still need to be linked together
by Bower, which is where <varname>buildBowerComponents</varname> is useful.
</para>
</section>
<section xml:id="ssec-build-bower-components">
<title><varname>buildBowerComponents</varname> function</title>
<para>
The function is implemented in
<link xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/bower-modules/generic/default.nix">
<filename>pkgs/development/bower-modules/generic/default.nix</filename></link>.
Example usage:
<example xml:id="ex-buildBowerComponents">
<title>buildBowerComponents</title>
<programlisting language="nix">
bowerComponents = buildBowerComponents {
name = "my-web-app";
generated = ./bower-packages.nix; <co xml:id="ex-buildBowerComponents-1" />
src = myWebApp; <co xml:id="ex-buildBowerComponents-2" />
};
</programlisting>
</example>
</para>
<para>
In <xref linkend="ex-buildBowerComponents" />, the following arguments are
of special significance to the function:
<calloutlist>
<callout arearefs="ex-buildBowerComponents-1">
<para>
<varname>generated</varname> specifies the file which was created by
<command>bower2nix</command>.
</para>
</callout>
<callout arearefs="ex-buildBowerComponents-2">
<para>
<varname>src</varname> is your project's sources. It needs to contain a
<filename>bower.json</filename> file.
</para>
</callout>
</calloutlist>
</para>
<para>
<varname>buildBowerComponents</varname> will run Bower to link together the
output of <command>bower2nix</command>, resulting in a
<filename>bower_components</filename> directory which can be used.
</para>
<para>
Here is an example of a web frontend build process using
<command>gulp</command>. You might use <command>grunt</command>, or anything
else.
</para>
<example xml:id="ex-bowerGulpFile">
<title>Example build script (<filename>gulpfile.js</filename>)</title>
<programlisting language="javascript">
<![CDATA[var gulp = require('gulp');
gulp.task('default', [], function () {
gulp.start('build');
});
gulp.task('build', [], function () {
console.log("Just a dummy gulp build");
gulp
.src(["./bower_components/**/*"])
.pipe(gulp.dest("./gulpdist/"));
});]]>
</programlisting>
</example>
<example xml:id="ex-buildBowerComponentsDefaultNix">
<title>Full example — <filename>default.nix</filename></title>
<programlisting language="nix">
{ myWebApp ? { outPath = ./.; name = "myWebApp"; }
, pkgs ? import <nixpkgs> {}
}:
pkgs.stdenv.mkDerivation {
name = "my-web-app-frontend";
src = myWebApp;
buildInputs = [ pkgs.nodePackages.gulp ];
bowerComponents = pkgs.buildBowerComponents { <co xml:id="ex-buildBowerComponentsDefault-1" />
name = "my-web-app";
generated = ./bower-packages.nix;
src = myWebApp;
};
buildPhase = ''
cp --reflink=auto --no-preserve=mode -R $bowerComponents/bower_components . <co xml:id="ex-buildBowerComponentsDefault-2" />
export HOME=$PWD <co xml:id="ex-buildBowerComponentsDefault-3" />
${pkgs.nodePackages.gulp}/bin/gulp build <co xml:id="ex-buildBowerComponentsDefault-4" />
'';
installPhase = "mv gulpdist $out";
}
</programlisting>
</example>
<para>
A few notes about <xref linkend="ex-buildBowerComponentsDefaultNix" />:
<calloutlist>
<callout arearefs="ex-buildBowerComponentsDefault-1">
<para>
The result of <varname>buildBowerComponents</varname> is an input to the
frontend build.
</para>
</callout>
<callout arearefs="ex-buildBowerComponentsDefault-2">
<para>
Whether to symlink or copy the <filename>bower_components</filename>
directory depends on the build tool in use. In this case a copy is used
to avoid <command>gulp</command> silliness with permissions.
</para>
</callout>
<callout arearefs="ex-buildBowerComponentsDefault-3">
<para>
<command>gulp</command> requires <varname>HOME</varname> to refer to a
writeable directory.
</para>
</callout>
<callout arearefs="ex-buildBowerComponentsDefault-4">
<para>
The actual build command. Other tools could be used.
</para>
</callout>
</calloutlist>
</para>
</section>
<section xml:id="ssec-bower2nix-troubleshooting">
<title>Troubleshooting</title>
<variablelist>
<varlistentry>
<term>
<literal>ENOCACHE</literal> errors from <varname>buildBowerComponents</varname>
</term>
<listitem>
<para>
This means that Bower was looking for a package version which doesn't
exist in the generated <filename>bower-packages.nix</filename>.
</para>
<para>
If <filename>bower.json</filename> has been updated, then run
<command>bower2nix</command> again.
</para>
<para>
It could also be a bug in <command>bower2nix</command> or
<command>fetchbower</command>. If possible, try reformulating the version
specification in <filename>bower.json</filename>.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
</section>
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