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erlang support: Add minimal documentation to nix

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This commit adds some very minimial documentation to the Nix
manual. Hopefully, its enough to get someone started and serve as a
first footstep for future documentation writers
This commit is contained in:
Eric Merritt 2016-01-10 17:51:43 -08:00
parent 4ed5836dd3
commit 6a493a2b43
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<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xml:id="users-guide-to-the-erlang-infrastructure">
<title>User's Guide to the Erlang Infrastructure</title>
<section xml:id="how-to-install-erlang-packages">
<title>How to install Erlang packages</title>
<para>
Erlang packages are not registered in the top level simply because
they are not relevant to the vast majority of Nix users. They are
installable using the <literal>erlangPackages</literal> attribute set.
You can list the avialable packages in the
<literal>erlangPackages</literal> with the following command:
</para>
<programlisting>
$ nix-env -f &quot;&lt;nixpkgs&gt;&quot; -qaP -A erlangPackages
erlangPackages.esqlite esqlite-0.2.1
erlangPackages.goldrush goldrush-0.1.7
erlangPackages.ibrowse ibrowse-4.2.2
erlangPackages.jiffy jiffy-0.14.5
erlangPackages.lager lager-3.0.2
erlangPackages.meck meck-0.8.3
erlangPackages.rebar3-pc pc-1.1.0
</programlisting>
<para>
To install any of those packages into your profile, refer to them by
their attribute path (first column):
</para>
<programlisting>
$ nix-env -f &quot;&lt;nixpkgs&gt;&quot; -iA erlangPackages.ibrowse
</programlisting>
<para>
The attribute path of any Erlang packages corresponds to the name
of that particular package in Hex or its OTP Application/Release name.
</para>
</section>
<section xml:id="packaging-erlang-applications">
<title>Packaging Erlang Applications</title>
<section xml:id="rebar3-packages">
<title>Rebar3 Packages</title>
<para>
There is a Nix functional called
<literal>buildRebar3</literal>. We use this function to make a
derivation that understands how to build the rebar3 project. For
example, the epression we use to build the <link
xlink:href="https://github.com/erlang-nix/hex2nix">hex2nix</link>
project follows.
</para>
<programlisting>
{stdenv, fetchFromGitHub, buildRebar3, ibrowse, jsx, erlware_commons }:
buildRebar3 rec {
name = "hex2nix";
version = "0.0.1";
src = fetchFromGitHub {
owner = "ericbmerritt";
repo = "hex2nix";
rev = "${version}";
sha256 = "1w7xjidz1l5yjmhlplfx7kphmnpvqm67w99hd2m7kdixwdxq0zqg";
};
erlangDeps = [ ibrowse jsx erlware_commons ];
}
</programlisting>
<para>
The only visible difference between this derivation and
something like <literal>stdenv.mkDerivation</literal> is that we
have added <literal>erlangDeps</literal> to the derivation. If
you add your Erlang dependencies here they will be correctly
handled by the system.
</para>
<para>
If your package needs to compile native code via Rebar's port
compilation mechenism. You should add <literal>compilePort =
true;</literal> to the derivation.
</para>
</section>
<section xml:id="hex-packages">
<title>Hex Packages</title>
<para>
Hex packages are based on Rebar packages. In fact, at the moment
we can only compile Hex packages that are buildable with
Rebar3. Packages that use Mix and other build systems are not
supported. That being said, we know a lot more about Hex and can
do more for you.
</para>
<programlisting>
{ buildHex }:
buildHex {
name = "esqlite";
version = "0.2.1";
sha256 = "1296fn1lz4lz4zqzn4dwc3flgkh0i6n4sydg501faabfbv8d3wkr";
compilePort = true;
}
</programlisting>
<para>
For Hex packages you need to provide the name, the version, and
the Sha 256 digest of the package and use
<literal>buildHex</literal> to build it. Obviously, the package
needs to have already been published to Hex.
</para>
</section>
</section>
<section xml:id="how-to-develop">
<title>How to develop</title>
<section xml:id="accessing-an-environment">
<title>Accessing an Environment</title>
<para>
Often, all you want to do is be able to access a valid
environment that contains a specific package and its
dependencies. we can do that with the <literal>env</literal>
part of a derivation. For example, lets say we want to access an
erlang repl with ibrowse loaded up. We could do the following.
</para>
<programlisting>
~/w/nixpkgs ❯❯❯ nix-shell -A erlangPackages.ibrowse.env --run "erl"
Erlang/OTP 18 [erts-7.0] [source] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false]
Eshell V7.0 (abort with ^G)
1> m(ibrowse).
Module: ibrowse
MD5: 3b3e0137d0cbb28070146978a3392945
Compiled: January 10 2016, 23:34
Object file: /nix/store/g1rlf65rdgjs4abbyj4grp37ry7ywivj-ibrowse-4.2.2/lib/erlang/lib/ibrowse-4.2.2/ebin/ibrowse.beam
Compiler options: [{outdir,"/tmp/nix-build-ibrowse-4.2.2.drv-0/hex-source-ibrowse-4.2.2/_build/default/lib/ibrowse/ebin"},
debug_info,debug_info,nowarn_shadow_vars,
warn_unused_import,warn_unused_vars,warnings_as_errors,
{i,"/tmp/nix-build-ibrowse-4.2.2.drv-0/hex-source-ibrowse-4.2.2/_build/default/lib/ibrowse/include"}]
Exports:
add_config/1 send_req_direct/7
all_trace_off/0 set_dest/3
code_change/3 set_max_attempts/3
get_config_value/1 set_max_pipeline_size/3
get_config_value/2 set_max_sessions/3
get_metrics/0 show_dest_status/0
get_metrics/2 show_dest_status/1
handle_call/3 show_dest_status/2
handle_cast/2 spawn_link_worker_process/1
handle_info/2 spawn_link_worker_process/2
init/1 spawn_worker_process/1
module_info/0 spawn_worker_process/2
module_info/1 start/0
rescan_config/0 start_link/0
rescan_config/1 stop/0
send_req/3 stop_worker_process/1
send_req/4 stream_close/1
send_req/5 stream_next/1
send_req/6 terminate/2
send_req_direct/4 trace_off/0
send_req_direct/5 trace_off/2
send_req_direct/6 trace_on/0
trace_on/2
ok
2>
</programlisting>
<para>
Notice the <literal>-A erlangPackages.ibrowse.env</literal>.That
is the key to this functionality.
</para>
</section>
<section xml:id="creating-a-shell">
<title>Creating a Shell</title>
<para>
Getting access to an environment often isn't enough to do real
development. Many times we need to create a
<literal>shell.nix</literal> file and do our development inside
of the environment specified by that file. This file looks a lot
like the packageing described above. The main difference is that
<literal>src</literal> points to project root and we call the
package directly.
</para>
<programlisting>
{ pkgs ? import &quot;&lt;nixpkgs&quot;&gt; {} }:
with pkgs;
let
f = { buildHex, ibrowse, jsx, erlware_commons }:
buildHex {
name = "hex2nix";
version = "0.1.0";
src = ./.;
erlangDeps = [ ibrowse jsx erlware_commons ];
};
drv = erlangPackages.callPackage f {};
in
drv
</programlisting>
<section xml:id="building-in-a-shell">
<title>Building in a shell</title>
<para>
Unfortunatly for us users of Nix, Rebar isn't very cooperative
with us from the standpoint of building a hermetic
environment. When building the rebar3 support we had to do some
sneaky things to get it not to go out and pull packages on its
own. Also unfortunately, you have to do some of the same things
when building a project inside of a Nix shell.
<orderedlist numeration="arabic">
<listitem>
<para>Run <literal>rebar3-nix-bootstrap</literal> every time
dependencies change</para>
</listitem>
<listitem>
<para>Set Home to the current directory.</para>
</listitem>
</orderedlist>
If you do these two things then Rebar will be happy with you. I
codify these into a makefile. Forunately, rebar3-nix-bootstrap
is idempotent and fairly quick. so you can run it as often as
you like.
</para>
<programlisting>
# =============================================================================
# Rules
# =============================================================================
.PHONY= all test clean repl shell build test analyze bootstrap
all: test
clean:
rm -rf _build
rm -rf .cache
repl:
nix-shell --run "erl"
shell:
nix-shell --run "bash"
bootstrap:
nix-shell --pure --run "rebar3-nix-bootstrap"
build: bootstrap
nix-shell --pure --run "HOME=$(CURDIR) rebar3 compile"
analyze: bootstrap
nix-shell --pure --run "HOME=$(CURDIR) rebar3 do compile,dialyzer"
test: bootstrap
nix-shell --pure --run "HOME=$(CURDIR) rebar3 do compile,dialyzer,eunit"
</programlisting>
<para>
If you add the <literal>shell.nix</literal> as described and
user rebar as follows things should simply work.
</para>
</section>
</section>
</section>
<section xml:id="generating-packages-from-hex-with-hex2nix">
<title>Generating Packages from Hex with Hex2Nix</title>
<para>
Updating the Hex packages requires the use of the
<literal>hex2nix</literal> tool. Given the path to the Erlang
modules (usually
<literal>pkgs/development/erlang-modules</literal>). It will
happily dump a file called
<literal>hex-packages.nix</literal>. That file will contain all
the packages that use a recognized build system in Hex. However,
it can't know whether or not all those packages are buildable.
</para>
<para>
To make life easier for our users, it makes good sense to go
ahead and attempt to build all those packages and remove the
ones that don't build. To do that, simply run the command (in
the root of your <literal>nixpkgs</literal> repository). that follows.
</para>
<programlisting>
$ nix-build -A erlangPackages
</programlisting>
<para>
That will build every package in
<literal>erlangPackages</literal>. Then you can go through and
manually remove the ones that fail. Hopefully, someone will
improve <literal>hex2nix</literal> in the future to automate
that.
</para>
</section>
</chapter>

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<xi:include href="coding-conventions.xml" />
<xi:include href="submitting-changes.xml" />
<xi:include href="haskell-users-guide.xml" />
<xi:include href="erlang-users-guide.xml" />
<xi:include href="contributing.xml" />
</book>